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6
RATIONALE AND RECOMMENDATIONS FOR EARLY ACTION
INTRODUCTION
As indicated in Chapter 5, improvement in the data collection, processing,
and reporting methods of the Nationwide Food Consumption Surveys (NFCS) and
the National Health and Nutrition Examination Survey (NHANES) can be advanta-
geous both in the uses of the core (NFCS and NHANES3 survey data bases inde-
pendently and in their conjoint use, e.g., in a wider system of nationwide
food and nutrition monitoring. Implementation of the recommendations pre-
sented here and in Chapter 7 will permit the surveys to be used more widely
and more effectively.
The Committee has evaluated sugges Lions from data us er s regarding possible
modifications of the survey instruments. Survey design modifications that
increase the specificity of the data obtained (e.g., incorporation of food-
item brand names, identification of both physical and logistic impediments to
food intake, and sub jects' -use of medications that might interact with
nutrients ~ were suggested during workshop and symposium discussions. Although
these suggestions would be advantageous to some users, the Committee's recom-
mendations are based on giving highest priority to changes that will benefit
the data user community at large . The Committee also cons idered potential
cost constraints in developing its recommendations. Recommendations for early
action are discussed in this chapter and those expected to require longer-term
implementation are discussed in the next chapter.
The recommendations of the Committee are related primarily to modifica-
tions in survey design, food intake methods, and information on the compo-
sition of foods, that is, information on what people are eating and infor-
mation on who is eating that food. More specifically, the recommendations on
food intake survey methods concern continuous collection, processing, and
reporting of survey data, continued collection of replicated data, and
similarity in methods of data collection. The recommendations on information
on the composition of foods concern expans ion of the qualitative and quan-
titative data on the composition of foods, use of standardized tables on the
composition of foods, and use of standardized codes for reporting the food
ingested. The recommendations on population data concern sampling similarity
and the use of compatible sampling frames for selecting survey subjects.
Implementation of these recommendations will be most helpful to those
us ing the survey data to assess dietary intake of various food components of
biologic importance. In addition, these changes can also increase the utility
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of survey data in designing or modifying feeding programs for population
groups; developing nutrition education~programs, nutrition guidance, and
dietary recommendation materials; and developing new programs in agricultural
production and food processing to yield products useful in food and dietary
modifications .
SURVEY PURPOSES AS GUIDES
The purposes of the separate surveys provide a useful perspective for con-
sidering agency or interagency coordination of Committee recommendations.
The NFCS serves as the major national focus for collection of food con-
sumption and dietary intake data that address the question of who is eating
w _ . All other uses of the data are derived from the answers to these funda-
mental questions . Furthermore, it is necessary that NFCS data and reports be
provided to users promptly and in a format that fosters compatibility and com-
parability with other data bases.
The purposes of the NHANES are related to measurements of the prevalence
of disease states and health conditions. The dietary component of the NHANES
is complementary to its fundamental purposes. The role of the NHANES data is
critical for emerging uses of survey data, particularly uses concerned with
epidemiologic and public-health applications. These uses require that the
NHANES data base be comparable and compatible with the NFCS and that infor-
mation be reported in a timely fashion.
Some of the Committee recommendations discussed in this chapter are
related more to dietary intake data than to data on the prevalence of health
conditions and disease states. Given the different purposes of the surveys,
the Committee believes that the U.S. Department of Agriculture (USDA) is the
likely agency to.lead in implementing several of these recommendations. The
Committee recommends that USDA serve as the lead federal agency for survey
standardizations dealing primarily with the food-related aspects of federally
funded food consumption and dietary intake surveys. Where health conditions
and disease states would be a major focus for survey modifications, the Com-
mittee recommends thee the Department of Health and Human Services (0HHS)
serve as the lead federal agency.
Given the different purposes and data collection methods of the surveys,
recommendations are not always the same for both surveys. The Committee's
recommendations are based on consideration not only of both the independent
ant the conjoint current uses of the survey data, but of emerging uses for
data. Some recommendations on survey modifications that would foster more
timely collection and reporting of the survey results are intended to serve
future data users better without compromis ing currently essential uses .
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RECOMMENDATIONS ON SURVEY DESIGN
Data from the NFCS and the NHANES have many and varied uses. Given the
variety of current and emerging uses for these data, it is difficult to de-
velop a single set of recommendations that will serve the needs of all data
us ers .
CONTINUOUS EVALUATION PROCESS
While accepting the realities of continuing independent but mutually com-
patible surveys, the Committee recognized the merit of a continuing consider-
ation of the desired features of a composite single survey. As discussed in
Chapter 5, the Committee developed a systematic approach to examining issues
of definition of data needed and of requisite precision and reliability of
da ta ~ Append ix A) .
The Committee found its approach useful and
recommends that it be made an on-going process in the
continuing rev few and evaluation of the separate
surveys, their purposes and their design.
CONTINUOUS SURVEYS
A consistent need of all data users is the timely reporting of survey
information. Thus, implementation of changes in food intake methods that
would provide for timely reporting of data and other survey results would be
beneficial to all users of food consumption and dietary intake surrey data.
The core surveys have his torical ly been conducted at intervals . NHANES I
and II were conducted in 1971-1974 and 1976-1980 and the two mos t recent NFCS
more than 10 years apart (1964 and 1977-1978~.
Data collection for the 1977-1978 NFCS took a year. NFCS methods re
uire data collection from a large, representative sample of U.S. households
and persons in those households. The large volume of data collected results
in a large volume of data to be coded and processed. In the view of the Com-
mittee, a fundamental barrier to timeliness in reporting survey data is the
size of the data collection -- about 15,000 households and about 30,000 indi-
vidual~. This collection phase has the potential for "input overload" with a
backlog of data in the initial survey process . Redes ign of the Individual
Dietary Intake component of the NFCS to collect and report data continuous ly
would help to overcome this barrier to timely data collection and reporting.
USDA has proposed a continuous system to monitor and report on the food
consumption and dietary intake of women aged 20-50 and their children; other
high-risk groups, such as the elderly, might be added to the panel. This
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system of data collection would provide the data base for a series of annual
reports . But, for ache same cos t, the sample of persons interviewed each year
will be much increased if they are visited only once. Therefore, the Com-
mittee does not believe that the panel approach is as likely to be as
efficient as a continuous sampling to detect changes in food consumption pat-
terns of subsections of the population (e.g., in consequence of recent unem-
plo~rment) that cannot be well identified beforehand.
The Committee recommends redes ign of the
Individual Dietary Intake component of the NFCS.
Instead of an intermittent 1-year survey of a large
sample, the Committee sugges ts an annual survey that
would distribute the total sample over a number of
years. -A design that provides for the collection and
processing of data from 20% of the full sample per
year has been suggestedl3. Addition of data
accumulated in the preceding 4 years to the data
Cal lee ted during a current year would provide data on
the total sample. This design would reduce the
problem of input overload to a minimum.
The data collected in the Committee's proposed
continuous Individual Dietary Intake survey should
include the detailed population and socioeconomic
descriptors that adequately and precisely identify the
survey subjects and their household characteristics,
as well as their food consumption and dietary intake.
Similar considerations about "input overload" pertain to the NHANES. Data
for the 1976-1980 survey covered 20,000 individuals, and some of the data col-
lected are still not available for analysis in 1984. The next NHANES is
scheduled for 1987.
The Committee recommends redesign of future
NHANES. Instead of intermittent surveys, the
Committee suggests a survey that would distribute the
total sample over 5 years. Collection and processing
of data from 20% of the full sample per year would
permit addition of data accumulated in the preceding 4
years to be added to the data Cal lected during the
current year, to provide data on the total 5-year
~ample. This design would reduce the problem of input
overioat to a minimum ant would permit a moving 5-year
average to be reported every year.
CONTINUOUS DATA PROCESSING AND REPORTING
A common user need identified by the Committee is for data to be made
available as soon as possible after being collected. To be used effectively,
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data on foot consumption and dietary intake should reflect information that is
current, given the limitations of survey design.
A continuous data processing and reporting system would probably involve
calculations updated annually on the basis of tats accumulated in each given
year ant the preceding 4 years (i.e., a 5-year moving average). Annual
would also be possible, e.g.,
~~ of necessity,
analyses over a period of years would also De posezole, e.g., over a '-year
period. This system of moving averages would, of necessity, involve some
data several years old. However, the advantage of providing users with con-
tinually updated data is that it largely removes concerns about the incor-
poration of otter data in the moving average. The availability of this
updated information, coupled with information on the foot consumption and
dietary intake of subjects, would make such data more widely and effectively
used.
Along with implementation of continuous data
collecting systems for the Individual Dietary Intake
component of the NFCS and for the NHANES, the
Committee recommento the implementation of continuous
systems for processing data, releasing data tapes, ant
reporting. Dmplementation of a continuous system
would result in the more efficient and timely
collection, processing, ant reporting of survey data
on food consumption ant dietary intake.
COLLECTION OF REPLICATED DATA
The core surveys yield statistical data on food consumption and dietary
intake of two general types: data related to group mean intake across popu-
lation groups and data relates to intake ant distribution of intake within
population groups.
The NHANES collects a 24-hour recall of dietary intake and thus con-
tributes population late on group means across population groups. With NHANES
data, the estimated mean nutrient intake (e.g., iron, calcium, or fat) can be
established for population groups defines by sex, age, race, income, or other
selected variables.
The Individual Dietary Intake component of the NFCS, however, collects
3-day dietary intake data ant thus can provide two types of information: data
on group means (as above) and, more important, data that can be used to derive
estimated of the distribution of intakes among individuals within groups. The
3 individual days of intake data collected by the NFCS probably provide a
minimum of data points needed to estimate the partitioning of '~etween-
subject" and "day-to-day" variances. The '~etween-subject" variance is a
descriptor of the distribution of intakes within the population group (defined
by sex, age, race, income, and other variables). This '~etween-subject"
distribution is what is neetedl6~24 to address questions relates to the
prevalence of high or low dietary intake of given food components. Thus, the
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3 individual days of dietary intake information, rather than the 3-day mean,
obtained from NFCS tata collection covit provide partic- ularly important
information. However, the data should be collected by the same method for
each of these three days. This is not the present practice where recall data
in used for one day and diary data for the other two.
Both types of information -- variability across population groups (NHANES
and NECS) and variability within population groups (NFCS) -- are important for
many uses of the separate survey data bases. They take on particular impor-
tance when they can be linked to additional data sources for nationwide food
and nutrition monitoring.
The Committee recommends that USDA, at a minimum,
continue to collect replicated data on food
consumption and dietary intake of individuals, e.g.,
that USDA maintain, at a minimum, the collection of
3-day intake information used in the individual intake
phase of the 1977-1978 NFCS. This replicate data,
however, should be collected by a single method.
The Committee notes that the minimal number of replicate days required to
provide reliable estimates of the distribution of intakes within a population
group depends on group size and the day-to-day variability of intake. It also
recognizes that questions of comparability of dietary methods used in col-
lecting information and of seasonal and other effects warrant consideration.
Existing data bases are not adequate for this purpose. However, implemen-
tation of a system of collection of additional replications, distributed
across a year, coupled with careful statistical analyses could provide
extremely important information for the refinement of survey design and
improvement of interpretation.
USDA already has plans for replications of data collection from the same
individuals during a 1-year period. The Committee endorses this as a method-
ologic study, even though not recommending it as a continuing survey system.
Because of the need for statistical analysis of
intraindividual variability, the Committee supports
USDA's proposed plan for the repeated surveying of
individuals over a 1-year period. The Committee
believes that this will allow needed statistical
analyses whose results will, over the longer term,
permit determination of the best data collection
procedures.
The NHANES also needs replicate data, because the dietary data are used to
investigate the effects of diet on health. Knowledge of the variability of
diet in an individual is necessary for other analyses. Where the NHANES
already does other replicate subsampling, addition of 24-hour recall replicate
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sub~amples is necessaryi63~7~27328 to estimate intraindividual variability
for interpretation of regression analyses that use dietary information as a
determinant29 in health-related analyses.
Expansion of the NHANES to permit collection of
replicate dietary intake data in a subeample ant thus
to address currently unresolved statistical concerns
about intraindividual variability is ai80 encouraged.
This replicate data collection can be done within the
current survey design and time constraints imposed by
current use of the mobile examination unite, inasmuch
as the mobile examination units remain in a single
locality for about 6 weeks. Within that Midweek
period, some subjects can be reinterviewed.
RECOMMENDATIONS ON FOOD INTAKE METHODS
Usere identified other needs for data that have implications for food
intake methods and information on the composition of foods. Many of these
needs call for data that answer questions broadly related to what is being
consumed. Table 4-2 identifies many of there questions.
Several of the tats needs identified by users can be met by changing the
methods for surveying food intake. Committee recommendations for modifying
these methods are made in response to those user needs. In some instances, a
modification suggested by the Committee involves only one of the core surveys;
in other instances, the Committee has recommended joint action to effect
common changes in food intake methods.
CO=ON DIETARY RECALL METHODS
If dietary data are to be interpreted adequately, reliable estimates of
the distributions of usual intake within the population or population groups
are needed. Such estimating requires planned replication of 1-say dietary
intake data collection or, as recommended earlier, continuation of the USDA
process of collecting multiple days of intake data. When couplet with appro-
priate statistical analysis, such data sets can yield the required estimates
of the dis tributions of usual intake. The combination of this survey des ign
feature, an NFCS sample larger than that of the NHANES, its improved repre~en-
tation of the population, and the increased opportunity for dividing the popu-
lation into groups of particular interest has let the Committee to emphasize
the role of the USDA data- base as the primary dietary data base.
The I-day intake (24-hour recall) data bane of the NHANES can be uset to
obtain reliable estimates of the average usual intake (but not distribution of
intake) of population groups, provided that the groups are large enough. For
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some analyses, such as those in which groups are classified on the basis of
other criteria and group mean intakes are compared, either data bane could be
used. Indeed, that is a current practice .
For some applications, it is pose ible to link findings across the two
surveys by using mean and variance of dietary intake of defined groups to
confirm that the groups are comparable between the two survey data bases.
Such confirmation lends greater confidence when data from the surveys that do
not overlap are linked (e.g., linking NHANES health or biochemical data to
NFCS household descriptors, economic tata, or other traits characterizing
groups). In the context of this report, the dietary corroboration is impor-
tant, because nutritional, and hence dietary, problems are the focus of the
analyses discussed here.
The Committee has received many indications that the approach discussed
above may not yet be possible. Even when groups with similar general charac-
teristics are selected in the NFCS and NHANES populations, there are strong
reasons to believe that agreement of mean dietary intake would not be seen --
not that it toes not exist, but rather that the computed intakes are likely to
differ. Some of the reasons are related to the differences in coding pro-
cedures ant in data bases on the composition of foods . In addition, the two
surveys differ in food intake data collection methods and that this might
contribute to dif ference~ in es timated intakes .
As discussed earlier, the 1977-1978 NFCS methods incorporated a 24-hour
recall and a 2-day record to collect information on 3 days of individual
dietary intake. The 1976-1980 NHANES methods included a 1-day recall and, for
other reasons, a foot-frequency questionnaire technique. Thus, in part, the
methods -- with inclusion of 1-day recall -- are similar, although the actual
procedures us et for this common element were not standardized across the
surveys. In the judgment of the Committee, standardization of some of the
core elements with this common technique could foster comparability and facil-
itate the cross-linking of information. Where feasible, Standardization of
some of the methods used to collect the 24-hour dietary recall information
would increase the utility of both surveys without contravening the internal
purposes of either.
The Committee recommend. that core elements of
the methods used for the 24-hour recall in the two
surveys be standardized. This would also include both
the standardization of interviewing techniques and the
format of interviewing subjects. As discussed later
in this report, ~ tandardization should also include
the coding of food intake data and the use of common
data bases on the composition of foods.
The Committee notes that USDA has previously
commissioned studies to evaluate food intake methods.
Results of these studies may lead to modifications of
the 24-hour, as well as dietary record, data
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collection procedures. In commending USDA for this
continuing effort to improve food intake methods, the
Committee urges that any changes in core elements of
the 24-hour component be implemented uniformly across
the two surveys. The Committee, using the survey
purposes as guides, suggests that USDA serve a lead
role in this regard, but emphasizes that the logistic
implications of changes should be considered in the
context of both surveys.
INFORMATION ON D IETARY SUPPLEMENT USE
Both the NHAl7ES and the NFCS obtained limited information on the use of
dietary supplements (e.g., vitamin or vitamin~mineral preparations). However,
neither survey collected such information in the detailed manner that was used
to collect other food consumption and dietary intake data.
A recent report on the use of dietary supplements30 indicated that about
43X of people surveyed were using vitamin or vitamin-mineral supplements. But
such data are no substitute for data collected as an integral part of a food
consumption and dietary intake survey. Thin telephone survey report serves to
point out that future surveys should collect better information on this source
of nutrients. More detailed data, collected within the context of a food con-
sumption and dietary intake survey, can show how frequently supplements are
being ingested ant when and will provide a more realistic perspective on the
nutrients present in the dicta of survey subjects.
In anticipation that core elements of dietary
intake questionnaires will be standardized, the
Committee recommence that the two surveys include
questions to obtain information on the use of dietary
supplements. There possible, brand names and
quantities ingested or other qualitative and
quantitative information (e.g., potency), should be
~ought.
Because of the poss ible complexity and
multiplicity of information that could be obtained,
the Committee suggests that as interagency working
group be convened to determine the nature ant wording
of the core questions used to obtain information on
the use of dietary supplements. With the survey
purposes as guides, given that the thrust of this
e f fort is dietary, the Committee recommends thee USDA
serve as the lead agency in convening the sugges ted
working group.
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D ISCRET IONARY I) IETARY COMPONENTS
. .
Although water, alcoholic beverages, sugar, salt, ant fat are important
dietary components, their intake is difficult to estimate. In part, this is
related to their discretionary use in diets (e.g., sugar and salt used at the
table ant trimming or not trimming fat) and the variability in their use --
both between persons and in one person's own behavior.
Both the NFCS and the NHANES have obtained some information on discre-
tionary dietary use of alcoholic beverages and salt. However, data users have
expressed a need for increased quantitative information on the use of discre-
tionary dietary components.
Alcohol, sugar, and fat are discretionary sources of dietary energy. The
estimation of their contribution to total dietary energy (i.e., what is con-
sumed) is important for all data uses. Quantitative estimates of fat, sugar,
ant salt consumption are particularly important for public-health uses of the
data. Water is an important component of the diet and can be a source of
nutritionally essential trace minerals.
The Committee believes that it will be difficult to develop core com-
ponent~ for the survey questionnaires that will result in improved estimates
of discretionary dietary components. For some components, special surveys may
be required. Nevertheless, the Committee expects that the addition of more
detailed and reliable quantitative information on discretionary dietary com-
ponents is an important modification for future surveys.
The Committee recommends that USDA and DHHS
convene a joint working group to develop improved
techniques for determining the consumption of
discretionary dietary components. The Committee
suggests that this review include considering the
utility of special surveys for determining the
consumption of these components and, alternatively,
the utility of adding core components to the existing
surveys that better measure the consumption of
discretionary dietary components.
FOOD-FREQUENCY QUESTIONNAIRE TECHNIQUE
A food-frequency (tietary-frequency) questionnaire technique is part of
the design of the NHANES. These questionnaires are uses, often in epidemi-
ologic studies, as a means of acquiring information on the usual pattern of
general dietary intake of specific foots or nutrients over a long period. The
information recorded includes whether foods in various groupings -- such as
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milk, meat, fish, eggs, fats ant oils, legumes and nuts, cereals, fruits,
vegetables, and alcoholic beverages ~ have been consumed in the past ant
number of times each food was consumed daily or weekly.
It has been suggested that this technique for collecting ant reporting
information on a survey sub ject to ''usual" food intake be incorporated into the
NFCS. However, the Committee is not convinced that the food-frequency tech-
nique has been developed to its full potential, partly because adequate vali-
dation studies have not been done with typical American cultures.3 More
importantly, there has been inadequate recognition of the need to define end
use of the data before design of the instrument. When this is done, the food-
frequency technique can be an appropriate tool32~33 for specified purposes.
The Committee recommends review of the use of a
food-frequency ques tionnaire technique . Potent ial
modifications to allow some quantification of
individual intake over time should be explored.
Adequate resources should be made available to test
the validity and cost effectiveness of the
food-frequency ques tionnaire technique . This review
should be based on the experience of investigators in
both the public and the private sectors. The
Committee anticipates that this review will provide
highly useful information. However, if, after
appropriate investigation, no uses of these data for
important survey purposes can be identified, the
Committee would recommend that the technique then be
deleted from the NHANES. In any event, the Committee
sugges ts that the foot-frequency ques tionnaire
technique not be added to the NFCS be fore the
recommended review is complete.
INFORMATION ON THE COMPOSITION OF FOODS
The survey techniques used collect both qualitative and quantitative data
on food intake. These data are needed to estimate food profiles (and, by der-
ivation, nutrient profiles) of diets, food intake patterns (ant, by deri-
vation, nutrient intake patterns), ant foot relationships (ant, by derivation,
nutrient relationships) to socioeconomic factors. Qualitative and quanti-
tative information is also used to estimate dietary exposure to nonnutritive
food components that have biologic or physiologic importance. Thus, the
qualitative ant quantitative data developed about and from food intake infor-
mation are pivotal for many uses of national survey data on foot consumption
and dietary intake. Some Committee recommendations regarding survey modifi-
catione are directed at this fundamental part of the survey information system
-- its information on the composition of foods.
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EXPANSION OF EXISTING DATA BASES
,
Data on the compos ition of foods have a crucial role in the ef fective use
of survey data on food consumption and dietary intake. A reliable qualitative
and quantitative data base on the composition of foods is fundamental to the
wiser and more effective use of these survey tata.
Much can be done to expand the data on the composition of foods. The Com-
mittee accepts the premise that sufficient knowledge and technology are avail-
able in the field of analytical chemistry to make many needed improvements in
data on the composition of foods at a reasonable cost. In some cases,
existing analytic methods are adequate, ant direct analysis of foods will be
sufficient to acquire the needed data. In other cases, new or improved
methods will be needed. In any event, significant improvements can be made if
improvements are approached sys tematical ly .
The Committee believes that it is realistic to pro ject the success ful
expansion of data bases on the nutrient composition of foods. For example,
although the U. S. food system contains thousands of food items, there are some
general patterns of food consumption. Findings suggest that a "core" of food
items consumed by the population accounts for about 90134 o f the food
consumed. Qualitative and quantitative analys is of core foods in the diet
would provide maximal information with a minimal number of determinations.
The Committee views the continuing expansion of
the data on the composition of foods as an important
contribution to the more effective and wider use of
the results of food consumption and dietary intake
surveys . The Committee, us ing the survey purposes as
guides, recommends that USDA serve as lead agency in
th is ef fort to develop a cos tee f fective approach to
expanding the data base on the composition of foods,
e.g., through the identification and chemical analysis
of core foods in the diet of the U. S. population.
The Committee suggests consideration of the
fol lowing for data acquis i Lion: es tab 1 ish ing or i ter ia
to evaluate the current ~ Late of data on the
composition of foods, using these criteria to evaluate
current methods for food analysis, and , where needed,
developing ~ trategies for improving the data in data
banes on the compos ition of foods .
The Committee also Rugged ts that appropriate
educational strategies on analytic methods be
developed for those who provide analytic data for the
data bases and for those who maintain and evaluate
data base systems. A greater effort should be made to
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educate those who use various data base systems,
including the users of the food consumption and
die tary intake surveys .
DATA ON THE COMPOSITION OF FOODS
A cornerstone of the core purveys is the availability of good qualitative
ant quantitative data on the composition of foods. Such data are used to cal-
culate es timates of dietary exposure to and inges Lion of food components that
have biologic, physiologic, or nutritional significance.
Current data banes on the compos ition of foots are generally des igned to
provide values representative of the "normal" or "usual" amounts of nutrients,
that is, the amounts of nutrients likely to be encountered by the consumer
most of the time. Little data base information is available on the non-
nutritive components of foods. Other analytic data on the composition of
foods often have been limited to the values listed on commercial-product
labels. In the United States, such "label values" reflect both regulatory and
corporate constraints, as well as scientific data on food consumption. More-
over, some values may underestimate or overestimate the nutrient content of
foods, as prepared and consumed. An absolute requirement of any effective use
of survey data on food consumption and dietary intake is a complete data base
on the qualitative and quantitative information about the composition of
foods .
To improve use of future food consumption and
dietary intake surveys, the Committee recommends that
the data bases on the composition of foods be expanded
and improved. Information for data bases on the
composition of foods should be derived from direct
chemical analysis of food products (as prepared and
consumed) wherever analytic methods make such analysis
possible .
The Committee recommends that label values not be
used in data bases on the composition of foods unless
no other information is available. Incorporation of
label value information into future data bases should
be discontinued as information from direct analysis
becomes available.
IMPROVED ANALYTIC METHODS FOR FOOD ANALYSIS
The current knowledge of the nutrient composition of UPS. foods has been
reviewed by Stewart35. Table 6-1 summarizes that review. As indicated in
the table, substantial data on the composition of foods are lacking. The
absence of data may be due to the lack of reliable analytic methods. However,
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this is not always the case; the analytic methods are sometimes considered
reliable. Until foods are analyzed and these data are available, the benefits
of the surveys cannot be realized.
lrhe Committee recommends that, where appropriate
analytic methods exist, analyses be undertaken to
provide missing data on nutrients present in foods,
giving pr iority to foods identified as core foods .
Implementation of this recommendation may require
commitment of resources on the part of USDA and many
other government agencies.
The Committee believes that USDA and agencies
with particular needs for data on the composition of
foots could develop cooperative agreements to ob tain
such data. This would provide useful information both
for a requesting agency and for incorporation into
future data bases on the composition of foods. The
Committee, with the survey purposes as guides,
recommends that USDA serve an lead agency in this
effort .
STANDARDIZED DATA ON COMPOSITION OF FOODS
,
Many uses of food consumption and dietary intake survey data do not
require information on the foods as they are consumed, but involve informs tion
on the foot consumption and dietary intake of components that is derived from
food consumption information. Thus, a necessary step in data processing is
the calculation of the dietary intake of particular food components.
Calculations of dietary exposure to or intake of food components for a
given period involve knowledge of the quantitative consumption of a given
food, qualitative and quantitative information on the composition of the food,
and the Rum of the intakes of individual products containing that component.
Thus, the estimates of food component intake are derived by combining data on
the compos ition of foods with die tary intake data .
The core surveys do not use a common, standardized data base on the compo-
sition of foods to compute the dietary intake of given food components. Each
agency develops its own data on the composition of foods, although some of the
information comes from colon data. Given this, users will continue to have
difficulty in determining whether differences reported in the calculated con-
sumption of food components reflect differences among those surveyed or dif-
ferences in the data bases on the composition of foods that are used to
calculate intake.
Colon, 8 tandardizet data on the compos ition o f foods are required for
effective uses of the survey data and valid comparisons between surveys.
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Differences between surveys in intake estimates that are due to the use of
different data bases on the composition of foods must be precluded.
The Committee strongly recommento that all future
food consumption and dietary intake surveys supported
with federal funds use a common, standardized data
base for estimating dietary intakes of food
components.
The Committee recommento that such a standardized
data base on a given food contain the foot identifier
(i.e., the food code), the mean content ant variance
of the reported components of the food, the number of
samples used to determine the reported measurements,
and an estimate of the reliability of the analytic
data.
For reasons cited earlier having to do with the
purposes of the core surveys, the Committee strongly
recommends that USDA serve as the lead agency in joint
agency efforts to standardize common data on the
composition of foods that are used in federally funded
food consumption and dietary intake surveys. Because
special NHANES needs must be recognized, taken into
account, and met, the Committee recommends that the
NCHS survey planners be directly involved in these
joint agency efforts. The resulting standardized data
bare should be made readily available to the public
and professionals.
COMMON FOOD CODES
Although the codes used are not now standardized between the surveys, the
coding of dietary responses provided by survey subjects is a process common to
the two surveys. In this process, the raw data on each food that is consumed
are evaluated and assigned identification codes. lithe coded food response is
normally among the first data entered into the computerized data collection
syn teme and is necessary to provide an orderly data set . Coding is thus a
crucial step for using food consumption and dietary intake survey data.
The use of a common coding process is crucial for data uses that involve
consumption estimates for the various food components of biologic, physio-
logic, or nutritional importance. Colon food codes can increase the effec-
tiveness of data uses that involve "pooling" information about food con-
sumption and dietary intake, whereas differences in food codes uset by the
core surveys may feat to dif ferences in es timates of tie tary exposure to food
components, depending on the survey data used. Thus, differences in foot
coding between the surveys would affect survey uses, survey users, ant the
usefulness of the purveys.
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Given the importance of foot codes in identifying
foods consumed and in using survey data, the foot
codes used in the surveys should be standardized. The
Committee strongly recommence that future foot
consumption and dietary intake surveys supported by
federal funds use a compatible food coding system for
the identification of foods.
The Committee also recommends that a standard set
of criteria be developed and used for determining how
a food is to be coded when the food (e.g., a
home-recipe food) is not readily identifiable with the
usual nomenclature of commerce. The development of
appropriate foot codes requires consideration of
complex issues beyond the Committee's charge.
However, the Committee recommends that USDA and DHHS
jointly establish a mechanism for the development of
common food codes. The Committee, using the survey
purposes an guides, suggests that USDA serve as the
lead agency in this e f fort . Academic and incus try
scientis ts who use these data should be given an
opportunity to contribute to this development.
POPULATION INFORMAT ION
A fundamental question that the surveys mus t answer is 'who is consuming
the foods" The survey components that address this question must be com-
parable and compatible across the core survey data bases. Application of com-
mon population descriptors clearly will benefit data users.
Although the different purposes and logistics of separate surveys will
inevitably be reflected in the subroutines of the core survey instruments, use
of identical sampling universes and population descriptors would benefit all
data users. The common identifiers that address the question of ''Who is con-
suming the food?" should be retained on the data tapes. Particularly for
application of these data bases to nationwide food and nutrition monitoring,
identical population descriptors across the surveys ensure that information
from individual survey data bases would be consistent.
LINKAGE BETWEEN NFCS AND NHANES
Art important use of the data from the core surveys involves the ability of
users to identify current socioeconomic and foot purchas ing factors associated
with food consumption patterns, dietary intake of food components, and
nutritional status. In addition, these data are used to ascertain the
relation of program or policy changes to desired changes in food consumption
patterns, dietary intake of foot components, and nutritional s tattle. Data
users have expressed a need to facil itate their analyses through linkages
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between the NFCS and the NHANES data bases, because the data on socioeconomic
status ant food purchasing information in the NFCS data banes are more exten-
sive than data in NHANES.
Ideally, linkages between the surveys would be most increased if the
sample subjects in the surveys came from the same households and were, in
fact, the same subjects. In application, however, such sampling would
increase respondents' burden and increase costs, because of the need for
increased sample size.
From the practical standpoint, with other types of improved linkages ,
inferences could be made across the two surveys by using data on the socio-
economic status and foot purchasing determinants of foot consumption from the
NFCS data bases ant then examining characteristic groups in the NHANES for
differences in nutritional and health status.
The Committee has previously discussed the need to have comparable and
compatible food intake methods and standardized data on the composition of
foods to make more effective conjoint use of the separate data bases.
Linkages among foot consumption, dietary intake, and nutritional status data
bases should also include Chose related to the selection and weighting of
survey sub jects and their precise description.
The Committee recommends that survey planners
from USDA ant DHHS continue a joint effort to assese
the current compatibility in the sampl ing frames and
population descriptors of the two surveys. The goal
of this joint effort should be to develop and
implement sampling plans and descriptions of
populations that ensure the greatest possible
compatibility between the two surveys.
When the above compatibility is achieved, it is important for reader e of
repor to to be ab le to 1 ink the f indinge repot ted by the two surveys . Th is
requires identical or at least compatible divisions within variables such as
geographic area, age groups, income levels, and years of education.
The Committee recommends that the joint working
group, mentioned above, set the appropriate divisions
of population descriptors so that they are compatible
between reports from the two surveys.
LINKAGE BEYOND NFCS AND NHANES
There are potential uses that require that information from other sources
be combined with information contained in the two surveys. For example,
certain analyses require linkages of detailed household expenditure survey
data (e .g., that obtained from the Consumer Expenditure Survey ~ and infor-
ma t ion from NFCS .
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a ~
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The Committee recommence that such uses be
identified ant considered and that appropriate linkage
points, where necessary, be established to fulfill
there uses.
There is a specific use that the Committee is already aware of that
requires speci fic linkage information. If adequate identi Eying information is
collected for individuals, it would be possible to link survey data with other
data nets, particularly those involving health outcomes. In particular, the
National Death Index provides a mechanism to follow surveyed individuals for
mortality. To be most effective, Social Security numbers should be collected
in both surveys. Mechanisms to ensure confidentiality are possible. For
example, individual identifying information can be stored with a separate
agency, such as the Bureau of the Census or NCHS, which is covered by specific
privacy acts. Linkage could be accomplished under its auspices without risk
of releas ing individual data.
The Committee recommends that such identi lying
information be collected in both surveys.
GENERAL USER NEEDS
The data userel conferences were designed specifically to develop infor-
mation on and recommendations for modifications in survey methods. However,
the Committee has chosen to include recommendations on some general user needs
that were identifies during its own information gathering process. The recom-
mendations included here are related to data handling techniques and the
implementation of a continuing Late users' information system. The implemen-
tation of these additional but more general recommendations, although not
Specifically a part of the Committees charge, would also serve the needs of
future data users. The Committee therefore urges their consideration.
DETAILED DESCRIPTION OF DATA HANDLING TECHNIQUES
Data users suggested the incorporation of detailed information on data
collection, processing, data reporting, ant other data handling techniques
into the data tapes. Such descriptions would serve user needs for more
detailed description about the data handling (data documentation).
Some user needs relate to quantitative documentation of response rates and
of standardization proceedures. Other specific user needs for data documen-
tation that were identi f fed are factors involved in decis ions about data
process ing, reporting, and rules and procedures for survey design and data
processing (e.g., sample weighting, coding rules, and rules for imputed or
estimated values). In addition, some data users suggested the incorporation
of documentation about data developed from such procedures (e.g., distinctions
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between absence of values and "zero" values that are as appropriate as any
other values, estimates of measurement, precision and reliability36~.
Some Committee recommendations in Chapter 6 are related to the standard-
ization of methods and information. Were such recommendations are imple-
mented, the Committee anticipates that there will also be standardization of
data handing techniques.
The Committee recommend. that, where fees ib le.
information on the group of techniques necessary be
incorporated into the data tapes and be added to
published data reports to ensure a complete record of
the reasons for changes in variables.
Incorporation of data documentation would assist users, particularly users
of data tapes, in undertaking more effective and appropriate data analyses.
The Committee anticipates that some aspects of Rate documentation will be
peculiar to the separate core survey data bases and will be incorporated into
only one agency 'a data base tapes.
Where methods are standardized in and common to
the two core surveys, the Committee recommends that
each agency ts data base tapes contain identical data
documentation.
IMPLEMENTATION OF A POSTRELEASE INFORMATION SYSTEM
AS illu8 bated in Chapters 2, 3, 4, and 5, uses for data on the food con-
sumption and dietary intake of the U.S. population are many and varied. There
are only a few current efforts to ensure that postrelease information about
the data is itself provided deco data users in a timely ant systematic way. For
example, an NHANES users group meets informally three times a year. The users
group address list provides a means of conveying important postrelease infor-
mation about the NHANES data, but only to those on the list .
USDA's Human Nutrition Information Service ha. address lists for those who
have asked for data or particular pub fished reports . The National Technical
Information Service maintains a list of those who have ordered the data tapes.
However, those lists often do not provide the names of the data users, but
only institutions ' mail-receiving addresses .
The Committee suggests that means of providing
continuing postreleane information to data users be
explored and that a system be developed and
implemented to provide this information to data
users . The fees ib ility of us ing modern bib liograph ic
information systems, an information feedback system,
ant an educational sys tem for data users should all be
reviewed .
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The Committee suggests that the agencies review
the use by scientific journals and literature search
systems of a keyword notation system when publications
cite or use NFCS ant NHANES survey data. The goal of
this effort would be assurance that, when these data
are cites or us et in scientific reports, the specific
articles can be identifies and retrieved through the
modern computer izet ~ cienti f ic 1 iterature s earch
systems (e.g., Medline, Toxline, Biological Abstracts,
and Chemical Abe tracts ~ .
The Committee further suggests the development
and implementation of an information feedback sys tem
between data collectors and data users. Both groups
would then be able to develop an effective knowledge
of data uses, data users' concerns, and other
information that can help to ensure both the
appropriate use of data and meeting the needs of
future data users.
In addition, the Committee urges consideration of
a continuing educational system, perhaps through the
development of short courses for data users, to
provide useful information to the broad community of
users. An educational system can help to prevent
unrealis tic or inappropriate interpretations o f and
expectations for these data. In the view of the
Committee, the variety of uses for these data makes it
likely that an interagency effort in user education
would be most useful and most cost~ffective.
SUMMARY
lathe foregoing recononendatione of. the Committee are related primarily to
modifications in survey design, data processing, and reporting that respond to
expressed user needs for data that are timely and that are comparable ant com-
patible across the separate NFCS and NHA~S data bases. Others concern modi-
fications in food intake methods and use of intake methods common to the
separate surveys. The Committee also recommence expans ion of the Individual
Dietary Intake component of the NFCS and the NHANES to incorporate continuous
data collection and processing and reporting of accumulated data over a 5-year
period (a 5-year moving average) while the Household Food Use component of the
NFCS is continued on an intermittent basis.
Committee recommendations related to food intake information are des igned
to respond to users' needs for better and more compatible qualitative and
quantitative information on the foods that are consumed. The Committee recom-
mendations include expansion and standardization of current data bases on the
compos ition of foods and standardization of food coding.
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Further recommendatione focus on user needs for more comparable and com-
patible information about the subjects in the separate survey samples. Some
general recommendatione are also included in the Committee's recommendations.
Although not specifically within the Committee's charge, the general reco~en-
dations are designed to respond to needs of both current and future data users
for more detailed use of survey tats.
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Table 6-1. Foot composition knowledge as percent
of applicable food categories
containing substantial datea
Nutr lent
To tat protein
Total fat
Niac in
Riboflavin (vitamin B2
Th iamin (vitamin B
Calcium
Iron
Phos phones
Sodium
Pa tas ~ ium
Chol es tero 1
Magnet ium
Zinc
Copper
Fatty acids
Vi tamin A
Vi tamin B6
Simple sugars
Percent of food categories
with subs tantial data
~! . _
82
54
53
53
53
46
44
44
44
44
42
40
40
37
34
27
20
10
a USDA has divided food supply into 42 broad categories. Because come
nutrients are known to be absent from some foods and foot categories, not all
nutrient analyses are desired or needed for all 42 categories. Percent of
food categories with substantial data is calculated only for categories in
which nutrient is suspected to be present in important amount. "Substantial
data" means sufficient information to establish normal amount of nutrient in
most foots in category. Calculated from Stewart.36
Representative terms from entire chapter:
food consumption
