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Mental Retardation: Determining Eligibility for Social Security Benefits (2002)

Chapter: 5. The Relationship of Intelligence and Adaptive Behavior

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Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

Chapter 5
The Relationship of Intelligence and Adaptive Behavior

Determining whether a person has mental retardation involves complex decisions that integrate information on current intellectual functioning and adaptive behavior. Information about each of these core dimensions is always incomplete and dependent on imperfect measures of the underlying constructs. Judgment is therefore necessary when making decisions about how best to assess intellectual and adaptive functioning and in interpreting the results; this chapter provides guidance for those judgments. However, the guidance cannot take the form of absolute decision rules that replace judgment about the appropriateness and meaning of evaluation results. For this reason, high standards and much preparation are needed for the profes-

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

sional personnel making diagnostic decisions, including thorough knowledge of mental retardation as a diagnostic construct.

This chapter discusses the diagnostic implications of the preceding chapters on intellectual functioning and adaptive behavior, as well as a review of the literature on the relationship between measures of intellectual functioning and measures of adaptive behavior. That fundamental relationship has significant implications for the discussion of how diagnostic decisions are made by combining information across multiple domains of functioning, from multiple sources, and from multiple methods of gathering information. A principle of convergent validity will emerge in this discussion as critical to a sound diagnosis of mental retardation.

DIAGNOSTIC CONSTRUCT OF MENTAL RETARDATION

Diagnostic constructs have two key components: conceptual definitions and classification criteria. Both are critical to understanding the meaning of the diagnostic construct. The four conceptual definitions of mental retardation discussed in this report (see Chapter 1) do not suggest explicit classification criteria. Although there is controversy regarding some features of these diagnostic systems (MacMillan et al., 1993, 1995; Reiss, 1994), the conceptual definitions differ little among the diverse organizations involved. It should also be noted that many other organizations and agencies establish conceptual definitions and classification criteria for mental retardation, including the Social Security Administration (SSA) and state departments of education.

Broad consensus exists throughout the developed world about the basic features of the conceptual definition of mental retardation: it involves significant limitations in the core dimensions of intellectual functioning and adaptive behavior. Most national and worldwide diagnostic systems use the term “mental retardation,” and nearly all suggest that deficits in adaptive behavior arise because of limited intellectual functioning. The greatest variations in conceptual definitions and terminology occur in the legal requirements for classification of stu-

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

dents as mentally retarded in the special education system of each state’s department of education (Denning et al., 2000; Patrick & Reschly, 1982; Utley et al., 1987). Across the 50 states and the District of Columbia, different terminology is used (e.g., mental retardation, mental disability, significantly limited intellectual capacity), along with widely varying classification criteria. Nearly all states, however, define a disability based on deficits in the dimensions of intellectual and adaptive functioning.

Controversies regarding mental retardation diagnostic systems arise most often regarding classification criteria, that is, how the conceptual definition of mental retardation is operationalized. Classification criteria vary significantly regarding the cutoff scores that are adopted to determine which cases meet or do not meet diagnostic eligibility criteria. Higher cutoff scores, of course, increase the population with a diagnosis of mental retardation, and lower cutoff scores decrease it. A little-appreciated influence is the joint effect of IQ and adaptive behavior cutoff scores on diagnostic decisions. As is shown later, the combined effects of different cutoff scores can drastically alter the number of people who can be considered for a diagnosis of mental retardation. Classification criteria also vary regarding the use of composite and part scores as well as the number of part scores that may be used from measures of adaptive and intellectual functioning.

Classification Criteria for Intellectual Functioning

The cutoff scores for measures of general intellectual functioning are better established than the cutoff scores for measures of adaptive behavior. There is broad consensus in the major diagnostic systems that performance on the intellectual dimension must be approximately two or more standard deviations below the population mean, which translates into an IQ score of 70 or less on measures with a mean of 100 and a standard deviation (SD) of 15. The degree of flexibility around the cutoff score of 70 varies among diagnostic systems; some allow a range bounded by one standard error of measurement, which

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

TABLE 5-1 Proportions of People with Scores At and Below Different Cutoff Scores on a Normally Distributed Characteristic

Cutoff Score

Percentage Meeting or Exceeding Score

Below 70

2.28

70 and below

2.68

Below 75

4.75

75 and below

5.48

Below 80

9.18

80 and below

10.20

Below 85

15.87

85 and below

17.62

translates to about 4 points for measures with reliabilities above r = .90. Other systems make a general statement that IQ can be approximately 70 to 75.

The difference between a cutoff score at or below IQ ≤ 75 and a cutoff score at or below IQ ≤ 70 is dramatic, as shown in Table 5-1. Twice the proportion of people have scores at or below 75 (5.48 percent) than have scores at or below 70 (2.68 percent). In other words, a seemingly trivial change of five points on the intellectual dimension doubles the number of people from the given population that are potentially eligible for consideration on that dimension. Before raising an alarm with this statistical information, however, it should be noted that no prevalence study of people identified as having mental retardation has ever approached the level of 5 percent of the general population, at least in part because of the necessity of a concurrent deficit in adaptive behavior. More commonly, investigations have yielded a prevalence of 1 to 1.5 percent.

The broad consensus that exists on the classification criteria for the intellectual dimension does not exist in the special education rules adopted by the states. Current state criteria on a cutoff IQ score for the intellectual dimension vary from a low of about 69 to a high of 80

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

(Denning et al., 2000). Furthermore, Patrick and Reschly (1982) found that the stringency of the IQ criterion is not always related to the prevalence of students classified as having mental retardation and placed in special education. State-to-state variations in special education rules regarding conceptual definitions and classification criteria for mental retardation lead to large differences in prevalence and many inconsistencies in the diagnosis of mental retardation between such agencies as SSA and the public schools. The use of school data is discussed later in this chapter.

Classification Criteria for Adaptive Behavior

In most diagnostic systems, the classification criteria for adaptive behavior are not developed as well or as clearly as those for intellectual functioning. Two elements are particularly relevant: the degree of difference from normal or average performance that is required to determine that a limitation in adaptive functioning exists—that is, the cutoff score—and the number of domains or areas in which limitations may be observed. Each of these elements has a significant influence on the number of people who might be considered for a diagnosis of mental retardation.

Cutoff Scores

As noted earlier, there is far less agreement on the appropriate cutoff score(s) for adaptive behavior measures than there is for measures of intellectual functioning. Precise cutoff scores generally have not been specified in diagnostic systems, primarily because of the lack of confidence in adaptive behavior measures and the availability of multiple instruments that may be used interchangeably or somewhat idiosyncratically. A selection of quotations suggests the wide range of views:

  • “If an adequate standardized instrument were available for the measurement of adaptive behavior, the upper limit of Level - I could presumably be set, as with the Measured Intelligence dimension, at greater

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

than minus one Standard Deviation from the population mean” (Heber, 1961, p. 61).

  • “If more precise instruments were available for the measurement of Adaptive Behavior, and general norms could be precisely stipulated, the upper limit could presumably be set at minus two standard deviations from the population mean” (Grossman, 1973, p. 19).

  • “It seems impractical at this time to suggest fine gradations that can be achieved with accuracy, and, in the final analysis, clinical judgment is needed to arrive at an estimate of adaptive behavior level. . . . Standardized scales, supplemented by clinical judgments whenever possible, should be applied in making diagnoses” (Grossman, 1983, p. 46).

  • “Despite increased emphasis on adaptive skills in the definition, there has been virtually no support for the use of a single global score or age equivalent index to operationalize adaptive skill limitations. There are a number of reasons why a global score and precise cutoff point would not be productive” (American Association on Mental Retardation, 1992, p. 42).

  • “The second criterion for diagnosing a person as having mental retardation is that the individual have limitations in two or more adaptive skills. This part of the diagnosis is more substantive and subjective and requires clinical judgment that takes into account environmental demands and potential support systems” (American Association on Mental Retardation, 1992, p. 49).

The American Psychological Association Division 33 (Editorial Board, 1996) mental retardation diagnostic system is the one exception to the general trend in diagnostic systems of avoiding precise specification of adaptive behavior cutoff scores to define mental retardation eligibility. The Division 33 scheme is explicit in recommending the use of a “comprehensive, individual measure of adaptive behavior” (p. 13) and in specifying precise cutoff scores:

For adaptive behavior measures, the criterion of significance is a summary index score that is two or more standard deviations below the mean for the appropriate norming sample or that is within the range of adaptive behavior associated with the IQ range sample in instrument norms (Editorial Board, 1996, p. 13).

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

In its next paragraph, the Division 33 discussion allows for part scores, but the criterion for eligibility is that “two or more of these scores lie two or more standard deviations below the mean” (p. 13). The Division 33 system also adopted the now rather standard criterion of intellectual functioning at two or more standard deviations below the mean. The consequences of these requirements on the number of people currently considered for a diagnosis of mental retardation or on the number of persons considered in the future have not been addressed. The results of previous studies had suggested that a stringent criterion for adaptive behavior plus the usual criterion for intellectual functioning led to a sharply reduced number of people eligible to be considered for a mental retardation diagnosis (Heflinger et al., 1987; Reschly, 1981a). However, these studies used a particular measure of adaptive behavior that had a very low correlation with measures of intellectual functioning.

The classification criteria governing diagnosis of mental retardation for special education services by state departments of education generally do not provide guidance regarding the use of adaptive behavior composites, part scores, or cutoff scores to determine eligibility. It is not surprising that the use of an adaptive functioning criterion in the schools is inconsistent and unpredictable (Reschly & Ward, 1991). Moreover, enormous variations exist across the states and, in some instances, across local school districts within states.

Adaptive Behavior Domains

Diagnostic systems are either silent on the appropriate number of adaptive behavior domains, or they adopt widely varying schemes. The most recent classification system of the American Association on Mental Retardation (AAMR) specifies 10 adaptive skills areas without any explanation of how that number was determined or why some domains were included and others excluded (American Association on Mental Retardation, 1992). In contrast, the American Psychological Association Division 33 diagnostic system is generally consistent with the factor analytic literature (see Chapter 4 and later discussion in this

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

chapter) in specifying the use of a composite score, recognizing that a general adaptive behavior factor exists, and the use of a limited number of part scores.

The appropriate number of domains in the assessment of adaptive behavior depends on the instrument, age level, and other considerations. Some useful guidance on the number of meaningful domains is provided by factor analytic studies; however, different factor methods yield different results, so such studies are rarely definitive. Most adaptive behavior scales yield a general factor, regardless of the number of domain or subdomain scores, if the analytic method permits the emergence of such a factor (e.g., Harrison & Oakland, 2000a; McGrew & Bruininks, 1989). Typically, one or more group factors also emerge, particularly if (a) confirmatory factor analytic procedures are applied, (b) items reflect diverse areas of functioning, (c) sufficient floors and ceilings are provided, (d) broad age ranges are included, and (e) individuals from the moderate and mild levels of mental retardation, as well as people with borderline and normal levels of functioning, are included in the sample. Across all ages, McGrew and Bruininks suggested the possibility of four or five group factors. This literature is discussed in detail in Chapter 4.

Beyond its theoretical importance, the appropriate number of adaptive behavior domains has a very practical significance: it can have a tremendous influence on the number of people who may be diagnosed as having mental retardation and therefore are eligible for Supplemental Security Income (SSI) and Disability Income (DI) benefits. At the request of the committee, Thompson (2001) ran a series of Monte Carlo simulations to address this effect. She found that the number of adaptive behavior domains on which deficits must be shown had a marked effect on identification rates, with more individuals being identified as having mental retardation if only a single adaptive behavior domain had to meet a defined cutoff score than if two or more domains had to meet a cutoff score. Furthermore, the number of domains on which deficits could be measured had a modest but significant effect on identification rates: more individuals will be diag-

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

nosed as having mental retardation if deficits can be found in 1 or 2 out of 9 or 10 domains, than if deficits are found in 1 or 2 of only 4 domains of adaptive behavior. In other words, it is easier to qualify for a diagnosis of mental retardation if there are more domains in which deficits can be shown.

It is important to remember that expectations about adaptive behavior and competence vary by sociocultural group, settings, and age levels. The conceptual definition and descriptions of adaptive behavior in the 1983 AAMR manual (Grossman, 1983) have been particularly instructive in this regard because in it different competencies were associated with broad age ranges (e.g., preschool, childhood, adolescence, adult). The committee considered the interaction of age-based expectations and adaptive behavior domains, including the current domains identified in the SSA listings (see Table 5-2). Clearly, the current SSA scheme recognizes different domains at different age levels and is similar in most respects to the adaptive domains discussed in Chapter 4. In other respects, however, the SSA domains are inconsistent with findings from factor analytic results, the descriptions of adaptive behavior in authoritative sources, and the content of current adaptive behavior inventories. This led to the committee’s recommendation, presented in Chapter 4, for revising the SSA adaptive behavior domains (see right side of Table 5-2).

The SSA domain of concentration, persistence, and pace is not assessed by most adaptive behavior instruments, although these skills could be part of the work attitudes and skills domain recommended for adults. The current SSA domains do not include some that are prominent in current conceptions and measures of adaptive behaviors, particularly the self-help and communication domains in the preschool years. For childhood and adolescence, the SSA scheme does not include motor/mobility, communication/functional academics, or daily living skills, although the latter may be covered by SSA in the domain of personal functioning. And, the communication/functional academics and work attitudes and skills domains are missing from the SSA adult domains. The adaptive behavior areas specified in Table 5-2 are

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

TABLE 5-2 Adaptive Behavior Domains in Current Social Security Administration Regulations and Committee Recommendations

Age

Social Security Administration Domains

Age

Committee Recommendations

Birth-2

1. Motor (fine/gross)

2. Social

Birth-4

1. Motor

2. Social

3. Self-help

4. Communication

3-17

1. Personal

2. Social

3. Concentration/persistence/pace

5-17

1. Motor/mobility

2. Social

3. Communication/functional academics

4 Daily living skills

18+

1. Daily living

2. Social

3. Concentration/persistence/pace

18+

1. Motor/mobility

2. Social

3. Communication/practical cognitive skills

4. Daily living skills

5. Work

the ones recommended by the committee to be adopted by SSA to guide decisions about diagnoses of mental retardation (the recommendation itself appears in Chapter 4).

Most current adaptive behavior measures have domains that are similar to the domains recommended by the committee; however, no scale is perfectly matched to these domains. Moreover, essential content, such as functional academic skills involving basic literacy, temporal relationships, and quantitative concepts, appears on most scales, but in different domains. For example, the area of functional academic skills is a separate domain in the Adaptive Behavior Assessment Scales (ABAS—Harrison & Oakland, 2000a) and the Comprehensive Test of Adaptive Behavior (CTAB—Adams, 2000), but it is spread over

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

at least two domains in the Vineland Adaptive Behavior Scales (VABS—Sparrow et al., 1984a) and the Scales of Independent Behavior-Revised (SIB-R—Bruininks et al., 1996). Valuable information from each of these instruments on the functional academic skills area is available, but direct translation of the available scores to a decision about performance in this area is difficult. Similar relationships exist between the available scores from instruments and the recommended areas in Table 5-2. Decisions about performance in each of these areas therefore need to be based on the results of adaptive behavior instruments, to the extent that one or more instruments are appropriate for a given client, and a broad variety of other information.

RELATIONSHIP OF ADAPTIVE BEHAVIOR AND INTELLECTUAL FUNCTIONING

The relationship between measures of adaptive behavior and intellectual functioning is highly variable and has multiple influences. Correlations between adaptive and intellectual functioning have varied in published studies from near zero (no relationship) to nearly 1.0 (perfect relationship). The strength of this relationship is important because it influences diagnostic decisions significantly.

Variables That Influence Correlations

A comprehensive review by Meyers et al. (1979) summarized data on the correlations of measures of adaptive and intellectual functioning. This section is informed by that review as well as by data published in test manuals over the past 20 years. Newer adaptive behavior scales generally conform to the generalizations made by Meyers et al. in 1979.

Scale Content

A major influence on the relationship of adaptive and intellectual functioning is the content of the measures, particularly the adaptive

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

behavior measure. Very low correlations are obtained with adaptive behavior scales that do not include content on practical, everyday cognitive skills. For example, scores on the Adaptive Behavior Inventory for Children (ABIC) (Mercer & Lewis, 1978) have an extremely low correlation with scores on the Wechsler Intelligence Scale for Children-Revised (WISC-R), according to the manual and other studies (Kazimour & Reschly, 1981). The effect of using the ABIC in mental retardation classification decisions was to eliminate the mild level (IQ 55 to 70 or 75) because virtually no one with an IQ in that range had an adaptive behavior score that was more than –1 or –2 SD below the mean (Heflinger et al., 1987; Reschly, 1981a).

The composite and domain scores on adaptive behavior measures that include practical, everyday cognitive skills show higher relationships with intellectual functioning; for example, the correlations with intellectual measures for the communication domain on the VABS is about 0.4 (Sparrow et al., 1984a), and the functional academic skills area of the ABAS (Harrison & Oakland, 2000a) is about 0.5. In contrast, the VABS domains of daily living skills, socialization, and motor skills have correlations with IQ that vary from about .20 to about .35. The relatively low correlations that many adaptive behavior measures have with IQ tests mean that many individuals low on one of the measures may not be low on the other, an outcome that has important implications for mental retardation diagnoses. Correlations may also be low because of ceilings on adaptive behavior measures or because of the attenuation of the correlation between adaptive behavior and intelligence among people with IQs above 100.

Competencies Versus Perceptions

Adaptive behavior measures typically reflect the judgment of a respondent about a client’s performance, which also influences correlations of adaptive behavior measures with IQ scores. Generally, adaptive behavior items that do not reference specific behaviors are less likely to correlate highly with IQ test results. For example, an item that asks, “Does Egbert read common signs?” with response choices

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

such as “Often, Sometimes, Never” is less likely to yield precise information on skills than items that reference specific behaviors, like “Can Esmerelda read a rest room sign and act accordingly?” The latter focuses on a “can do” skill rather than a respondent’s perception of the client’s participation in some activity. Scores on scales with more behaviorally specific skills generally have higher correlations with measures of intellectual functioning (Adams, 2000; Harrison & Oakland, 2000a).

Sample Variance

All correlational studies depend on sample variability, and the relationship of adaptive and intellectual functioning measures is no exception. Research studies that include participants who score very differently on both measures will generally produce higher correlations, other things being equal. Constraints on sample variability in a study ensures lower correlations.

Ceiling and Floor Problems

Most adaptive behavior measures have an insufficient number of items at the highest levels of performance for clients or study participants; this is called a ceiling problem. Insufficient numbers of items at the lower levels of performance create floor problems. Both intellectual and adaptive behavior measures often have ceiling and floor problems, most often at the extremes of ability or near the bottom and top ages covered by the instrument (see Chapters 3 and 4 for a more complete discussion of these issues). Generally, for individuals with low intellectual functioning, problems with intellectual measures are likely to be insufficient floors. For adolescents and adults with IQs from 60 to 85, or who have intellectual skills in the normal range, the opposite problem occurs with adaptive behavior measures, which usually do not have sufficiently high ceilings. Absence of a sufficient number of ceiling items produces very low IQ by adaptive behavior correlations for adults on most measures, although the ABAS (Harrison & Oak-

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

land, 2000a) suffers less from this problem than do other adaptive behavior scales.

Level of Mental Retardation

In their review of research, Meyers et al. (1979) found that for young children functioning far below average, the results of intellectual functioning and adaptive behavior measures were nearly identical. In fact, for extremely low levels of functioning on both types of test, nearly the same items are used on measures of adaptive and intellectual functioning, providing a ready explanation for the nearly perfect relationship. It is reasonably safe to say that at the severe and profound levels of mental retardation (Grossman, 1983), particularly with young children, little difference exists between the constructs of adaptive and intellectual functioning.

The relationship of adaptive and intellectual functioning measures is less certain with individuals functioning in the moderate and mild levels of mental retardation as defined by IQ. In the VABS manual (Sparrow et al., 1984a), correlations between various intellectual measures and VABS domain and composite scores are reported for adults with mental retardation who were in residential and nonresidential living arrangements. The correlations for the VABS composite score and the Wechsler or Stanford-Binet intellectual measures were generally slightly higher (r = .4 to .5) than similar correlations for normal children (r = .32). The samples of adults had mean IQs that varied from about 25 to 50, suggesting that these VABS correlations were derived from samples of people with moderate to severe mental retardation. Few persons in these samples were in the range of mild mental retardation, the ability range that is most relevant to the committee’s deliberations.

Harrison and Oakland (2000a) reported the relationship of the ABAS composite to Stanford-Binet Fourth Edition IQs for a “clinical” sample composed of children with autism (15 percent of the sample) and mental retardation (85 percent of the sample). The mean IQ for this sample was about 51, suggesting that most of the participants had

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

intellectual ability scores indicating the moderate level of mental retardation. This ABAS correlation with IQ is virtually the same for people without mental retardation and for those with autism or mental retardation, but, again, this correlation does not bear directly on the relationship of adaptive behavior and intellectual functioning for people in the critical IQ range of 60 to 75.

The preponderance of the evidence suggests that the correlations between measures of IQ and adaptive behavior are higher for individuals with severe or profound levels of mental retardation. The lower the IQ level within the range from about 20 to 40, the higher the correlation to adaptive behavior scores. The magnitude of this relationship for people with the moderate level of mental retardation is less certain, but it appears to be slightly higher than for people without this disability. Sufficient evidence is not available regarding the intellectual functioning and adaptive behavior relationship for people in the mild range of mental retardation, although extrapolating the findings just cited for the profound, severe, and moderate levels leads to the conclusion that the relationship is either no higher or only very slightly higher than for people without cognitive disabilities. It also leads us to conclude that the best and most accurate guide to the IQ and adaptive behavior relationship in the IQ 60 to 75 range is the correlation for people without cognitive disabilities, unless there are other specific results for people with mild mental retardation. None of the recently published adaptive measures has supplied information for this particular population.

It should be noted that high correlations of IQ and adaptive behavior have been reported for one adaptive behavior measure and that they may be spurious. Bruininks et al. (1996) reported that for children ages 5 to 12, the correlation between scores for adaptive behavior on the SIB-R and IQ was .78, but only .20 for adolescents and adults ages 13 to 90. The overall correlation between these two measures across all ages, 3 to 90, was .82. These unusually high correlations are probably due to contamination of the correlations with changes in developmental level. For that reason, the SIB-R correlations reported in

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

the manual may not be accurate estimates of the relationship of the SIB-R scores and intellectual functioning.

Classification Agreement: IQ and Adaptive Behavior

A critical issue related directly to the committee’s recommendation on combining IQ and adaptive behavior data is the classification agreement between measures of intellectual functioning and adaptive behavior. Classification agreement studies form part of the basis for determining appropriate cutoff scores on adaptive and intellectual functioning measures. The ideal data set would be large samples of people functioning in the range of borderline to the high end of moderate mental retardation. Diagnosis of mental retardation could be studied using different cutoff scores (–1 SD, –1.66 SD and –2 SD) on both measures simultaneously. The results would be informative about the implications of establishing different assessment requirements and the application of different eligibility criteria. However, actual data of this kind generally are not available; the committee therefore commissioned two sets of Monte Carlo simulations to assist in our analysis.

Classification Agreement: Existing Data

Few data exist on the classification agreement between recently published adaptive behavior measures and intelligence tests. As discussed at length in Chapter 4, only one test manual contains data that are relevant to this issue (Harrison & Oakland, 2000a, p. 89, Table 5.31). The data in Table 4-3 show that nearly 25 percent of the people with a preexisting diagnosis of mild mental retardation did not score 2 or more SDs below the mean on two adaptive behavior domains, demonstrating that this is not an appropriate criterion for a diagnosis of mental retardation.

These results should not be generalized to other adaptive measures. It should be pointed out that it is easier to meet a limitations criterion if, as in this case, more adaptive behavior subareas are used.

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

That is, 1 or 2 deficits out or 9 or 10 subareas is an easier criterion to meet than 1 or 2 deficits out of 4 or 5 subareas.

Although the committee searched, no further studies of the classification agreement between recently published adaptive behavior measures and IQ were found. The authors of other adaptive behavior measures have not provided data of this nature, even though the current and previous editions of the Joint Association Test Standards (Joint Committee on Standards for Educational and Psychological Testing of the American Educational Research Association, the American Psychological Association, and the National Council on Measurement in Education, 1985, 1999) require that test publishers provide validity data supporting the recommended uses of a test.

Simulations of IQ and Adaptive Behavior Classification Agreement

Because of the dearth of data examining the relationship between various levels of IQ and scores on adaptive behavior measures, particularly for individuals in the mild mental retardation range, the committee used Monte Carlo models to project the proportion of people who would be expected to have IQ and adaptive behavior domain scores in specific ranges. These Monte Carlo models used correlations of adaptive behavior domain scores with one another and with IQ (Thompson, 2001). The simulations used the best of the currently available adaptive behavior measures, applying assumptions that enhanced the likelihood of classification agreement between IQ and adaptive behavior. For example, high-end estimates of the relationship between adaptive and intellectual functioning were applied as well as internal consistency reliability estimates, rather than stability coefficients, making classification agreement slightly more likely. Projections of the proportions of adult cases meeting IQ and adaptive behavior cutoff scores were developed from the Monte Carlo analyses and are summarized in Tables 5-3 and 5-4. These projections were based on test manual data on the correlations of domain scores with one another and with IQ. The Monte Carlo results answer the question: Given an IQ in the range of mental retardation, how many cases will

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

TABLE 5-3 Monte Carlo Simulations of the Proportions of Children and Adults Eligible to be Considered for a Mental Retardation Diagnosis Using the VABS and SIB-R at Varying IQ and Adaptive Behavior Cutoff Scores

Adaptive Behaviora

IQ Cutoff Score

 

No. of Deficits

Cutoff

IQb

<60

IQc

60-70

IQd

60-75

1

≤ 70

28-46

20-30

18-26

1

≤ 77.5

51-71

41-55

37-49

1

≤ 85

72-88

64-78

60-74

2

≤ 70

9-22

6-12

5-9

2

≤ 77.5

23-45

17-30

15-25

2

≤ 85

46-71

38-55

35-50

NOTE: VABS = Vineland Adaptive Behavior Scales. SIB-R = Scales of Independent Behavior-Revised.

a Adaptive behavior status refers to any one or any two of four part scores from the VABS or SIB-R.

b All persons with IQs below 60 are presumed eligible to be considered for a diagnosis of mental retardation according to current Social Security Administration criteria. The proportions in this column show the proportions of individuals with IQs below 60 who also have adaptive behavior scores below different cutoff scores.

c This column provides data on individuals with IQs of 60 through 70. Persons with IQs below 60 or above 70 are not included.

d This column presents data on individuals with IQs from 60 through 75. The proportions reflecting classification agreement are lower in column five than four because a smaller proportion of cases in the 71-75 IQ interval have low adaptive behavior scores compared with cases in the 60-70 interval.

have adaptive behavior scores that meet the different cutoff scores? For example, looking at the results in the first row, third column, it appears that for people with IQs of less than 60, between 28 and 46 percent meet the standard of at least one adaptive behavior part score at or below the cutoff of 70.

In Table 5-3, findings are presented jointly for two adaptive behavior scales that are well standardized and supply a composite score and four part scores, the VABS (Sparrow et al., 1984a) and the SIB-R

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

TABLE 5-4 Monte Carlo Simulations of the Proportions of Children and Adults Eligible to Be Considered for a Mental Retardation Diagnosis Using the ABAS at Varying IQ and Adaptive Behavior Cutoff Scores

Adaptive Behaviora

IQ Cutoff Score

No. of Deficits

Cutoff

IQb

<60

IQc

60-70

IQd

60-75

1

≤ 70

46-57

34-40

30-35

1

≤ 77.5

70-80

59-66

53-60

1

≤ 85

87-93

79-86

75-82

2

≤ 70

31-37

21-23

18-20

2

≤ 77.5

56-64

43-48

38-43

2

≤ 85

78-85

67-74

63-69

Note: ABAS = Adaptive Behavior Assessment Scales.

a Adaptive behavior status refers to any 1 or any 2 of the 9 ABAS adaptive skills areas for children or 10 adaptive skills areas for adults.

b All persons with IQs below 60 are presumed eligible to be considered for a diagnosis of mental retardation according to current Social Security Administration criteria. The proportions in this column show the proportions of individuals with IQs below 60 who also have adaptive behavior scores below different cutoff scores.

c This column provides data on individuals with IQs of 60 through 70. Persons with IQs below 60 or above 70 are not included.

d This column presents data on individuals with IQs from 60 through 75. The proportions reflecting classification agreement are lower in column five than column four because a smaller proportion of cases in the 71-75 IQ interval have low adaptive behavior scores compared with cases in the 60-70 interval.

(Bruininks et al., 1996). The part scores conform generally to the adaptive behavior domains recommended in Table 5-2 and to the factor analytic results discussed in Chapter 4. The four VABS part scores included in the Monte Carlo analyses were motor, independent living, communication, and social. The SIB-R part scores were motor skills, personal living skills, community living skills, and social interaction/ communication skills. Examination of the proportions of cases in the simulations with various combinations of low IQ and low adaptive behavior scores provides an estimate of the effects of altering the cutoff scores for both measures.
Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

Six adaptive cutoff scores were used in one domain at –2.0 SD (≤ 70), –1.5 SD (≤ 77.5), and –1.0 SD (≤ 85), and in two domains at the same cutoffs of -2.0 SD, -1.5 SD, and –1.0 SD (Table 5-3, columns 1 and 2). Classification agreement with three IQ criteria was simulated, IQ < 60, IQ ≥ 60 but ≤ 70, and IQ ≥ 60 but ≤ 75 (Table 5-3, columns 3-5). Proportions of cases in the simulations that met various combinations of IQ and adaptive behavior cutoff scores are shown in the table.

The results in column 3 of Table 5-3 indicate that many people with IQs of less than 60 do not meet the cutoff score requirements for a deficit in adaptive behavior. As noted earlier, SSA defines all persons with an IQ of less than 60 as presumptively eligible to be considered for a diagnosis of mental retardation, and the committee recommends continuing that practice. The imperfect classification agreement between IQ and adaptive behavior at low IQ levels indicates that caution must be used in proposing the adoption of adaptive behavior cutoff scores. Consider individuals with IQs of less than 60 and the most lenient adaptive behavior cutoff score, deficits in one domain at or below 85 (see row three): only 72 to 88 percent of cases met the dual IQ and adaptive behavior criteria. Adoption of any adaptive behavior cutoff score even with persons presumptively eligible due to IQs below 60 could result in 12 to 18 percent of those currently eligible to be considered for a diagnosis of mental retardation becoming ineligible.

Examination of other combinations of IQ and adaptive behavior scores further supports the use of caution in setting an adaptive behavior cutoff score. In column 4 of Table 5-3, an IQ between 60 and 70 and a stringent criterion of two adaptive behavior domains at or below 70 yields a hit rate of only 6 to 12 percent, a level that is far below the stipulation that most people with IQs at or below 70 should be eligible to be considered for a diagnosis of mental retardation. Even the most lenient criterion included in the simulation, a deficit in one adaptive behavior area at a cutoff at or below 85, resulted in only 64 to 78 percent of cases meeting the dual criteria of an IQ score between 60 and 70 and an adaptive behavior score at or below 85. Other combinations also are instructive. At the criterion of two adaptive behavior

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

domains at or below 85, only 38 to 55 percent of persons with IQs between 60 and 70 met the dual classification criteria (see last row in column 4).

The two adaptive behavior inventories differed regarding the rate of classification agreement with IQ in the Monte Carlo simulations in Table 5-3. Higher classification agreement occurred with the SIB-R children simulation and the lowest with the VABS children simulation. Using these scales, the classification agreement for adults probably should not be done because both scales have ceiling problems for individuals with mild mental retardation or borderline functioning who are in the late adolescent or adult years. Finally, it bears repeating that these simulations adopted assumptions that probably enhanced the degree of classification agreement and therefore are likely to overestimate the degree of classification agreement in actual practice.

Thompson (2001) conducted additional Monte Carlo simulations with the ABAS (Harrison & Oakland, 2000a). The combined results for children and adults are presented in Table 5-4. The number of ABAS adaptive skills areas is 9 for children and 10 for adults. It is easier to achieve classification agreement when more adaptive skills areas are included. Generally, it should be expected that the proportions indicating classification agreement will be higher in Table 5-4 than Table 5-3 due to the greater number of adaptive skills areas (9 or 10 areas in Table 5-4 versus 4 areas in Table 5-3) and the higher correlations for the ABAS than the VABS or the SIB-R. Nevertheless, a significant number of cases in the Monte Carlo simulation with IQs in the range of mental retardation do not have significant adaptive behavior deficits using the ABAS.

The uncertainty regarding the effects of different adaptive behavior cutoff scores is further increased by comparing the results in Tables 4-3 and 5-4. Both tables use data from the ABAS. In Table 4-3, real data are reported for a “convenience sample” of children and youth with mild mental retardation whose characteristics were not fully described. For that group, the authors reported that 76 percent had two or more adaptive skills area scores at or below 70. The ABAS Monte Carlo analyses using the cutoff of adaptive behavior at or below 70

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

revealed far lower proportions meeting the criterion of two or more adaptive behavior areas in the range of mental retardation. Having no way to reconcile these inconsistent results regarding the ABAS, the committee had to take the uncertainty caused by these results into consideration when recommending an adaptive behavior cutoff score.

Conclusions

Caution in the adoption of precise adaptive behavior cutoff scores is warranted by the limited evidence on the classification agreement between IQ and adaptive behavior measures at varying cutoff scores. Monte Carlo simulations, conducted to estimate the probable effects of varying adaptive cutoff scores, yielded results indicating the classification agreement often was rather low using the best of the currently available adaptive behavior measures. The inconsistencies between ABAS actual data, albeit from a limited sample, and the ABAS simulations provide further support for caution in recommending precise cutoff scores.

It is not possible to simulate score distributions for people who would actually be referred for benefits; such a distribution may be somewhat different and possibly reflect more pronounced functional limitations. It may also be the case that a simulation, as in the current instance, must be based on parameters for all people in a norming sample for whom information is available, rather than on people with a more restricted IQ range. Such considerations will affect the degree to which the simulation reflects actual circumstances and the functional characteristics of cases reviewed for benefits eligibility.

The committee’s formal recommendation about the use of adaptive behavior scales, presented in Chapter 4, is predicated on the dual goals of providing reasonable guidance for decision making and avoiding the massive declassification effects of an excessively stringent cutoff. The cutoff scores recommended represent the committee’s long deliberations about the relative effects or more or less stringent criteria. In the committee’s judgment, the same cutoff score could not and should not be used for IQ and adaptive behavior due to the near cer-

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

tainty of massive declassification effects. We explicitly rejected the use of a –2 SD adaptive behavior cutoff score. The committee was, however, reluctant to allow an arbitrary adaptive behavior cutoff score to be used or to adopt the most lenient of the various scores that were investigated.

In order to fulfill our charge of providing more guidance to SSA regarding adaptive behavior and our obligation to use the best available science in making recommendations, the committee decided to recommend some discretion regarding the interpretation of the results of formal measures of adaptive behavior. That is, a formal assessment of adaptive behavior should be provided in all cases. However, a person may be diagnosed as having mental retardation even if the adaptive behavior results do not meet the cutoff criteria if there is compelling evidence of adaptive behavior deficits that significantly impair performance of expected behaviors. It is the obligation of those gathering and interpreting adaptive behavior information to make a compelling case if it is warranted.

SSI AND DI ELIGIBILITY DECISIONS

Only professionals who have extensive knowledge about mental retardation and its assessment and who are using extensive information about an individual from multiple sources and settings should formulate eligibility decisions, because they have such profound consequences for the lives of clients and their families. Since there are four possible outcomes in any diagnostic setting and two of them are errors (Coombs et al., 1970; Swets et al., 2000), diagnoses must be made extremely carefully. A true positive or “hit” occurs when mental retardation is present and the diagnosis is correct. Similarly, a true negative or “correct rejection” occurs when mental retardation is not present and the diagnosis indicates that. Anything else is an error: a diagnosis of mental retardation when it is actually absent is a false positive or “false alarm.” Finally, a diagnosis of no mental retardation when it is actually present is a false negative or “miss.”

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

If the diagnostic decision is incorrect, whether it confirms or denies eligibility, it is likely to be related to negative consequences for individuals, their families, and society. Incorrectly confirming eligibility results is a waste of scarce public resources and may diminish the client’s motivation and opportunities to engage in normal activities of work and economic self-support. Incorrectly denying eligibility has equally harsh consequences for individuals and families involving, in extreme cases, lack of access to the basic necessities of life. Decisions with consequences of this magnitude must be made by knowledgeable persons using the best information available and applying a principle of convergent validity. They must also understand the types of errors that are likely to occur in situations as complex and challenging as determination of mental retardation.

Common Judgment Errors

A confirmation bias can occur when a decision maker seeks information that confirms an already existing hypothesis or judgment (Evans, 1989). The best course of action when examining a hypothesis is to seek evidence that tests the idea by seeking disconfirming evidence. However, “it is a common observation in psychological research that individuals tend to selectively search for evidence to support their views at the expense of seeking contrary evidence” (Bunn, 1992, p. 253).

This tendency to look for confirming, rather than disconfirming, evidence has clear implications for eligibility decisions. If examiners focus primarily on seeking supporting evidence, then errors are almost inevitable. Furthermore, examiners are unlikely to know that they have made errors or why, since the evidence they have gathered will tend to support their decisions. Thus, the confirmation bias can lead to a pattern of self-perpetuating errors. Active countermeasures are needed to reduce the impact of judgment biases, like seeking disconfirming evidence in a systematic fashion or using a structured examination process instead of an unstructured one.

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

In many judgment situations, initial impressions have been found to heavily influence the final decision. In a classic paper, Asch (1946) described the primacy effect, in which later evidence is interpreted in the light of earlier evidence; the early evidence actually causes a change of meaning in the later evidence. Stewart (1965) was one of the first to propose attention decrement as an explanation for primacy. He reasoned that changing a task so that subjects were forced to attend to later evidence should diminish the primacy effect. He found this to be true, but only when subjects responded at the end of the task sequence. If responses are made to each new piece of evidence as it becomes available, the effect is reversed; evidence appearing later in the sequence actually had a greater impact—a recency effect. Many studies have shown that primacy effects can be reversed to recency effects using a variety of attentional manipulations. When left to our own resources, however, we tend to emphasize whatever we know first about a person—a primacy effect. In the context of eligibility determination, the same information can lead to different impressions depending on the selection and order of the assessments. Thus, the order of the impression formation can be significant in determining the outcome of the process.

Comprehensive Evaluation

Eligibility decisions must be based on a comprehensive evaluation of the person and the environment in which he or she lives and works. Opportunities as well as demands in that environment must be considered along with the client’s status on broad domains of human functioning. Physical, emotional, adaptive, and cognitive functioning must be considered, and current SSA guidelines are consistent with this principle.

The tendency of clinicians engaged in evaluations of mental retardation to focus almost exclusively on intellectual and adaptive functioning, ignoring other important information on overall mental health and emotional adjustment, has been called “diagnostic overshadowing” (Reiss et al., 1982; Reiss & Szyszko, 1983). Information about low

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

intelligence and poor adaptive functioning has been known to overshadow other clinical information that suggests the presence of other mental or emotional disorders that meet formal diagnostic criteria. A number of studies conducted since 1980 confirms that type of bias on the part of the clinician and the frequent existence of psychopathology accompanying mental retardation (e.g., White et al., 1995). Many persons with mental retardation are eligible for dual diagnoses, a simultaneous diagnosis of mental retardation and some other physical or mental disorder, such as depression, conduct disorder, or sensory impairment. It is crucial that clinicians evaluating individuals for the diagnosis of mental retardation also look for other emotional, mental, and physical disorders that may complicate adaptive and intellectual functioning and confer eligibility in other SSA categories (see Chapter 6).

Consideration of Other Information on Intellectual and Adaptive Functioning

There is clear consensus in the human services professions that a broad variety of information must be collected and evaluated regarding the individual in addition to and, in many cases, independent of the results of standardized tests and inventories. No single test or inventory score should be the sole basis for a significant decision. Moreover, for some clients, formal instruments are inappropriate due to a poor match between the client’s characteristics and the nature of the test or inventory requirements. None of the authors of major testing instruments claims that other information is irrelevant or that information from other sources confirming or disconfirming the results of a standardized instrument should be ignored. It is useful to consider different methods of data collection, different sources of information, and performance in different settings.

Methods for Collecting Data

Four methods of collecting assessment information have been described in the literature: direct testing of clients, observation of behav-

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

ior in one or more settings, review of records reflecting previous and current performance, and interviews with the client and knowledgeable others. Disability determination examiners should be familiar with and utilize each of the methods in developing a well-informed perspective on the functioning levels of clients considered for a mental retardation diagnosis.

Direct testing of clients’ adaptive behavior is a rarely used technique, even though direct testing of general intellectual functioning is the norm. Yet, at least some direct testing is appropriate with adaptive functioning. For example, functional academic skills, such as basic literacy, understanding temporal relationships, and quantitative concepts, are crucial to adaptive functioning for children, adolescents, and adults. Adults who cannot tell time or meet time-related work obligations are at a significant disadvantage in coping with everyday demands. Information from third-party respondents on these skills may or may not be accurate, especially as these skills relate to everyday functioning. Some adaptive behavior measures suggest establishing conditions under which behaviors can be “tested” if third-party respondents are unable to report their actual observations of the behavior (Adams, 2000).

Interviews with third-party respondents by using standardized adaptive inventories is the most common method for collecting adaptive behavior information. For children, the third party is most often a parent or a teacher. While third-party interview is not used extensively in intellectual assessment, the results of IQ tests should be further evaluated through interviews with the client and significant others to determine if the observed test performance is consistent with day-to-day functioning. In addition to third-party respondents, interviews with clients and other parties are components of a comprehensive adaptive behavior assessment. One adaptive behavior instrument has been normed with adults using a self-report format; however, no data were provided in the manual contrasting the self-report and third-party respondent results for persons with mild mental retardation (Harrison & Oakland, 2000a). The accuracy of individuals with mild mental retardation in reporting their own adaptive behavior on this instru-

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

ment is not yet clear; nevertheless, unstructured and structured interviews with clients are necessary for determining if adaptive behavior deficits exist.

Observations of clients’ intellectual functioning and adaptive behaviors can be systematic and structured or informal and anecdotal. Both techniques yield valuable information for understanding overall functioning. Opportunities for systematic observation of clients’ adaptive behaviors are limited by resource constraints and the near impossibility of conducting highly structured observations in all relevant settings and at the times that are appropriate. Moreover, many adaptive behaviors that are crucial to adequate functioning do not occur frequently, making systematic observation even more difficult. Therefore, even informal and anecdotal observations from different people and across different settings are valuable to an overall decision about adaptive behavior and should be obtained to the extent feasible.

Review of records is another data collection method with strong applicability to the determination of intellectual and adaptive behavior deficits. School records are especially useful if evaluators understand the nature of mental retardation, classification practices in schools, and subtle indicators of low functioning in classrooms and schools. However, school records indicating either a diagnosis of mental retardation or the absence of one cannot be used as a definitive indication of intellectual and adaptive behavior status. Records from agencies other than schools can also be useful in determining adaptive behavior deficits. Medical, social service, and legal sources may yield further information that is useful in making judgments about deficits. Further discussion of the use of records from schools and other agencies in order to make diagnostic decisions appears below.

Sources of Information

Judgments about intellectual and adaptive functioning should be based on multiple sources of information including, at a minimum, the individual client and significant others such as (depending on age) parents, teachers, peers, neighbors, and family members. The kind and

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

amount of information gathered from different people will vary significantly across clients. In some cases, judgments must be based primarily on an interview with a single third-party respondent and on observations or interviews with the client, while in other cases there will be multiple sources of information. SSA disability examiners have to make judgments about the sufficiency of the information in deciding whether to actively seek additional sources of information.

Settings

The client’s functioning across different settings is also relevant to decisions about intellectual and adaptive behavior deficits. The settings that are most relevant depend on the client’s developmental level. For preschoolers, the relevant setting is the home and, depending on the client, day care or preschool settings. For children between ages of about 5 and 18, the school and home settings are crucial for nearly all clients, as are skills in meeting expectations as they age for roles in the neighborhood and the community. Deficits that are apparent only in a single setting generally should not be the basis for a determination of an adaptive behavior deficit. Diligence in collecting and examining information from multiple settings is very important.

The literature refers to so-called six-hour retarded children (President’s Committee on Mental Retardation, 1970), described as having performance deficits only in school settings and coping adequately in home and community settings. “Six-hour retarded children” were assumed by many to blend into the normal adult population without significant adaptive limitations. Studies of young adults who clearly met this conception yielded a very different picture (Koegel & Edgerton, 1984). Contrary to the assumptions, as young adults, these children had enormous difficulties in coping with everyday demands and avoiding being exploited by others due to their functional limitations in practical cognitive and other adaptive skills.

Current classification and placement practices make it less likely that children will be identified in this way in schools (see later discussion), but many of them do have significant problems coping with the

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

everyday demands involving social relations with peers and negotiating the cognitive demands required for personal and social adaptation outside school. Careful analysis of how children and adolescents perform in school, home, and other settings must be made in order to come to the most accurate diagnosis.

Examiner Qualifications

Individuals making mental retardation diagnoses must meet high standards regarding professional preparation and relevant experience. SSA disability examiners should have in-depth and up-to-date knowledge in the following areas: mental retardation theory, research, treatment, and best practices; mental retardation diagnostic construct; measurement of intellectual and adaptive functioning; assessment principles and best practices; mental disorders theory, research, and best practices; purposes and practices of multiple agencies, such as schools, law enforcement, and health care; knowledge of human development; and assessment of the individual’s strengths and limitations in the context of multiple environments, including family, work, and community.

Convergent Validity

Convergent validity is an application of the concept of the multitrait/multimethod examination of the validity of measures of psychological constructs (Campbell & Fiske, 1959). The committee recommends the principle of convergent validity as a means for SSA examiners to make sense of all the information evaluated for diagnostic decisions about mental retardation. In clinical practice, information is collected and evaluated over broad domains of functioning, using multiple methods of gathering data, multiple sources for that information, and multiple settings (e.g., Gresham, 1991). If the information is generally consistent with a particular diagnostic decision, such as mental retardation, that decision is made based on this confirmation. If, however, there are several elements in the overall array of information that

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

are inconsistent with such a diagnosis, the decision is not confirmed or—and this is important—further investigation is undertaken to explain discrepancies.

Inconsistent Information

Many individuals with legitimate diagnoses of mental retardation will present clinically with one or more elements of information that are inconsistent with the diagnosis. Many times, on further examination, the inconsistent information will derive from a mistake or distortion of measures of adaptive or intellectual functioning—for example, the existence of high scores from an adaptive behavior inventory with little or no ceiling for a young adult. In other cases, a particular respondent or performance in a specific setting may not be consistent with the diagnosis of mental retardation. Inconsistent information must be investigated thoroughly in order to avoid the harmful consequences of false positive or false negative decisions. Further investigation may take many different forms, including more extensive interviews with the client and significant others, additional assessments of adaptive or intellectual functioning, or follow-up contacts with personnel in other agencies who may or may not have made a diagnosis of mental retardation.

Information from Other Agencies

As noted previously in this report, mental retardation diagnoses are made for many purposes by many different agencies, including schools, law enforcement, and health care agencies. Different agencies use different diagnostic systems and classification criteria, making diagnostic disagreements among agencies perfectly legitimate. Moreover, the standards used by some agencies, public schools in particular, differ markedly from state to state and, occasionally, from district to district within states.

Several sources of information confirm the increasing reluctance of school officials to make a diagnosis of mental retardation. First, the

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

TABLE 5-5 Changes in Prevalence of Learning Disabilities and Mental Retardation over the 1976-1999 Period in Public School Special Education Programs

 

1976-77

1998-99

Change

% Change

Learning disabilities

797,213

2,861,333

2,064,120

260%

Mental retardation

969,547

613,207

–356,340

–36%

NOTE: All data are from the 1978 and 2000 Annual Reports to Congress by the Office of Special Education Programs, U.S. Department of Education.

prevalence of mental retardation in schools has declined substantially over the last 25 years. It is extremely unlikely that all of the decline is attributable to a truly lower prevalence of mild mental retardation. The decline in mild mental retardation is paralleled by a corresponding and substantially greater increase in learning disabilities (see Table 5-5). According to the Office of Special Education Programs child count data (U.S. Department of Education, 2000), prevalence of learning disabilities has increased by 260 percent while mental retardation prevalence has declined by 37 percent since the 1976-1977 academic year, when these data were first collected. These changes are even more impressive because they occurred during a period when children and youth with moderate, severe, and profound mental retardation gained access to the public schools for the first time in many states and districts. Although the child count data do not differentiate levels of mental retardation, it is highly likely that the decline in mild mental retardation has been even greater than the overall decline in mental retardation, simply because those with more severe mental retardation are more obviously impaired in many areas and are therefore more likely to be correctly diagnosed with mental retardation.

The declining prevalence of mental retardation in the public schools is even more complex because it varies significantly across the states. The mental retardation prevalence among states varied by a

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

factor of three in the 1998-1999 data; that is, the highest prevalence reported by any state was three times higher than the lowest state-reported prevalence. Moreover, 28 states reported public school prevalence of less than 1 percent of the student population, meaning that some students with mild mental retardation are either not being placed in special education or are in special education because of other diagnoses, such as learning disability.

Studies in California confirm both the reluctance of school professionals to confer the diagnosis of mental retardation and the willingness to use other diagnoses for children with characteristics that meet mental retardation classification criteria (MacMillan, Gresham et al., 1996). This leads to concerns about the continued viability of the mild mental retardation diagnostic construct in special education and schools (MacMillan & Reschly, 1996; MacMillan, Siperstein, & Gresham, 1996). The California studies indicate that staffing teams simply refused to diagnose students as having mild mental retardation even when IQ, achievement, and adaptive behavior data clearly pointed to that diagnosis. The degree to which these results generalize to other states is unknown, although the large decline in children diagnosed as having mild mental retardation suggests that the reluctance among California school psychologists and special educators to use this diagnosis may exist in many other places as well.

The presence or absence of a diagnosis of mental retardation from another agency, especially from public schools, should neither confirm nor disconfirm an SSA diagnosis of mental retardation. Information from other agencies should be evaluated by SSA examiners, but should not be regarded as definitive. Although the official diagnoses used in other agencies are often not applicable to SSA eligibility determination, such information as direct measures of skills and records reflecting overall adjustment can be highly useful. Attempts should be made to obtain records from other agencies with that information interpreted by persons familiar with the functioning of the agency. Information from schools that is particularly relevant to mental retardation diagnoses includes measures of skills such as standardized test results,

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

teacher-assigned grades, history of retention in grade, curriculum track pursued, and participation in special education programs, regardless of diagnosis.

CONCLUSIONS AND RECOMMENDATIONS

Broad consensus exists about the appropriate cutoff criteria for intellectual ability in mental retardation diagnosis: A cutoff score of approximately two standard deviations below the mean is well accepted in most settings. A similar consensus does not exist, however, regarding the appropriate cutoff for adaptive behavior. The use of a stringent adaptive behavior cutoff like that used for intellectual functioning would sharply reduce the number of people with IQs below 70 eligible to be considered for a diagnosis of mental retardation. On the basis of the committee’s knowledge of individuals with mental retardation as well as the relevant research literature, this outcome is undesirable. We, therefore, propose formal adaptive behavior assessment as part of a comprehensive evaluation for individuals with or suspected of having mental retardation and cutoff scores that are more lenient than those widely used for intellectual functioning.

Diagnostic decision making in mental retardation needs to be based on a comprehensive evaluation that uses multiple methods of collecting data from multiple sources across multiple settings. We support a principle of convergent validity as a means to interpret a broad variety of information. As discussed in Chapter 3, in the rare case in which a composite IQ is suspected to be spurious, the composite score should be ignored and either an appropriate part score (as described in Chapter 3) or other methods should be used to confirm or disconfirm a diagnosis of mental retardation. Diagnostic decisions should always be based on the preponderance of evidence, not just one numerical score.

Finally, the need for more research, particularly on the measurement of adaptive behavior, is crucial to improving decisions about mental retardation eligibility. Adaptive behavior assessment is not as well

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

developed as intellectual assessment, although improvements over the last decade have occurred.

On the basis of its review, the committee makes the following recommendations.

Recommendation: A diagnosis of mental retardation must be based on high-quality assessments of intellectual and adaptive functioning that meet the following criteria:

  • A broad variety of information on adaptive behavior and intelligence should be collected, including data on performance in different settings, from different sources, and using varying methods.

  • Comprehensive, multifactored measures of intelligence and adaptive behavior should be used in mental retardation eligibility determination. Brief, unidimensional measures or short forms of comprehensive tests should not be used.

  • The principle of convergent validity shall be applied in eligibility decisions about mental retardation eligibility. Information that is inconsistent with a diagnosis of mental retardation should be recognized, evaluated, and explained in the overall diagnostic decision.

  • Assessments must be conducted by people with appropriate education and experience for the kind of instrument used and the nature of the eligibility decision to be made. People conducting intellectual assessments must meet publishers’ requirements for Class C instruments.

  • Measures of adaptive and intellectual functioning should be carefully selected and interpreted in order to minimize the negative effects of low validity, low reliability, floor and ceiling effects, and steep item gradients.

  • The norms for measures of adaptive and intellectual functioning must be suitably contemporary. Use of outdated norms or previous editions of recently restandardized measures is not

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

acceptable. The norms for intellectual measures should be no older than 12 years because of the deterioration of the normative standards over time.

  • Decisions about mental retardation eligibility should be made by people with appropriate preparation in the areas of mental retardation and other disabilities and disorders, measurement of intellectual and adaptive functioning, knowledge of human development, and the influence of context on behavior.

The committee’s recommendations reflect concerns about the quality of the available evidence as well as the necessity to provide reasonable guidance to people making eligibility decisions regarding a diagnosis of mental retardation. The committee concludes that more research on the measurement of adaptive behavior with children and adults is urgently needed, including investigation of classification agreement. The following recommendation reflects these concerns.

Recommendation: Federal agencies, including the Social Security Administration (SSA), should fund studies to evaluate the accuracy of program eligibility decisions and foster research on adults with mental retardation, including their adaptive behavior. The research funding should include investigations of multimethod techniques for the assessment of job-related skills, social adaptation, health, and well-being. In addition, relevant epidemiological studies and research on the accuracy of diagnosis of mild mental retardation are essential to inform policy and decision making.

  • SSA should evaluate the consequences of implementing the committee’s recommendations in the context of public policies and economic conditions, reporting findings to the public within five years.

  • Since improved accuracy in eligibility determination depends more on improved measures of the key dimensions of mental

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
×

retardation than on adjusting cutoff scores, the committee recommends research on improving measures, especially adaptive behavior assessment, and on methods to combine information on adaptive and intellectual functioning in making eligibility decisions based on a diagnosis of mental retardation.

  • SSA should make available for use by legitimate researchers tapes of Supplemental Security Income and Disability Insurance program utilization, comparable to public-use tapes available for Medicaid program utilization.

  • SSA should link its data on individual benefit awards to other agency data on health care and service costs for those same beneficiaries.

  • SSA should examine data on eligibility determination procedures across its 10 districts, in order to discover if implementation of classification policies is consistent or varies regionally.

Suggested Citation:"5. The Relationship of Intelligence and Adaptive Behavior." National Research Council. 2002. Mental Retardation: Determining Eligibility for Social Security Benefits. Washington, DC: The National Academies Press. doi: 10.17226/10295.
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Current estimates suggest that between one and three percent of people living in the United States will receive a diagnosis of mental retardation. Mental retardation, a condition characterized by deficits in intellectual capabilities and adaptive behavior, can be particularly hard to diagnose in the mild range of the disability. The U.S. Social Security Administration (SSA) provides income support and medical benefits to individuals with cognitive limitations who experience significant problems in their ability to perform work and may therefore be in need of governmental support. Addressing the concern that SSA’s current procedures are consistent with current scientific and professional practices, this book evaluates the process used by SSA to determine eligibility for these benefits. It examines the adequacy of the SSA definition of mental retardation and its current procedures for assessing intellectual capabilities, discusses adaptive behavior and its assessment, advises on ways to combine intellectual and adaptive assessment to provide a complete profile of an individual's capabilities, and clarifies ways to differentiate mental retardation from other conditions.

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