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OVERVIEW AND SUMMARY RECOMMENDATIONS In response to a request from the Human Nutrition Information Service of the U.S. Department of Agriculture (USDA), a Coordinating Committee on Evalu- ation of Food Consumption Surveys was es tablished under the auspices of the Food and Nutrition Board (FNB) in the National Research Council's Commission on Life Sciences to review ways in which data from the Nationwide Food Con- sumption Survey (NFCS) are used and to make recommendations on survey design that would facilitate wider application of survey data. Within the framework of the original request, the Committee incorporated into its study-a review of and recommendations for the dietary component of the National Health and Nutrition Examination Survey (NHANES), a project of the National Center for Health Statistics of the Department of Health and Human Services (DHHS). After developing and conducting a workshop and symposium, whose participants were interested current and potential users of the survey data, the Committee evaluated the information obtained therefrom and identified specific user needs. This report, to those responsible for the surveys, contains the Com- mittee's findings and recommendations. SURVEYS: BACKGROUND - The 1977-1978 NFCS sample was approximately 15,000 households and more than 30,000 individuals. Information was obtained on the kind, quantity, and monetary value of foods consumed by the U.S. population and representative groups and on various household characteristics. The NFCS provides data needed to estimate the amounts and variability of food and nutrients in U.S. household and individual diets and to estimate dietary adequacy. Repeated surveys provide data that permit estimates of changes in the amounts of food and nutrients in U.S. diets and measurement of trends in dietary adequacy. In contrast, the 1976-1980 NHANES, a survey of clinical and nutritional condition involving more than 20,000 individuals, provided data needed to estimate the prevalence of physical states or disease conditions in the U.S. population -- e.g., normative or descriptive data -- and biochemical data that serve as descriptors of biochemical, nutritional, and, perhaps indirectly, physiologic status. Successive surveys permit the repeated measurements needed to monitor changes in health and in the biochemical aspects of nutritional status over time. IDENTIFICATION OF CURRENT AND POTENTIAL USES AND USER NEEDS . A major finding resulting from the workshop and symposium efforts was identification of a wide variety of uses for the survey data. Clearly, the NFCS data are used for foodand nutrition-related issues and the NHANES data are used for nutritionand health-related issues. However, the uses for
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— 4 — these data go far beyond traditional food and nutrition questions. For example, the survey data are used in assessing questions related to agri- cultural production of food and economic demand analyses, as well as for socioeconomic analyses of food consumption and the factors that affect it. Questions related to food safety and food-related toxicology are also addressed with these data, as are assessments of the design and marketing of food products. Specific examples of uses are found in Chapters 2 and 3. In some instances, one particular data base is used. In other instances, data users want to use more than one data base, e.g., by using the data bases conjointly. Where information from more than one data base is used, greater comparability and compatibility of the survey data bases are needed. The ability to put information from one data base together with that from another and thus link the data was regarded as necessary for wider and more effective use of the data. Data users did not look on the present limited overlap in data between surveys as redundant or unnecessary, but rather as contributing an important set of data points providing an opportunity for data linkage between survey data bases. Linkage to nondietary data bases also can be Important ~ for example ~ when they are linked both to data on health and disease and to data on demographic and socioeconomic characteristics of sur- veyed populations. For this reason, the Committee chose to include a per- spective on con joint uses of the data in its discussions (Chapter 5 ~ . Timely data release and reporting were commonly identified needs. Data users also wanted the surveys to provide even more data than they do now and even more specific data than are now provided on public data tapes. Users recommended that the survey data bases provide highly detailed information not only about foods themselves , but also about their nutrients, added substances, and con taminants . COMMITTEE PERSPECTI~F. nN nATA TT~F~ Vera prom One surveys provide answers to some basic questions that cross the scientific disciplines and interests of all data users. For example, detailed and specific identification of who in the population consumes what ~ _ foods is needed not only for assessing determinants that affect food and nutritional status, but also for designing, analyzing, or modifying a variety of food-related assistance, education, and regulatory programs. A nationwide food and nutrition monitoring system must be viewed both in the light of its own purposes and as a synthesis of the purposes of the surveys that would contribute data to the monitoring system. Clearly, the data bases contributing to the monitoring system should meet its needs. Equally important, however, the data collection and reporting methods of the separate data bases must also meet the existing and future needs of data users, for example, the independent uses of the NFCS and NHANES data bases that would form the core of a food and nutrition monitoring system.-
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1 — 5 — It is the conjoint use of data from the separate core surveys that pro- vides information of the scope needed to describe food consumption, nutrient intake, and nutritional status. Conjoint use of these core survey data bases helps to identify food-, diet-, or nutrient-related public health concerns, from inadequate intake to excess consumption, as well as to identify trends in those concerns. Given the scope of the public concerns to be addressed through nationwide food and nutrition monitoring, neither the NFCS nor the NHANES alone can provide the needed information; data from both surveys will be needed. Because these surveys have different purposes, they cannot be merged into a single survey without the risk of compromising some of their separate fun- damental purposes. Moreover, it is unlikely that a single survey can be designed to satisfy all the needs and fit all the uses for survey data on food consumpt ion and d ietary intake . A national data collection system (involving data from both the NFCS and the NHANES, as well as other data) would provide information needed to assess the foodand nutrition-related risks to health that may be amenable to inter- vention. An improved data collection system is needed to ensure the effective conjoint use of the separate survey data bases needed for a system of nation- wide food and nutrition monitoring. However, it is equally important to bear in mind that each of the separate core surveys has uses that are independent of its contribution of data for nationwide food and nutrition monitoring. Thus, the basis for the Committee's assessment of the uses for existing survey data was the identification of data uses and needs common to the separate core surveys and to nationwide food and nutrition monitoring. The design and data reporting implications that evolve from these common data uses and needs are the basis for the recommendations in this report. Essential survey purposes and uses for the data from the separate core surveys should not be compromised by survey modifications intended solely to foster increased nationwide food and nutrition monitoring capabilities. The Committeets task was to select, from among the many suggestions for possible modifications offered by data users, suggestions that did not imply such compromise. SUMMARY RECOMMENDATIONS . The Committeets recommendations have implications for survey design, data reporting, and data use alone or in combination. Where conjoint use of data from different surveys is involved, as it would be in a nationwide food and nutrition monitoring system, recommendations applicable to one survey could have implications for a different survey data base. The rationale and recom- mendations of the Committee are discussed in detail in Chapters 6 and 7. In this summary, the recommendations alone are presented and are grouped under general headings.
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— 6 — Detailed and specific information on who is consuming what is needed for all data used Recommendations for modifications of survey methods that improve the utility of data developed from answering these common questions are of high priority to all data users. Most of the Committee's recom- mendations are therefore designed to serve these common data user needs. Other recommendations respond to more general needs involving the data themselves. RECOMMENDAT IONS FOR SURVEY DES ION AND INTAKE METHODS . The surveys should be continuously evaluated. The Committee has suggested a list of questions which should be addressed for each priority use to assure that the surveys provide the prerequis ite specificity and reliability of in forma t ion for that use . The NFCS Individual Dietary Intake component and the NHANES should be redes igned as continuous surveys with data collection from the total sample distributed over a number of years. Data accumulated in preceding years, when added to the data collected during a given year ~ would provide data on the total sample. Continuous data collecting, processing, and reporting systems should be implemented. The Household Food Use component of the NFCS should continue on a regular, intermittent basis unless future study demonstrates that some other design (e.g., continuous) is more advantageous. USDA should continue to collect replicated data on food consumption and dietary intake of individuals. Because of the need for statistical infor- mation on intraindividual variability, resources should be committed to maintaining, at a minimum, collection of 3 data-days of individual intake from a representative sample of the U.S. population. Survey planners for the NHANES should consider the addition of replicated data. Methods for the 24-hour recall of food consumption in the two surveys should be made more uniform between the surveys, including standardization of interviewing techniques and the format of soliciting information from sub- jects. The use of the food-frequency questionnaire technique should undergo further study before decisions are made about its addition to the NFCS. RECOMMENDATIONS FOR POPULATION DESCRIPTORS _ A joint working group composed of survey planners from both the NFCS and the NHANES should assess the sampling needs of the surveys and develop plans to foster sampling compatibility. Population descriptors used by the surveys should also be identical. The Committee recommends that the detailed popu- lation and socioeconomic descriptors of households now collected in the NFCS household surveys be incorporated in the Committee's proposed continuous NFCS s urvey o f ind iv idua 1 d ie t ary in take .
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— 7 — RECOMMENDATIONS FOR FOOD AND NUTRIENT DESCRIPTORS . . Each of the food consumption and dietary intake surveys should add core questions to obtain qualitative and quantitative information on the use of dietary (e.g., vitamin-mineral) supplements, medications, alcoholic beverages, and other discretionary dietary components (e.g., sugar, salt, ant fat). The surveys should also incorporate core questions on impediments to food intake. All future food consumption and dietary intake surveys supported by federal funds should use standardized data on the composition of foods and compatible food codes to identify identical foods. Identical criteria should be used to determine how foods are coded when they are not readily identi- fiable by the usual nomenclature of commerce. The use of universal product codes (UPCs) should be considered in the development of standardized food codes. A cost-effective approach should be used to expand the data base on the composition of foods through the identification and direct chemical analysis of core foods in the diet of the U.S. population. Analyses should be under- taken to provide missing data on the composition of foods, particularly for the nutrients in foods. Large-scale collection of product brand-name information should be deferred, until the utility of UPC s or other systems for reliable and valid large-scale collection of such data can be reviewed. Joint, interagency efforts should be undertaken to expand and improve qualitative and quantitative data on the composition of foods. A priority goal of federally supported research should be an improvement in analytic methods needed to develop data on the composition of foods. Appropriate and validated analytic methods should be used for determining the composition of foods, particularly the components whose dietary intake in the United States, whether high or low, is of public-health importance or scientific concern. Over the longer term, an expanded data base on the composition of foods should include standardized data on nonnutritive food components, food ingre- dients, and unintentional components of foods. GENERAL RECOMMENDATIONS Information on the details of data handling (data documentation) should be incorporated into the data tapes and added to published data reports. A wider effort should be made to educate developers and users of various data bases about analytic methods and data interpretation (e.g., users of the food con- sumption and dietary intake survey data).
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— 8 - . Because of the need for the data tapes over time, data tape 8 forage and maintenance methods should be reviewed. Interagency efforts should be undertaken to develop a system to provide continuing information to data users, including information on the use of modern bibliographic systems, development of feedback systems for data users and collectors, and an educational system for data users. CONTINUING EVALUATIVE PROCESSES The Committee has suggested, in Appendix A, a process for assessing implications of future design modifications of the NFCS and the NHANES. The suggested process provides the agencies with a starting point for developing modifications in survey design and data reporting that respond to evolving user needs for data.
Representative terms from entire chapter: