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3 THE NAT IONAL HEALTH AND NUTRIT ION EXAMINAT ION SURVEY Background information presented in this chapter was provided directly to the Committee and that presented by U. S. Department of Health and Human Services National Health and Nutrition Examination Survey specialists at a Committee-sponsored June 1983 workshop and October 1983 Symposium. This information is presented without Committee comment, assessment, or evaluation. HISTORY _ The National Health Survey Act of 1956 authorized the secretary of the Department of Health, Education, and Welfare (now the Department of Health and Human Services), acting through the National Center for Health Statistics (NCHS), to collect statistics on a wide range of health issues. Given this directive, NCHS has conducted health examination surveys for more than 20 years. Among other topics, NCHS collects statistics on determinants of health and on the extent and nature of illness or disability of the U.S. population. In 1960-1962, the first National Health Examination Survey was con- ducted. The sample population for this survey was adults 18-74 years old. Two additional surveys were conducted during the 1960s on children 6-11 years old and adolescents 12-17 years old, respectively. In 1971, the range of topics included in the survey was extended to include nutritional status. Indexes of nutritional status were to be obtained through a medical history, a dietary interview, a physician's examination, medical procedures and biochemical tests, and body measurements. This survey, the first National Health and Nutrition Examination Survey (NHANES I), was conducted between 1971 and 1974. NHANES II, conducted between 1976 and 1980, extended the age range to include infants 6 months to 1 year old. Currently, the NCHS is conducting the Hispanic Health and Nutrition Examination Survey (HHANES, 1982-1984) of persons of Mexican-American, Puerto Rican, and Cuban ancestry residing in the southwestern U.S., the New York City area, and Dade County, Florida. The next national survey, NHANES III, is scheduled to begin in 1987. PURPOSES The fundamental purposes of the NHANES are "to develop information on the total prevalence of a disease condition or a physical state; to provide descriptive or normative information; and to provide information on the
32 interrelationships of health and nutrition variables within the population groups" (R. SO Murphy, Director, Health Statistics Branch, National Center for Health Statistics, DHHS, personal communication). Additional purposes of the NHANES are "to measure the health and nutritional status of the U.S. popu- lation and specific subgroups and to monitor changes in health and nutritional status over time."4 Thus, the surveys have provided estimates of the prevalence of charac- teristics or conditions in the American population, and normative or descrip- tive data have been developed, such as data on weight and stature. Through successive surveys, repeated collection of these estimates permits the assess- ment of changes in health and nutritional status over time. DESIGN GENERAL FEATURES One of the purposes of the NHANES II program with respect to nutritional status assessment required that the program continue to use, with some modifi- cations, the same format as NHANES I. To monitor nutritional status, the data collected needed not only to be comparable (at least largely), but also, as in NHANES I, to be collected on a probability sample of the noninstitutionalized civilian population of the United States. The general structure of the NHANES II sample design was therefore similar to that of NHANES I. The design was that of a stratified, multistage, probability cluster sample of households throughout the United States. The sample selection process involved a number of factors, including the selection of primary sampling units, household clusters, and households. A primary sampl ing unit (PSU) was a primary location, generally a county or small group of contiguous counties, from which sample housing units and sample persons were selected.9 When the definition and stratification procedures were completed, 64 PSUs throughout the United States were included in the NHANES II survey plan. The cl inical examinations and other procedures were conducted in specially designed mobile examination centers. These mobile centers were moved from location to location in a predetermined fashion to achieve economy of operation and to avoid the North in the winter. At any time during the survey period, two mobile examination centers were operating (in different locations ~ while a third was being relocated. These mobile centers provided a controlled, standardized environment for the clinical examinations and tests. Thus, the clinical procedures could be conducted by a trained staff that moved from site to site with the mobile centers. Because of the small number of mobile centers, the logistic constraints involved in moving and setting up the centers, the large number of subjects, and the length of each examination, the total period for data collection was 4 years. The average length of an examination was 2-3 hours, but examinations
1 33 varied, depending on the age of the subject. For example, the examination of a preschool child lasted no more than 2 hours, and that for an adult no more than 3 hour s . STATISTICAL DES ION The survey was designed to produce statistics for four broad geographic regions of the United States and for the total population by sex, age, race, and income classification. NHANES II was a probability sample of the civilian, noninstitutionalized population of the United States aged 6 months through 74 years. For nutritional assessment, three population groups of presumed higher risk of malnutrition were of special sampling interest. These groups were preschool children (6 months to 5 years old), the aged (60-74 years old) , and the poor (persons below the poverty levels defined by the U. S. Bureau of the Census). These three groups were oversampled to improve the reliability of the statistics generated about them. Although women of child-bearing age were also considered to be at risk of malnutrition, oversampling of them was not necessary, because adequate numbers were included in the sample. A total of 21,000 examined persons was desired as the sample size. The number selected from each of the 64 PSUs was to be between 300 and 600. In an initial interview conducted in the household, sociodemographic information and medical histories were collected. A visit to a mobile exami- nation center was then scheduled for each subject. At the mobile center, the physical examination, dietary interview, anthropometry, and other procedures and tes ts were conducted. In the end, 27, 801 persons were interviewed and 20, 322 persons were examined in the 1976-1980 NHANES (NHANES lI). Because not all interviewed persons were examined, appropriate statistical adjustments for nonresponse were made. These adjustments brought the sum of the final sample weights into close alignment with the sex, age, and race estimates of the Bureau of the Census at the midpoint of NHANES Il. DATA COLLECTION METHODS The five ma jar components of NHANES II were a household questionnaire, a -medical-history questionnaire, dietary questionnaires, a physical examination by a physician, and special clinical procedures and tests, including x rays and tests on samples of blood and urine . The household questionnaire asked for information on family relation- ship; some demographic items, such as sex, age, and race of family members; housing; occupation, income, and educational level of each family member; and participation in the food stamp program and the school breakfast and lunch program. Two medical-history questionnaires were used; one questionnaire was
t 34 used for children 6 months to 11 years old, and a different one for persons 12-74 years old. Both household and medical-hi~tory interviews were conducted in the respondent's home. The dietary interview, physical examination, and special clinical pro- cedures and tests (depending on the age of the subject) were conducted when the subject arrived at the mobile examination center. The procedures and tests included body measurements (all subjects); skin-prick tests for allergy (persons 6-74 years old); x rays of cervical spine, lumbar spine (except for women under 50), and chest (persons 25-74 years old except for pregnant women) ; urine (persons 6-74 years old); and blood (all subjects). A number of nutrition-related assays were performed on blood samples. These included assays for serum albumin, serum vitamins A and C, serum lipids (cholesterol, triglycerides, and high-density lipoproteins), protoporphyrin, serum iron, total iron binding capacity, serum zinc, and serum copper. Blood samples that yielded abnormal readings for complete blood count, hemoglobin, hematocrit, or mean corpuscular volume were tested further for red-cell folate, serum folate, serum ferritin, and serum vitamin B12 to be compared with an equal number of blood samples with normal hematologic values. DIE TARY COMPONENT The dietary component of the survey consisted of a recall of dietary intake for the preceding 24 hours, usual food consumption for the preceding three months, and questions about the use of diets, particular medications, and vitamin and mineral supplements. In the 24-hour dietary recall procedure, respondents were asked to report all foods and beverages consumed and estimate portion sizes by using food models as guides. In addition to asking about foods and portion sizes, interviewers asked about the time of day that a food was eaten and about its source. The time of day was coded in military hours. The in question period was indicated as (1) a.m., (2) noon, (3) between meals, (4) p.m., or (5) total day. The source of a food was coded as home, school, restaurant, or other. The interviewer coded each 24-hour recal 1 within 72 hours of the inter- view. The food code book developed for the survey contained five-digit codes for approximately 4,762 food items. Where an appropriate code was lacking, the nutritionist at NHANES headquarters assigned needed code numbers. Each food item was identified by name (including brand names, if appropriate); whether it was raw, dry, or frozen; how it was prepared; and, for mixed dishes without food codes, its ma jar ingredients. For example, in the NHANES II data base tape (called ache model-gram tape), chicken fricassee would be coded as 15 00749: 15 -- mixed protein dishes. 00749 -- chicken fricassee, home recipe.
35 In published data, however, food codes were not used. Rather, the data were presented as nutrients obtained from identifiable food-group clusters, e.g., prose in from mixed-prose in dishes . For NHANES II, a data base on the compos ition of foods based on and updated from NHANES I was used to calculate the macronutrient, fat, vitamin, and mineral content of the foods reported as consumed. Modifications of the NHANES I data base included revised UBDA data and industrial data on the com- position of both new food products and brand-name products of unique formu- lation. 10 The NHANES II data base on the composition of foods was developed for use in the NHANES survey and differed in some respects from other data bases on the composition of foods (e.g., the USDA's data bases). A food-frequency interview was used to obtain information on the con- sumption, during the previous 3 months, of foods in 18 groups. Frequency was coded in whole numbers, and indicated whether foods were never eaten, eaten less than once a week, or unknown. Unknown was coded when the respondent ate the food but could not indicate frequency. The interval at which the food was usually eaten was coded as never, daily, weekly, or less than once weekly. The respondent was asked about the use and type of vitamin and mineral supplements. Type and frequency of alchohol consumption and use of the salt shaker at the table were included in the food-frequency questionnaire. Use of tab le Sal t was coded as rarely or never, occas tonal ly or seldom, and fre- quently or always. The dietary supplement ques tionnaire contained ques Lions about whether the respondent was on a special diet and, if so, what type and for how long. One question dealt with the previous week' s use of nine categories of commonly prescribed medications that had been identified as possibly affecting test results or their interpretation. Another question was related to prob lems preventing the respondent from obtaining needed groceries. The final question was about trouble in swallowing, pain, nausea and vomiting after eating, and loss of appetite. A questionnaire on medication, vitamin, and mineral use was administered in the home. Respondents were asked specific information on brand names and manufacturers' names of medications and vitamin and mineral preparations they used. Reasons for using vitamin or mineral supplements and medications were also requested. QUALITY ASSURANCE - The quality of the dietary component of the survey was monitored at several levels. All interviews were conducted by dietary interviewers who had at least a bachelor's degree in home economics. Before the survey began, the interviewers were trained both in interview techniques and in coding of the food items identified in the 24-hour dietary recall. A manual issued to each interviewer described the procedures to be followed.ll
36 To promote consistency in quality control, dietary interviewers period- ically reviewed and evaluated each other's work. At every location, each interviewer tape-recorded two randomly selected subject interviews. These recordings were then evaluated at headquarters for adherence to procedures. Randomly selected 24-hour recall forms were manually reviewed at head- quarters before programmatic edits were completed. To detect errors and unusual resul ts from a particular location or from a particular dietary inter- viewer, the NHANES headquarters staff reviewed the "ranges" of nutrient intake for each res pondent . DATA PROCESSING Preparation of data and reports of the NHANES II findings involved several steps. With some items, such as x-ray pictures, interpretations were required to produce data units that could then be coded. Coded data were key punched into machine-readable form. The data were edited and validated. Sampling weights -- the designated number of people in the population repre- sented by a survey subject -- were determined. For selected measures, impu- tation procedures for item nonresponse were developed and reviewed. Data were then analyzed and reports were developed. DATA REPORTING Descriptive, analytic, and methodologic reports were published in Vital and Health Statistics (Series 1, 2, and 11), a publication of the NCHS. All ~ . completely edited, validated, and documented tapes were released for public use through the National Technical Information Service. Information has also been made available in journal articles and in presentations at professional meetings. RESEARCH IN IT IAT IVE S NCHS research is of two kinds: statistical analyses describing the potential contribution of demographic, biologic, ant other variables to deter- minants of health and nutritional status; and development, testing, and transfer of methods involved in conducting surveys and validating data from them. This research is conducted intramurally (that is , within DHHS), often in conjunction with the Food and Drug Administration (FDA), Centers for Disease Control (CDC), or the National Institutes of Health (NIH). No extra- mural research, as with a grants program, is supported directly by NCHS. Although research in support of the surveys is needed, little funding is available .
t ~ 37 - The current aged planned nutritional or nutrition-related research activ- ities involving data from the NHANES include statistical analyses, research on survey methods, and identification of research needs in applied nutrition. For example, working with FDA and the National Heart, Lung, and Blood Institute of NIH, NCHS plans to analyze statistical relationships among cardiovascular-disease risk factors and nutritional variables from NHANES data. Analyses will include physical, physiologic, and biochemical measure- ments; electrocardiogram interpretations; x-ray results; and medical histories. The resulting data will be analyzed to determine the prevalence and severity of various heart conditions. The relationships of specific heart-disease morbidity to such risk factors as blood pressure, serum choles- terol concentration, body-mass index, smoking habits, drinking habits, blood lead concentration, and dietary habits will also be examined. These results and other analyses will permit DHHS to measure its degree of success in meeting its nutrition objectivesl2. The results of the analyses are impor- tant both for establishing baseline information for health promotion and disease prevention objectives and for identifying and assessing population groups at highest risk of morbidity and mortality. Using the NHANES data on nutrition monitoring and surveillance, NCHS is collaborating with FDA to determine the prevalence of osteoporosis and to identify specific population groups at risk. This information is important because of the relative increase in the number of older persons (who are most prone to osteoporosis) in the population, the consequences of the disease, and the costs of its medical care. NHANES data on the ratio of subjects' bone density to cortical thickness, their medical history, and related items will be used to identify persons with osteoporosis. The analyses may also include examination of the relationships between osteoporosis and periodontal disease. Results of these analyses will help to form the basis for FDA recommendations regarding calcium fortification of the food supply and nutrition education efforts for such groups. NHANES data related to iron, zinc, folacin, and vitamin A are being analyzed in another collaborative project with FDA. The purpose of the pro- ject is to determine the prevalence both of nutrient-deficiency states and of nutrient-excess states, as well as to identify population groups that may be at high risk of experiencing nutrient-related problems. The goal is to assess the nutritional status of the population and to develop a national food- fortification policy that considers the interrelationships among nutrients. Two aspects of survey methodology currently being studied are the accuracy of respondent-reported height and weight and the development and validation of a quantified food-frequency questionnaire to permit estimation of intakes for 1-, 7-, and 30-day periods. Data from two previously conducted surveys will be used to validate the food-frequency questionnaire developed for a followup study of NHANES I. Such information will be useful in future NHANES and special surveys for relating usual food and nutrient intake to health variables.
- 38 - Research on telephone survey methods (including questionnaires, sampling frames, ant recoding procedures) and data reduction has been pursued in the NCHS nutrition-related projects. Other study projects have included health and nutrition-related habits, e.g., smoking and the use of alcoholic beverages. Potential bias in respondents and nonrespondents has been evaluated. RESEARCH NEEDS . Appl fed research in connection with the NHANES wit 1 require greater financial and other support than is now available. Gaps in nutrition knowl- edge may be filled, only in part, through the analysis of NCHS survey data and method transfer. To improve the interpretation of NCHS survey data, research is needed on: the functional consequences of malnutrition and minimal requirements for nutrients; behavioral, cultural, and genetic determinants of group differences in nutrition status; the health implications of very-low- calorie and extremely-low-calorie diets; nutrient toxicity; early nutrition- related indicators of degenerative diseases; pathophysiologic consequences of nonnutritive substances; biologic significance of trace minerals; relation- ships between nutrition and immune system response; relationships between nutrition and physical and cognitive performance; and relationships between maternal nutritional status and birth outcome. The dietary data component of the NHANES may be of use in studies of bioavailability and safety, identification of new foods that require new analytic techniques to assess their nutrient value, the health ramifications of foods and "alternative diets," and in the development of standards for analyzing and interpreting survey data that are sensitive to physical, physio- logic, and ethnic characteristics. The reliability of NHANES estimates of prevalence of deficient or poten- tially toxic intake of nutrients would be improved by the availablility of better standard references and their consistent use by analytic laboratories. Research is also needed to develop highly sensitive methods for detecting initial states of nutrient depletion and of toxicity. Such methods, for incorporation in surveys, need to be automated, rapid, inexpensive, and . ~ ~ ~ mln~ma. .. .y 1nvas eve. The nutrients with the highest priority for method development are those whose intake is known to be low or high and for which there is evidence of harm or benefit to the public. NHANES survey data and data from the U.S. Department of Agriculture (USDA) Nationwide Food Consumption Surveys (NFCS) indicate that intake of vitamin B6, iron, calcium, and magnesium is low with respect to the Recommended Dietary Allowances. Methodologic development and validation are needed to assess the health effects of low intake of these and other nutrients, including the nutritionally essential trace minerals.
- 39 - New survey needs become apparent as new nutrition and diet concerns arise. There is great need for epidemiologic surveys to collect data on nutrition-related issues · Such surveys might include, for example, comparison of nutritional status as determined by surveillance data with that measured in a representative sample of the target population. FUTURE PLANS NHANES III is scheduled to begin in 1987. As the content of the survey is be ing developed, items that should be considered as core components of the survey will be discussed. Such core components would be conducted with all subjects and would be repeated in future surveys. Other (noncore) components would be administered only to a subsample of subjects. In preparing for NHANES III, survey planners will solicit suggestions from federal agencies, the Congress, the public-health and nutrition com- munities, researchers, foundations, and associations. A variety of mechanisms are being considered to gather recommendations from these groups, including letters, meetings, and notices in journals. Concurrently with decisions about survey content, preliminary decisions will be made about sample design, data processing, coordination with other surveys, addition of a longitudinal component, and continuous monitoring of high-risk groups. Some of the issues to be settled are whether it is feasible to include, as primary sampling units in NHANES III, the primary sampling units in the DHHS Health Interview Survey or the NFCS; how automation in data processing can improve speed, cut costs, and decrease errors; and whether NHANES III can use the same data base on the composition of foods as is used in NFCS. It is conceivable that the dietary interview will be automated in NHANES III. Coding and edit checks could then be accomplished during entry of data and while the interview is being conducted. Changes could also be made in the current format , for example ? increas ing the number of times that a 24-hour recall of dietary intake is obtained from a sample person. Detailed planning about methods and design will begin in 1984-1985. Having defined the survey content, planners will decide which methods are most appropriate. Pilot tests will be conducted with preliminary questionnaires and protocols. During 1985-1986, the results of the pilot tests will be analyzed and protocols, procedures, and questionnaires Will be revised appropriately. Final Office of Management and Budget clearance is necessary before NHANES III can begin.
- - 40 - USES OF DTETARY DATA FROM NHANES SURVEYS NHANES dietary data have four main uses. Two of them are unique to NHANES: relation of food consumption patterns and nutrient intake of sub- populations of the United States to physical and physiologic indicators of health status and examination of interactions of nutrition-related variables -- such as dietary intake, physical measurements, and biochemical assessments -- with health conditions determined through health histories and physician examinations. The other main uses are the determination of food consumption patterns and nutrient intake of subpopulations of the United States by such characteristics as age, race, sex, and education and the development and evaluation of other surveys or studies through use of NHANES survey methods and data. Uses of NHANES dietary data can be categorized according to their pur- poses of use, e.g., to formulate or change programs or policies, to increase basic knowledge through research, and to develop educational material and transfer information. Users of the data are in a variety of public and private sectors, including federal and state governments, food manufacturers, researchers, educators, and students. The examples listed here were provided by DHHS/NHANES staff and were selected to represent the various kinds of uses and users of NHANES dietary data. DETERMINATION OF FOOD CONSUMPTION PATTERNS AND NUTRIENT INTAKE OF . SUBPOPULATIONS OF THE UNITED STATES The National Cancer Institute has used 24-hour recall and food-frequency data to assess, for policy purposes, the current American diet, with a focus on foods that are harmful or protective relative to the development of cancer. A drug manufacturing firm has used vitamin-mineral supplement data and 24-hour recall data to aid in evaluating whether segments of the population are vitamin-deficient. The Canadian government has used the dietary data to assess the nutritional adequacy of the food supply, with a focus on food fortification programs, guide lines, and label ing . A marketing consulting firm has used the dietary data to examine the frequency of consumption of low-calorie custards, water-packed fruits, and other "ties foods . " A university research division has used NHANES demographic and dietary data to study the nutritional status of the elderly and characteristics of food-stamp users.
b 41 A university has used 24-hour recall data to assess the variability in food consumption of~adult~ and to assess nutrient-intake diversity. A medical society has used 24-hour recall data to assess calcium and phosphorus intake in the United States. A univers ity has used analyses of NHANES dietary data to s tudy the relationship of several sociologic variables and obesity. A drug manufacturing company has used the dietary data to maintain and improve its data base for a nutrition education program. A western university has used food consumption pattern data in its research on living arrangements and dietary patterns of the elderly. An information service has used dietary data to disseminate information on nutrient and food consumption habits of children and the elderly to clients. An eastern state has used 24-hour recall data on children in a publication on the "state of the child." The Food and Drug Administration has used NHANES data on breastfeeding as part of a study on attitudes toward, practices in, and knowledge about food and nutrition. A public-relations firm has used vitamin-mineral intake data and food-item consumption data to disseminate information to clients. A university has used 24-hour recall data to develop a regional food consumpt ion pro f ile . An equipment manufacturer has used 24-hour recall data -- especially food sources of vitamin A, calcium, phophorus, and riboflavin -- relative to a concern about loss of nutritive value in packaged milk. A milk trade association has used NHANES dietary data to determine the milk consumption pattern of young adults. RELATION OF FOOD CONSUMPTION PATTERNS AND NUTRIENT INTAKE OF SUBPOPULATIONS OF . . . . . THE-UNITED STATES TO PHYSICAL AND PHYSIOLOGIC INDICATORS OF HEALTH STATUS A food processing firm has used NHANES data to examine the effect of isotonic-beverage substitution on the nutrient intake of infants. A food company has used 24-hour recall data to compare the nutrient intake of infants fed formulas with that of infants fed cow's milk.
- 42 - A food Company has used food consumption pattern data, as well as physical measurements, to determine the nutritional status of pasta users and pasta nonusers. A university has used 24-hour recall and food-frequency data to determine the correlation between dietary intake (especially of iron) and biochemical indicators of health. A consulting firm has used NHANES data to prepare a brochure on nutrients in milk, with a focus on riboflavin and vitamin A intake and health status. A scientific association has used 24-hour recall data to study characteristics of persons and groups that consumed excess quantities of vitamins and minerals. DHHS has used data from NHANES II to establish baselines for monitoring progress toward "Nutrition Objectives for the Nation." EXAMINATION OF INTERACTIONS OF NUTRITION-RELATED VARIABLES WITH HEALTH CONDITIONS DETERMINED THROUGH HEALTH HISTORIES AND CLINICAL EXAMINATION . . . . The Food and Drug Administration is evaluating NHANES II data on iron, zinc, folacin, and vitamin A as part of a review of food fortification policy. A university has studied relationships among blood pressure and demographic, dietary, life-style, and anthropometric variables. A large food company has used biochemical, clinical examination, and anthropometric data to determine the consumption of specific foods and the potential toxic effects of food processing. University researchers have used NHANES data to study the association between nutrient intake and medical histories. In a collaborative project with NCHS, the Food and Drug Administration uses NHANES data to determine the prevalence of osteoporosis, the population groups at risk, and the possible need for calcium fortification in the food supply. A university has studied the relationship between periodontal,disease and vitamin C intake, with a focus on the possible benefits of megadoses. Researchers at the National Institute of Mental Health have used NHANES data to examine the relationship between consumption of coffee or tea and respondent-reported symptoms of anxiety. NCHS is studying the relationships among serum vitamin C, dietary vitamin C, use of dietary supplements, and cigarette-smoking.
43 DEVELOPMENT AND EVALUATION OF OTHER SURVEYS OR STUD IES THROUGH USE OF NHANES SURVEY METHODS AND DATA A private research institute has used the food-frequency form as a nutrition screening tool for the child and family support program. Nutrient intake data from NHANES were compared with data obtained from a southern county survey aimed at determining the dietary adequacy of low-income black families. In summarizing results from a small survey of nutrient intake of vitamins A, C, and D, riboflavin, and calcium, university scientists compared clinical signs of nutritional deficiencies from their survey with those of NHANES examinees. The Food and Drug Admini~ tration used NHANES consumption data to update the scientific data base in the Total Diet Study, especially on the most frequent ly consumed foods . A private research firm has used food-frequency questionnaires to collect data on food consumption patterns of the elderly and compared the results with NHANES data. USDA has used the dietary component instruments and data to collect and evaluate information from school nutrition and Women, Infants and Children's (WIC) programs. A university has used the food-frequency questionnaire and physiologic measurements in evaluating findings in a project to measure dietary iron and other factors related to hematocrit values of WIC participants. A private research foundation and a university have used the survey formats and have collected 24-hour recall data to assess dietary intakes of WIC (compared with non-WIC) participants. . The National Cancer Institute has used 24-hour recall data to compile a list of core foods for dietary questionnaires to be used in the cancer prevention program. A food manufacturer has used NHANES methods in assessing the value of data collected through other methods and surveys in estimating nutrient intakes. . A contractor for USDA has used the dietary data and other survey components to collect data and to assess the effectiveness of school nutrition progr ems . A consulting firm has used the NHANES dietary component to develop a study to evaluate the impact of "cashing out" of.food stamps for the elderly.
- 44 - - SU2~ARY Data from the 1976-1980 National Health and Nutrition Examination Survey (NHANES II) provided informs Lion on the total prevalence of disease conditions or physical states and on the interrelationships of health and nutrition variables in population groups. Data collection included sociodemographic information, a medical history, a physical examination by a physician, a dietary interview, and anthropometry. Clinical procedures and tests undertaken by NHANES II included x rays and numerous tests on samples of blood and urine. NHANES II was a probability sample of the civilian, noninstitutionalized population of the United States aged 6 months to 74 years . Populations of special nutritional interes t were overeampled, where necessary, to improve statistical reliability. In all, approximately 20,000 persons were interviewed and examined in NHANES II. Data were collected both by household interview and in mobile examination centers specially designed for cl inical examinations and procedures . Findings from the survey provided information on a wide range of health and nutrition issues, including measures of health and nutritional status of the U. S. population and specific groups . Repeated surveys provide a data base for estimates of changes over time.
