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EXECUTIVE SUMMARY This study provides an in-depth analysis of what has happened to doctorate completion times from 1967 to 1986, an aggregate time-series data base, and a model that explores some of the factors that cause an elongation of total time to the doctorate (TTD). The model looks at the effects of five types of variables: family background characteristics, student attributes, financial aid, institutional environment, and market forces. Using data from the Doctorate Records File and the Survey of Doctorate Recipients maintained by the Office of Scientific and Engineering Personnel of the National Research Council, a model is developed and tested to explain changes in TTD and in the several component parts of the TTD measure. The model is applied to 11 scientific and engineering fields: chemistry; physics and astronomy (P&A); earth, atmospheric, and marine sciences (EAM); mathematical sciences (including computer and information sciences); engineering; agricultural sciences; biological sciences; health sciences; psychology; economics; and all other social sciences. Findings Trends it' TTD The analysis finds that~l~lD, defined as the time lapse from the year that a student receives an undergraduate degree to the year that the doctorate is completed, initially decreased in the 1960s and then rose swiftly in the 1970s and 1980s. As a consequence, it now takes longer to complete a doctoral degree than at any previous time in this century. Mean Lyle increased in each of the 11 fields in this study, ranging from a low of 0.3 years in economics to a high of 2.8 years in the health sciences. Increases in excess of two years were experienced in mathematics, psychology, and social sciences. Moreover, a double-digit percentage increase in l-l i, was experienced in all but biosciences and agricultural sciences. TTD increased even in fields where the time lapse to the doctorate was already quite long. For example, the average TTD in the health sciences was 10.5 years in 1967 and 13.3 years in 1986; in the social sciences it was 10.6 years in 1967 and 12.9 years in 1986. The evidence also

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suggests that student completion times are becoming more concentrated around the mean. The rise in TTD is occurring at a nonlinear rather than a linear rate. In chemistry, physics and astronomy, and engineering, TTD has been rising at a decreasing rate. However, in the eight other fields examined, TTD has been rising at an increasing rate and is thus cause for greater concern. Trends in Components of TTD TTD can increase because students spend more time registered as students or because interruptions on the path from a bachelor's to a doctorate cause them not to be enrolled in school. Analysis of components of TTD indicates that most of the increase is attributable to the increase in registered time to degree (RTD) that is, TTD less the time prior to graduate school entry (TPGE) and time not enrolled in graduate school (TNEU). In all of the 11 fields examined, RTD has increased substantially since 1967, accounting for most of the change in TTD in every case. Where RTD did not account for the total increase in TTD, interruptions in studies were the most frequent cause for lengthening of TTD. Delays in starting graduate school were an important additional explanation in only one field, health sciences. Modeling TTD Careful review of the relevant literature reveals five distinct but related lines of inquiry that bear on the development of a model of the causes of the rise ~in- TTD. These lines of inquiry include the determinants of persistence and attrition, students' educational aspirations, the factors affecting enrollment in college, the role of expected returns and their effect on the decision to enter graduate school, and the literature on TTD. Several variables are consistently identified as affecting student choice: financial aid, whether the student is self- supporting, immediate background characteristics (rather than past background), quality of the undergraduate and graduate college, and differences in expected earnings and changes in market conditions. The model used in the present study consists of five vectors of variables: family background characteristics, student attributes, tuition and financial aid, institutional environment and policies, and market forces. The model is estimated in both linear and nonlinear form and with two variants. Variant 1, the "common variables" model, includes the same variables for each field and is designed to determine whether a consistent set of variables is important in each field. Variant 2, the "unique variables" model, allows the number of variables in the explanatory equation to vary so that only those that are statistically significant are included in each final regression equation. For each field, regression equations are estimated using the 1967-1986 years as the units of analysis. Separate analyses made for the TTD and RTD variables produce the following results: 2

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Results For TTD: Student characteristics and market forces are the key variables that affect TTD. However, the explanatory variables differ by field and by equation specification. The variable that most consistently explains rises in TTD is age at time of entry to graduate school. This is statistically significant in 9 of the 11 fields studied. Unfortunately, the model does not enable one to determine whether this variable relates to physical or intellectual effects of age (e.g., it takes older persons longer to learn) or whether its effects on TTD operate primarily because students who start later have a longer TPGE. Among the market force variables, the salary ratio of doctorates 10 years after the doctorate to the salary of recent doctorates is significant in chemistry and EAM (using the common variables linear model) and in agricultural sciences and psychology (using the unique variables model). The salary level of doctorates 10 years after the degree is statistically significant in economics and social sciences. Among the family background variables, female gender is statistically significant in EAM and marine sciences. Type of institution attended affects AD in some fields and quality of undergraduate institution (but not quality of graduate institution) is usually statistically significant. In psychology, a 1 percent increase in the percentage of a doctoral cohort with a bachelor's degree from a top 70 institution is associated with a 0.1 year decrease in 171~. Results for RTD: No one variable is consistently large enough or consistently statistically significant enough across fields to explain the observed increase in RTD in all fields. Instead, different combinations of variables explain the rise in RTD in each of the 11 fields. In those equations where age is statistically significant, it tends to have a large impact on RTD. In the common variables log model, for example, the coefficients of the models range from 0.9 years (health sciences) to 6.4 years (social sciences). Since RTD is purged of TPGE, age does not act as a measure of late arrival at graduate school and, hence, its meaning is somewhat clearer in these regressions. Perhaps in part as a consequence, the age variable is not statistically significant in as many fields in the RTD equations (4) as it is in the TTD equations (9~. Financial aid that reduces student reliance on outside employment can make a difference in terms of RTD, and the type of aid is important in determining RTD as to which type of aid is most likely to reduce RTD, the models do not permit a single statement that applies to all fields. Instead, the effects of financial aid are highly field-specific. For example, a 1 percentage point change in federal support reduces RTD by 0.06 percent in EAM, 0.11 year in biological sciences, 0.23 in health sciences, and 0.09 in economics. Teaching assistantship (TA) support reduces RTD in EAM but increases it in biological sciences; and research assistantship (RA) support reduces RTD in math but raises it in biological sciences. The effects of particular forms of aid warrant further exploration. In the fields of chemistry, mathematics, and economics, increases in the percentage of students with baccalaureates increase RTD in the common 3

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variables log model. Changes in market variables, particularly in the unemployment rate and the salary ratio, also affect RTD. Specifically, in the common variables log model, increases in the unemployment rate of 4-year college graduates tend to reduce RTD. A 1 percentage point change in the variable causes a 0.07 decline in 'l-l'D in EAM and a 0.02 decline in biological sciences. In the unique variables model, an increase in the percentage of new graduates seeking (but not yet finding) a position prior to graduation raises RTD in the biological sciences. Finally, increases in salaries for those who already hold doctorates, relative to increases in the salaries of new doctorates, have the effect of reducing RTD. This phenomenon is found primarily in the unique variables model and primarily in chemistry, mathematics, biological sciences, health sciences, psychology, and economics (Note: Several ratios are constructed with different years in the denominator, and which ratio is statistically significant is field specific). Additional research on the sources of the rise in 1TD is warranted. The process of acquiring a doctorate is a complex one that involves a variety of decisionmakers. No one set of unique factors adequately explains the rise in TTD and RTD. Moreover, our findings lack robustness with respect to the determinants of TTD and RTD. This may, in part, be attributable to lack of sufficient independent variation in the doctoral cohort's average annual time- series data for the period 1967-1986. For example, although time-series analysis did not indicate large and uniformly statistically significant effects for the student aid variables, simple cross-tabulations for 1986 and 1987 show that students reporting primary support from "own" earnings take, on average, over five more years to complete the doctorate than those with external financial aid. While this ~ difference may be attributable to differences in the abilities and knowledge of recipients and non-recipients, we cannot rule out the possibility that a study of individuals would produce a stronger role for the financial variables. It may well be that alternative units of analysis will produce different andior more consistent results than those presented here. Conclusions The data in this report indicate that students in general now take longer to complete their doctorates than at any previous time in this century. This exploratory analysis of the factors underlying these trends revealed a complex process that is affected by a variety of factors including availability of student support, labor-market conditions, sociodemographic characteristics of the degree recipients, and characteristics of both undergraduate and graduate degree-granting institutions. As noted earlier, no one of these factors consistently explained the pervasive upward trend that was found. Thus, more effort will be required to enhance understanding of this process. Moreover, the authors did not explore the consequences of these trends, although the rising trend in AD found in this study might lead to unacceptably 4

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high levels in some fields. First, increases in 1lD lengthen the amount of time required for the supply to respond to any shifts in market demand. Such lags in supply responsiveness are costly to society. Second, increases in 11D may raise the costs and lower the returns to investment in doctoral training with possible consequences for career choice decisions of potential doctoral students. Other things equal, higher costs and lower returns can discourage students from pursuing training at the doctoral level. In addition, given the decision to pursue such training, increasing 11D may encourage some students to drop out before completing their degrees. Finally, lengthening TTD may, other things equal, reduce productivity by reducing the number of years spent by cohorts of newly produced degree-holders working as doctorates. Little is currently known about these possible consequences, but they are potentially serious enough to merit further attention. s

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