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Scientific Data Documentation
Hematology And Biochemistry, Version 2 (1976-1980)DSN: CC37.HANES2.HEMBIO2 NATIONAL HEALTH AND NUTRITION EXAMINATION SURVEY (NHANES II) HEMATOLOGY AND BIOCHEMISTRY Catalog Number 5411 Version 2 This data tape contains demographic data and blood and urine assessments for persons 6 months through 74 years of age examined in the second National Health and Nutrition Examination Survey (NHANES II), conducted during 1976-1980 by the National Center for Health Statistics, U.S. Public Health Service. A previous version of this tape with selected blood assessments was released in 1982. This version includes blood and urine assessments not previously released because of various methodological and analytical concerns. The user should pay close attention to the detailed notes which describe the issues or ploblems encountered with these assessments. HISTORY AND SCOPE 1. Description of Survey: NHANES II was one of a series of population based surveys conducted by the National Center for Health Statistics to help determine the heal th status of the Nation. Data were collected through response to questionnaires on medical history, food consumption, and health-related behavior. Data also were col1ected through direct medical examination. The tape documented here contains data from the demographic and physician examination parts of the survey for persons 6 months through 74 years of age. A detailed description of the design, content, questionnaires, and operation of NHANES II is provided in the following report: "Plan and Operation of the Second National Health and Nutrition Examination Survey, 1976-1980," DHHS Pub. No. (PHS) 81-1317, Vital and Health Statistics, Series 1, No. 15, Public Health Service, available at cost from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. The stock number is 01 7-022-00752-5. One copy is provided with the documentation herein, and a general summary of the data collection techniques and content is given in Appendix A. 2. Target Population: NHANES II was conducted on a nationwide probability sample of approximately 28,000 persons 6 months through 74 years of age from the civi1ian, noninstitutionalized population of the United States. The survey started in February 1976 and was completed in February 1980. The NHANES II sample was selected so that certain population groups thought to be at high risk of malnutrition (persons with low incomes, preschool children, and the elderly} were oversampled. Adjusted sampling weights were then computed for 76 age, sex, and race categories to inflate the sample in such a manner as to closely reflect the estimated civilian, noninstitutionalized U.S. population 6 months through 74 years of age at the midpoint of the survey (March 1, 1978). SAMPLE DESIGN Arid RECOMMENDATIONS FOR ANALYSIS NHANES II uses a multistage sample designed to represent the civilian, noninstitutionalized population of the United States, 6 months through 74 years of age. Since the sample is not a simple random one and certain population groups were oversampled, it is necessary to incorporate the person's sample weight for proper analysis of the data. The sample weight is a composite of the individual selection probability, adjustments for nonresponse, and poststratification adjustments. NHANES II provides information on 20,322 individuals who were both interviewed and examined, and on another 4,964 individuals who were i ntervi ewed but not exami ned, i n the age range 6 months through 74 years of age. In addition to the general examination components, several more detailed examinations were performed on subsamples of the population. Therefore, instead of there being one sample weight per person, there are several sample weights for each person. For a person not selected for a particular subsample, the associated subsample weight is zero. When analyzing the special subsamples, the analyst must be careful to select the appropriate sampling weight from the weights found in tape locations 282-317. For a more complete description of how the sample weights are calculated, see the detailed note section of this documentation. This file contains data on all 20,322 examined persons 6 months through 74 years of age. The NHANES II data were collected using a complex sample design involving both clustering and stratification. Because of the complex design and the ratio adjustments applied to the sample weights, the direct application of standard statistical analysis methods for variance estimation and hypothesis testing may be very misleading. The modification of statistical analysis procedures to incorporate the effects of complex survey designs is an important area of research; however, the current methodologies appropriate for the analysis of data from such surveys have not been made readily available in the standard packaged statistical software. There are computer programs available which provide the capability of variance estimation for complex sample designs. The balanced repeated replication approach(1) is utilized in &REPERR &PSALMS to calculate the variance-covariance matrix. Both routines are available within the OSIRIS IV library.(2) SURREGR(3) and SUPERCARP(4) are programs that calculate the variance-covariance matrix using the linearization approach(5) (Taylor series expansion). Another program, SESUDAAN(6), calculates variances and design effects. SURREGR and SESUDAAN are special procedures for the SAS package, which is available from SAS Institute, Box 8000, Carey, N.C., 27511. In order to provide the user with the capability of estimating the complex sample variances in the NHANES II data using the above procedures, Strata and Pseudo Primary Sampling Unit (PSU) codes have been provided on all data tapes in positions 324-326. These variables and the sample weights are necessary for the calculation of variances. Even though the overall number of examined persons in this survey is quite large for statistical inference purposes, subclass analyses can lead to estimators that are unstabl e, particularly estimates of variances. Consequently, analyses of subclasses require that the user pay particular attention to the coefficient of variation for the estimates of means, proportions and totals. In addition, small sample sizes, or a small number of PSU's used in the variance calculations, may produce unstable estimates of the variances using the above computer programs. An NCHS publication discusses these issues and describes analytic strategies for examining various hypotheses for the first National Health and Nutrition Examination Survey (NHANES I), which used a similar type of complex sample design.(7) HEMATOLOGY AND BIOCHEMISTRY, AGES 6 MONTHS - 74 YEARS DESCRIPTION This data tape contains demographic data and blood and urine assessments for all examined persons 6 months through 74 years of age. DEMOGRAPHIC DATA COLLECTION An advance letter, announcing the forthcoming arrival of an interviewer from the U.S. Bureau of the Census, was mailed to each household that fell into the NHANFS II probability sample. The interviewer subsequently visited the household to ascertain its composition, select the sample person(s), and administer demographic and medical history questionnaires. Demographic information relating to the household, the housing unit, and each sample person 6 months through 11 years of age was obtained from an available and competent household respondent. (In contrast, the preferred respondent for the medical information for persons 12 through 74 years of age was the actual sample person, with proxy response accepted when the sample person was not available.) BLOOD AND URINE ASSESSMENTS The blood and urine assessments were coil ected at the time of the medical examination in the Mobile Examination Center. They were analyzed in laboratories at a later time. Selected laboratory methods have been described elsewhere (see Reference No. 19). DATA QUALITY AND EDITING Extensive work was done to evaluate the quality control of the laboratories and to edit the blood and urine data. Whenever possible, data were checked for internal consistency. If any problems are found, please contact NCHS. INDEX TO TAPE POSITIONS Demographic Section Tape Positions a. Residence Data Sample Sequence Number ....................................... 1- 5 Catalog Number (5371-for Demographic Data only) .............. 6- 9 Unused position .............................................. 10 Size of place ................................................ 11 SMSA-not SMSA ................................................ 12 Unused positions ............................................. 13-23 Type of living quarters ...................................... 24 Land usage ................................................... 25 If rural, asked does this place have 10 acres or more? ....... 26 If 10 acres or more, asked if in the last 12 months did sales of farm produce and livestock amount to $50 or more? ...................................................... 27 If less than 10 acres, asked if in the last 12 months did sales of farm produce and live stock amount to $250 or more? ................................................... 28 Unused position .............................................. 29 Total number of persons in household ......................... 30-31 Total number of sample persons in household .................. 32-33 b. Sample Person Data Unused position .............................................. 34 Family relationship........................................... 35 Examination status ............................................ 36 Family unit number ............................................ 37-41 Unused positions ............................................. 42-44 Age-months (at interview) ..................................... 45-46 Age-years (at interview) ..................................... 47-48 Unused positions ............................................ 49-50 Date of birth-month ........................................... 51-52 Date of birth-year ........................................... 53-54 Sex .......................................................... 55 Race ......................................................... 56 . ............... In what State was he/she born? ............................... 57-58 Is he/she married, widowed, divorced, separated or never married? ......................................... 59 National origin or ancestry ................................... 60-61 Education level .............................................. 62-63 Grade completed .............................................. 64 What was he/she doing during most of the past 12 months? ..... 65 What was he/she doing? ....................................... 66 Did he/she work at a job or business at any time during the past three months? .............................. 67 Did he/she work full or part-time when working? .............. 68 Sample Person Data (Cont. } Tape Positions Was he/she working within last two weeks not counting work around the house? ............................ 69 Even though he/she did not work, does he/she have a job or business? ......................................... 70 Was he/she looking for work or on layoff from a job? ......... 71 Which - looking for work or on layoff from a job? ............ 72 What kind of industry or business is this? ................... 73-75 What kind of work was he/she doing? .......................... 76-78 Was he/she in private company or business or working for individual for wages, salary or commi ssi on? ................ 79 Did he/she ever serve in the armed forces of the U.S.? ....... 80 When did he/she serve? ....................................... 81 Unused positions ............................................. 82-90 c. Household Data How many rooms are in this? .... Count the kitchen, but not the bath ........................................... 91 How many bedrooms are in this? ............................... 92 Do you have complete kitchen facilities in your living quarters, that is a kitchen sink with piped water, a refrigerator and a range or cookstove? (Asked only of unrelated household members.) .............................. 93 Do you have access to complete kitchen facilities in this house? ............................................... 94 Do you have access to a range or cookstove? .................. 95 Do you have access to a refrigerator? ........................ 96 Do you have access to a sink with piped water? ............... 97 Is there piped water in this house (these living quarters }? ................................................ 98 Is there both hot and cold water? ............................ 99 Are these kitchen facilities used by anyone not living i n this household? ................................. 100 What is the main type of heating system you have? ............ 101-102 Do you have air conditioning? ................................ 103 How many motor vehicles are owned or regularly used for transportation by members of your family? .............. 104 Is any language other than English spoken by family members living here? ....................................... 105 What language? ............................................... 106 Which of these income groups represents your total combined family income for the past 12 months? ............. 107-108 Household Data (Cont.) Tape Positions During the past 12 months, how much money did you and all members of your family receive in wages or salaries before deductions (under $7,000 only)? ..................................................... 109-112 Social security or railroad retirement? ...................... 113 Unused position .............................................. 114 If yes, how much? ............................................ 115-118 Welfare payments or other public assistance? .................. 119 Unused position............................................... 120 If yes, how much? ............................................. 121-124 Unemployment compensation or workmen's compensation? ......... 125 Unused position .............................................. 126 If yes, how much? ............................................ 127-130 Government employee pension or private pensions? ............. 131 Unused position ............................................... 132 If yes, how much? ............................................. 133-136 Dividends, interest or rent? ................................. 137 Unused position ............................................... 138 If yes, how much? ............................................. 139-142 Net income from their own business (nonfarm), professional practice, or partnership? ..................... 143 Unused position ............................................... 144 If yes, how much? ............................................. 145-148 Net income from a farm? ....................................... 149 Unused position ............................................... 150 If yes, how much? ............................................. 151-154 Veteran's payments? ........................................... 155 Unused position ............................................... 156 If yes, how much? ............................................. 157-160 Alimony, child support or other support from persons not in household? .................................. 161 Unused position ............................................... 162 If yes, how much? ............................................. 163-166 Any other income? ............................................. 167 Unused position ............................................... 168 If yes, how much? ............................................. 169-172 Total amount ................................................. 173-176 Check Item B - Food stamps available ......................... 177 Are you certified to participate in the food stamp program? ........................................... 178 Are you buying food stamps now? .............................. 179 What is the main reason you are not participating in the program? .............................................. 180 Are you certified for commodity distribution program? ........ 181 Household Data (Cont.) Tape Positions Are you receiving commodity foods now for your fami1y? .................................................... 182 Why aren't you participating in the program? ................. 183 Date of exam ................................................. 184-189 Age in years (at examination) ................................ 190-191 Unused positions ............................................. 192-205 Race-sex recode for sample persons ........................... 206 Farm, nonfarm recode for sample person ....................... 207 Interview status ............................................. 208 Region ....................................................... 209 Poverty index ................................................ 210-212 Unused positions ............................................. 213-246 Head of Household Data Age in years ................................................. 247-248 Unused positions ............................................. 249-250 Date of birth-month ........................................... 251-252 Date of birth-year ........................................... 253-254 Sex .......................................................... 255 Race ......................................................... 256 In what State was he/she born? ............................... 257-258 Is he/she married, widowed, divorced, separated or never married? .......................................... 259 National origin or ancestry? ................................. 260-261 Education level .............................................. 262-263 Grade completed .............................................. 264 What was he/she doing most of the past 12 months? ............ 265 What was he/she doing? ....................................... 266 Did he/she work at job or business during past three months? .............................................. 267 Did he/she work full or part-time when working? .............. 268 Did he/she work at any time the last two weeks not counting work around the house? ........................ 269 Even though he/she did not work, does he/she have a job or business? .................................... 270 Was he/she looking for work or on layoff from a job? ......... 271 Which - looking for work or on layoff from a job? ............ 272 Type of industry or business ................................. 273-275 What kind of work was he/she doing? .......................... 276-278 Was he/she in private company or business or working for individual for wages, salary or commission? ............ 279 Did he/she ever serve in the armed forces of the U.S.? ....... 280 When did he/she serve? ....................................... 281 Sample Weight Section Tape Positions Examined final weight ........................................ 282-287 Medical history interview final weight ....................... 288-293 Glucose Tolerance Test final examined weight ...................................................... 294-299 Lead final examined weight ................................... 300-305 Carboxyhemoglobin final examined weight ....................... 306-311 Bile acids final examined weight .............................. 312-317 Unused positions ............................................. 318-323 Strata code .................................................. 324-325 Pseudo PSU code .............................................. 326 Poverty Non-Poverty Segments ................................. 327 Serum ferritin final examined weight ......................... 328-333 Folates, Vitamin B12 and differential counts final examined weight ............................................ 334-339 Unused positions ............................................. 340-350 Blood and Urine Data Section Catalog number ................................................ 351-354 Specimen collection ........................................... 355 Session ....................................................... 356 Hematocrit .................................................... 357-359 Hematocrit imputation code .................................... 360 Hemoglobin .................................................... 361-363 Hemoglobin imputation code .................................... 364 Red blood cell count .......................................... 365-367 White blood cell count ........................................ 368-370 Mean corpuscular volume ....................................... 371-374 Mean corpuscular hemoglobin ................................... 375-377 Mean corpuscular hemoglobin concentration ..................... 378-380 Serum iron .................................................... 381-383 Serum total iron-binding capacity .............................. 384-386 Transferrin saturation ......................................... 387-389 Serum albumin .................................................. 390-392 Serum vitamin C ................................................ 393-395 Serum zinc ..................................................... 396-398 Serum copper ................................................... 399-401 Serum vitamin A ................................................ 402-404 Erthyrocyte protoporphyrin ..................................... 405-408 Lead ........................................................... 409-411 Carboxyhemoglobin .............................................. 412-415 Methemoglobin ................................................. 416-419 Carboxyhemoglobin imputation code ............................. 420 Blood and Urine Data Section (Contd.) Serum lipids, lipoprotein and related data ...................... 421-439 Oral glucose tolerance related data ............................. 440-464 Oral glucose challenge results .................................. 465-474 Serum ferritin .................................................. 475-478 RBC folate ...................................................... 479-482 Serum folate ..................................................... 483-486 Serum B12 ....................................................... 487-490 Differential counts ............................................. 491-510 Serum creatinine ................................................ 511-513 Urine multistix test results .................................... 514-521 Bile acid data .................................................. 522-527 Unused positions ................................................ 528-530 USE OF SPECIAL TERMLS For the demographic data, the term "blank but applicable", is used to indicate a data item that was to have a response for a sample person but for which no usable data were provided. This includes unanswered data fields, as well as those containing impossible entries: i.e., out-of- range or inconsistent with other entries. The term "blank" refers to data items where the sample person was not supposed to respond to the question. The notation "see detailed note" is intended to refer the user to the section Detailed Notes. In this section, a comprehensive description of the field is given. DETAILED NOTES TAPE POSITION 11 Size of Place Size of place classification was derived from the 1970 decennial census of the population. According to the definition used in the 1970 census, the urban population comprised all persons living in (a) places of 2,500 inhabitants or more incorporated as cities, boroughs (except Alaska), villages and towns (except towns in New York, New England states, and Wisconsin), but excluding those persons living in the rural portions of extended cities; (b) unincorporated places of 2,500 inhabitants or more; and (c) other territories included in urbanized areas. The remaining population was classified as rural. Urban areas are further classified by population size for places within urbanized areas and other places outside urbanized areas. TAPE POSITION 12 SMSA-Not SMSA Except in New England, a Standard Metropolitan Statistical Area is basically a county or a group of contiguous counties which contains at least one city of 50,000 inhabitants or more, or "twin cities" with a combined population of at least 50,000. In addition to the county or counties containing such a city or cities, contiguous counties are included in an SMSA if, according to the 1970 census, they are socially and economically integrated with the central city. Each SMSA must include at least one central city, and the complete title of an SMSA identifies the central city or cities. In New England, SMSA's consist of towns and cities, rather than counties. TAPE POSITIONS 37-41 Family Unit Number All related sample persons in the same family unit have the same computer- generated family unit code. This will enable analysis of individual family units. TAPE POSITIONS 56, 206, AND 256 Race The race of the respondent was marked by observation. The interviewers were instructed to assume that the race of all related persons was the same as the respondent unless otherwise learned. The race categories were "White", "Black" or "Other". If the appropriate category could not be marked by observation, then race was asked. Interviewers were instructed to record persons who responded with something other than White or Black, such as Japanese, Chinese, American Indian, Korean, Hindu, Eskimo, etc. as "Other" and to include Mexicans, Puerto Ricans and other persons of Latin American descent in "White" unless definitely Black, American Indian, or of other nonwhite race. TAPE POSITIONS 57-58 AND 257-258 United States Name of Place Alabama .............................................. 01 Alaska ............................................... 02 Arizona .............................................. 04 Arkansas ............................................. 05 California ........................................... 06 Colorado ............................................. 08 Connecticut .......................................... 09 Delaware ............................................. 10 District of Columbia ................................. 11 Florida .............................................. 12 Georgia .............................................. 13 Hawaii ............................................... 15 Idaho ................................................ 16 Illinois ............................................. 17 Indiana .............................................. 18 Iowa ................................................. 19 Kansas ............................................... 20 Kentucky ............................................. 21 Louisiana ............................................ 22 Maine ................................................ 23 Maryland ............................................. 24 Massachusetts ........................................ 25 Michigan ............................................. 26 Minnesota ............................................ 27 Mississippi .......................................... 28 Missouri ............................................. 29 Montana .............................................. 30 Nebraska .............................................. 31 Nevada .............................................. 32 New Hampshire ........................................ 33 New Jersey ........................................... 34 New Mexico ........................................... 35 New York ............................................ 36 North Carolina ........................................ 37 North Dakota ......................................... 38 Ohio ................................................. 39 Oklahoma .............................................. 40 Oregon ................................................ 41 Pennsylvania .......................................... 42 Rhode Island .......................................... 44 South Carolina ........................................ 45 South Dakota .......................................... 46 Tennessee ............................................. 47 Texas ................................................. 48 Utah ................................................. 49 Vermont .............................................. 50 Virginia ............................................. 51 Washington ........................................... 53 West Virginia ........................................ 54 Wisconsin ............................................ 55 Wyoming .............................................. 56 Outlying Areas of the United States Name of Place Code Description American Samoa 60 U.S. territory in the Pacific Canal Zone 61 Territory in Panama leased by U.S. Canton and Enderbury Island 62 Under common US-UK administration Guam 66 U.S. territory in the Pacific Johnston Atoll U.S. territory in the Pacific, includes Sand Island Midway Islands 71 U.S. territory in the Pacific Puerto Ri co 72 Commonwealth associated with the U.S. Swan Islands 74 U.S. territory in the Carribean Trust Territories of the 75 U.S. administered, includes Pacific Islands Caroline, Mariana, and Marshall Island groups U.S. Miscellaneous Carribean 76 Includes Navassa Islands, Quito Islands Sueno Bank, Roncador Cay, Serrana Bank, Serranilla Bank U.S. Miscellaneous Pacific 77 Includes Kingman Reef, Howland, Islands Baker and Jarvis Islands, Palmyra Atoll Virgin Islands 78 U.S. territory in the Carribean Wake Island 79 U.S. territory in the Pacific Outside of United States North America 91 South America 92 Europe 93 Africa 94 Asia 95 Australasia 96 Pacific Islands 97 TAPE POSITIONS 73-75, 76-78, 273-275 AND 276-278 Industry and Occupation Codes Occupation may be defined as the principal job or business. For this survey, the principal job or business of a respondent is defined in one of the following ways: if the person worked during the two week interview period or had a job or business, the question concerning occupation (or work} applies to the job during that period. If the respondent held more than one job, the question is directed to the one at which the most time was spent. It refers to the one considered most important when equal time is spent at each job. A person who has not begun work at a new job, is looking for work, or is on layoff from work is questioned about the last full-time civilian job. A full- time job is defined as one at which the person spent 35 or more hours per week and which lasted two consecutive weeks or more. A person who has a job but has not yet reported to it or a person who has never had a job or business is classified as a "new worker" The 1970 census of population Alphabetical Index of Industries and Occupations was used in the coding of both the industry and occupation (Library of Congress Number 74-612012, for sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Stock Number 0301-2283). TAPE POSITIONS 107-108 Family Income Group The respondent was handed a card with twelve income ranges listed as Group A to Group L and asked "Which of these income groups represents your total combined family income for the past 12 months, that is, yours, your ...'s, etc? Include income from all sources such as wages, salaries, social security or retirement benefits, help from relatives, rent from property and so forth." If the respondent answered Group A through G, that is with an income less than $7,000, then questions 21 and 22 detailing exact sources and amounts of income were asked; otherwise, these questions were skipped. No effort was made to reconcile amounts reported in detailed questions 21 and 22 with the categorical response to the family income group question. During the survey time period no adjustments to the income groups or $7,000 value were made to account for inflation. TAPE POSITION 207 Farm, non-farm This position contains a recode, which combines data on land use (position 25), size (position 26), and amount of sales of farm produce and livestock (positions 27 and 28). Code 1: Farm: Rural land (coded 2 in position 25) which consisted of 10 or more acres (coded 1 in position 26) with crop sales of $50 or more (coded 1 in position 27). OR Rural land (coded 2 in position 25) with crop sales of $250 or more (coded 1 in position 28). Code 2: Non-farm: All other rural land (coded 2 in position 25) as well as land classified as urban (coded 1 in position 25). TAPE POSITION 209 Region The United States was divided into four broad geographic regions of approximately equal population. Those regions, which deviate somewhat from the groups used by the Bureau of Census, are as follows: Region States Included Northeast Maine, Vermont, New Hampshire, Massachusetts, Connecticut, Rhode Island, New York, New Jersey, and Pennsylvania South Delaware, Maryland, District of Columbia, West Virginia, Virginia, Kentucky, Tennessee, North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and Arkansas Midwest Ohio, Illinois, Indiana, Michigan, Wisconsin, Minnesota, Iowa, Missouri West Washington, Oregon, California, Nevada, New Mexico, Arizona, Texas, Oklahoma, Kansas, Nebraska, North Dakota, South Dakota, Idaho, Utah, Colorado, Montana, Wyoming, Alaska, Hawaii TAPE POSITIONS 210-212 Poverty Index Income status was determined by the Poverty Income Ratio (PIR). Poverty statistics published in the Bureau of the Census reports(10-14) were based on the poverty index developed by the Social Security Administration (SSA) in 1964. (For a detailed discussion of the SSA poverty standards, see references 15 and 16.) Modifications in the definition of poverty were adopted in 1969.(17) The standard data series in poverty for statistical use by all executive departments and establishments has been established.(18) The two components of the PIR are the total income of the household (numerator: the median of the income group for incomes $7,000 and above; the sum of the component parts of the income questions for incomes under $7,000) and a multiple of the total income necessary to maintain a family with given characteristics on a nutritionally adequate food plan(9-13) (denominator). The dollar value of the denominator of the PIR is constructed from a food plan (economy plan) necessary to maintain minimum recommended daily nutritional requirements. The economy plan is designated by the U.S. Department of Agriculture for "emergency or temporary use when funds are low." For families of three or more persons, the poverty level was set at three times the cost of the economy food plan. For smaller families and persons living alone, the cost of the economy food plan was adjusted by the relatively higher fixed expenses of these smaller households. The denominator or poverty income cutoff adjusts the family poverty income maintenance requirements by the family size, the sex of the family head, the age of the family head in families with one or two members, and the place of residence (farm, nonfarm). Annual revisions of the poverty income cutoffs are based on the changes in the average cost of living as reflected in the Consumer Price Index. As shown in the tabl es, the annual income considered to be the poverty level increases as the family size increases. A family with any combination of characteristics and with the same income as shown in the table has been designated as having a PIR or poverty level of 1.0. The same family with twice the income found in the table would have a PIR of 2.0. Ratios of less than 1.0 can be described as "below poverty" and ratios greater than or equal to 1.0, as "at or above poverty". Poverty thresholds are computed on a national basis only. No attempt has been made to adjust these thresholds for regional, State, or other variations in the cost of living (except for the farm, nonfarm difference). None of the noncash public welfare benefits such as food stamp bonuses are included in the income of the low income families receiving these benefits. PIR has been adjusted by year (see tables) and accounts in some part for inflation. TAPE POSITIONS 2~2-317 Sample Weights A multistage estimation procedure was used to calculate the various NHANES II subsample sample weights that are necessary to use in any analysis of the data. The procedure has three basic components: 1) inflation by reciprocals of the probabilities of selection, 2) adjustment for nonresponse, and 3) poststratification ratio adjustment by age-sex-race. A brief description of each component is as follows: Inflation by reciprocals of the sampling probabilities. Since the survey utilized a three-stage sample design, there were three probabilities of selection: 1) the probability of selecting the PSU, 2) the probability of selecting a segment and housing unit, and 3) the probability of selecting a sample person. Adjustment for nonresponse. Estimates from the NHANES II data were adjusted to account for sample persons who were not examined. The estimates were inflated by a multiplication factor calculated within five selected income groups, three age groups, four regions, and standard metropolitan statistical area {SMSA) or non-SMSA. The numerator of these factors was the sum of the weights for sample persons resulting from the reciprocal of the probability of selection, and the denominator was the sum of the weights for examined persons also resulting from the reciprocals of the sampling probabilities. Poststratification by age-sex-race. The estimates were ratio adjusted within each of 76 age-sex-race cells to an independent estimate, provided by the U.S. Bureau of the Census, of the population of each cell as of March 1, 1978, {approximate mid-point of the survey). The ratio adjustment was a multiplication factor of which the numerator was the U.S. population and the denominator was the sum of the weights adjusted for nonresponse for examined persons. This ratio estimation process makes the sample more closely representative of the civilian, noninstitutionalized population of the U.S. Potential bias of nonresponse. Usually a sizeable number of sample persons who initially are willing to complete the household information and some of the medical history questionnaire subsequently will not participate in the examination. This creates the potential for bias if these persons differ from other sample persons with respect to the variables being studied. Intense efforts were undertaken during NHANES II to develop and implement standard procedures and inducements that would reduce the number of nonrespondents and thereby reduce the potential for bias. The user needs to be aware of and should explore the potential bias for nonresponse in any analysis of the NHANES II data. TAPE POSITIOIN 327 Poverty, Non-poverty segments In order to oversample persons with low incomes, enumeration districts (ED's) were sorted into poverty or non-poverty strata as follows: the poverty strata contained ED's with 13 percent or more of persons below the poverty level, and the non-poverty strata contained ED's with less than 13 percent of persons below the poverty level as determined by the 1970 census. Thus, segments (cluster of housing units} within ED's were classified as either poverty or non-poverty. TAPE POSITIONS 328-339 Special Subsample Weights Two special subsample weights are found in these tape positions. A procedure similar to that explained in the detailed note for tape positions 282-317 was used to calculate these sample weights. See the detailed note for tape positions 475-510 for the appropriate use of these subsample weights in analysis of the data for serum ferritin, serum vitamin B12, serum folate, red blood cell folate, and differential leukocyte counts. TAPE POSITION 355 Specimen Collection In NHANES II, there were 1,337 sample persons for which there is no blood or urine data. These were persons who either refused the venipuncture, had an unsuccessful venipuncture, or were excused for some special circumstances. TAPE POSITIONS 357-380 Hematological Assessments The hematology measurements were done in the mobile examination center. Hemoglobin assessments were performed on a Coulter hemoglobinometer. Hematocrit measurements were performed by the spun microhematocrit method. Cell counts were performed on a Coulter Model FN. The hematologic indices (MCV, MCH, MCHC) were computer generated using the spun microhematocrit value and, the following formulas: MCV (in femtoliters) = Hematocrit (percent) / RBC per liter x 100 MCH (in picograms) = Hemoglobin (g/ dl) x 10 / RBC per liter MCHC (in g/ dL) = Hemoglobin (g/ dl) x 100 / Hematocrit (percent) If either hemoglobin or hematocrit values were missing but not both, then an imputed value was calculated for the missing item using the other known value. This was done for 30 hematocrit values and 535 hemoglobin values. No imputation were done if both items were missing. The following mathematical formulae were used in the imputation procedure: (1) Hemoglobin missing: Hemoglobin = 0.3448 x Hematocrit (2) Hematocrit missing: Hematocrit = 2.9 x hemoglobin TAPE POSITIONS 409-411 Lead Sample The NHANES II Lead subsample consisted of all sample persons ages 6 months - 6 years and one-half of all sample persons ages 7-74 years. Those sample persons no in the Lead subsample have a value of 999 in tape positions 409-411. TAPE POSITONS 412-415, 416-419 Carboxyhemoglobin Subsample The NHANES II carboxyhemoglobin subsample consisted of one-half of all sample persons ages 3-74 years. Those persons not in the carboxyhemoglobin subsample have "9999" in each of these two tape locations. Carboxyhemoglobin and methemoglobin level measurements were made by the spectrophotometric method of Small et al.(1) 1 Small, K.A., Radford, E.P., Frazier, J.M., and others: A rapid method for simultaneous measurement of carboxy-and-methemoglobin in blood. J. Appl. Physiol. 31: 154-160, 1971. TAPE POSITION 420 Carboxyhemoglobin Imputation The carboxyhemoglobin imputation codes identifies those cases where an absent or unacceptable carboxyhemoglobin value (pos. 412-415) was replaced by an acceptable value from a demographically similar examinee. Whenever a carboxyhemoglobin value was imputed, the corresponding methemoglobin value (pos. 416-419) was also imputed. A "0" in this position indicates imputed values while a "1" indicates nonimputed values. A "9" indicates that this examinee was not selected to receive a carboxyhemoglobin evalutaion. In a few cases, a valid carboxyhemoglobin value did not have any methemoglobin value recorded with it; in these cases, the methemoglobin value was not imputed. TAPE POSITIONS 421-423, 426-429, and 434-437 Serum Lipid Determinations Blood samples were obtained by venipuncture from both fasting and nonfasting subjects. The cells were allowed to clot and the samples were then centrifuged. The serum was recovered, and aliquot was placed in a plastic screw-capped vial and placed in a freezer within three hours of collection. At approximately two-week intervals, serum specimens collected over the preceding period were placed in a styrofoam shipping container containing dry ice and shipped to George Washington University Lipid Research Clinic Laboratory for analysis of serum cholesterol, triglyceride and high density lipoprotein (HDL) cholesterol. Samples received in the laboratory were placed in a freezer at -15 degrees until they were analyzed; usually within two weeks of receipt. Specimens were allowed to thaw at room temperature and them mixed thoroughly by vortexing. All measurements were performed according to the protocol described for the Lipid Research Clinics (LRC) program. (1) Total Serum Cholesterol and Serum Triglycerides Analyses were performed on zeolite-treated isopropanol extracts using a Technicon Auto-Analyzer II (AAII) which uses a Lieberman-Burchard reagent for cholesterol and a flourimetric measurement of triglycerides. Instrumental process was established at the beginning of each analytical run with cholesterol/triglyceride standards in isopropanol (100/50, 200/100, 300/200 and 400/300 bg/dL) provided by the Clinical Chemistry Standardization Section of the Centers for Disease Control (CDC). A serum calibrator was used to automatically adjust instrumental response to reference Abell-Kendall values.(2) Extracts of a high or low serum cholesterol/triglyeride internal pool were positioned in each tray; results from out-of-control analyses were rejected and the analyses repeated. The serum calibrator and internal control pools with assigned cholesterol/triglyceride target values were provided by the CDC. High Density Lipoprotein Cholesterol HDL cholesterol was determined by the beta quantification procedure, which involves a combination of preparative ultracentrifugation and heparin-maganese precipitation. The determination was made on a supernatant fraction obtained after treatment of the sera with heparin and manganese chloride, to precipitate apo B containing lipoprotein. The precipitate was sedimented by centrifugation for 30 minutes at 1500 x g, and an aliquot of the clear supernatent was extracted with 9.5 volumes of 99 percent isopropanol. The extract was treated with a zeolite-containing mixture to remove interfering substances. The solids were sedimented by centrifuging for 30 minutes at 1500 xg, and the cholesterol content of the extract was measured on the AutoAnalyzer II (Technicon Instruments, Tarrytown, N.Y.) as described in the LRC Program Operations Manual.(1) 1 Manual of Laboratory Operations, Volume I, Lipid Research Clinics Program, Lipid and Lirpoprotein Analysis. DHEW Publications No. (NIH) 75-628, 1974. 2 Bachorik P.S., Wood PDS, William J., Kuchmak M., Ahmed S. et al: Automated determinations of total Plasma Cholesterol: A Serum Calibration technique Clin. Chem. Acta. 96:145, 1979. TAPE POSITION 424 Lipids Imputation Process The 272 missing serum cholesterol values were imputed using a "hot deck" procedure. The variables used in the imputation process were sex, age, and for women, hormone/birth control pill use. Since less than one percent of males in NHANES II were taking hormones, the hormone variable was not used for imputing the missing values for males. Consequently, the variables used in the imputation process for each sex are as follows: Males Females (a) age (a) age (b) birth control pill use The serum cholesterol file for males was sorted by age. The serum cholesterol file for females was divided into pill and non-pill users, then each file was sorted by age. When a missing cholesterol value was encountered, the preceding sample person's value of the smae age was substituted. If there were consecutive missing values, an iterative process was used to assure that the preceding value was substituted only once. No imputations were performed for serum triglycerides of HDL cholesterol. TAPE POSITION 425 Birth Control Pill Usage The birth control pill question was worded as follows: (a) Have you taken birth control pills during the past six months? Only if the answer to this question was yes, was the sample person asked: (b) Are you taking them now? There were 533 females ages 20-74 years who were interviewed as part of the Health History Supplement of the Medical History for NHANES II that answered "yes" to both questions. TAPE POSITIONS 426-429, 430-433 Serum Triglyceride Serum Triglyceride values in positons 426-429 are for the fasting sample only. The nonfasting sample values are indicated as 9999. There were 5903 sample persons in the fasting sample. The fasting time in hours were calculated from the Glucose Challenge and Related Diabetes Data questionaire and are recorded in positions 430-431 and recoded in position 432. The questions were as follows: a. How many hours ago did you have your last meal? b. Have you had anything to eat or drink, except water, since that meal? c. How many hours ago did you have it? Note: Question "c" was only asked of those sample persons who answered "yes" to question "b." If the answer to question (b) was "yes", then the fasting time was recorded from the answer to question (c); otherwise, the number of fasting time was recorded from the answer to question (a). The analyst should use the information on actual fasting time (positions 430- 431 or 432) and information on time of examination, morning, afternoon or evening (position 433) to determine legitimate triglyceride values since there are sample persons who have fasting times less than 10 hours or who were examined in the afternoon or evening. TAPE POSITIONS 438-439 HDL Cholesterol Strata Code for Variance Calculation The strata codes in positions 438-439 should be used when calculating complex sample variance estimates for HDL cholesterol only. For other variables on this tape, use strata codes as recorded in positions 324- 325. TAPE POSITIONS 440-474 OGTT and Blood Glucose Analysis OGTT's were administered according to National Diabetes Data Group (NDDG) recommendations, which require the following: Subjects fast overnight for 10- 16 hours; OGTT's are performed in the morning; a fasting blood sample is taken; subjects drink flavored water containing 75 grams of glucose or carbohydrate equivalent; and additional blood samples are taken. The drink used in HANES II was Glucola,(a) a cola-flavored preparation containing a carbohydrate equivalent of 75 grams of glucose. Although the NDDG recommends that blood samples be taken at one-half hour intervals up to the final 2-hour sample, in this voluntary survey NHANES II fields staff did not attempt to obtain multiple midtest venipunctures. (The test recommended by the World Health Organization requires only fasting and 2-hour blood samples.) The did obtain fasting, single midtest, and 2-hour blood samples in 98 percent of OGTT's in compliance with NDDG guidelines. More than 95 percent of all midtest and 2-hour samples were obtained within 5 minutes of the specified times, and 99 percent were within 10 minutes. Venous blood samples were obtained in each venipuncture. Plasma was seperated from blood, frozen, and shipped in dry ice to the Centers for Disease Control for analysis. There, glucose determinations were made by the Clinical Trials Section, Metabolic Biochemistry Branch, Clinical Chemistry Division, using a microadaptation of the national glucose reference method. This method has been shown to have several desirable properties including reliability, transferability, specificity, and precision. It has an average bias of less than 2 percent. Further information on precessing of blood samples and the classification and diagnosis of diabetes mellitus is presented in Series 11 Number 237, available from the National Center for Health Statistics. This report also presents an indepth analysis of the possible effects (bias) due to the large amount of missing data for this topic area. a Mention of brand names is for the purpose of specific indentification of the equipment or product used in the survey and does not imply endorsement by the U. S. Department of Health and Human Services. TAPE POSITIONS 475-478, 479-482, 483-486, 487-490, 491-510 Ferritin, Folate, B12, and Differential Count Subsamples In HANES II, the following assessments were done on a special subsample of persons ages 3-74 years from the total examined sample; serum ferritin, serum vitamin B12, serum folate, red blood cell folate, and differential leukocyte counts. This subsample, (sometimes referred to as the "anemia" sample), was defined as a random ten percent sample of all examined sample persons plus all persons who had a predetermined "high" or "low" value for one or more of the following hematologic assessments: hemoglobin, hematocrit, red cell count, white cell count and mean corpuscular volume. The number of examined sample persons in this subsample was 3,909. For each assessment there were a number of persons who do not have a known value (for numerous reasons) and these are designated by blank but applicable codes. Because the sample size was relatively small to begin with and because of larger numbers of missing values for these assessments, extra caution needs to be used when any analyses of these data are done. A special sample weight was calculated for use in analysis of these data (except ferritin, see below). It is located in tape positions 334-339. Because this sample weight is based on relatively few people, the population point estimates and standard errors will be much more variable and unstable. This will often limit the presentation and interpretation of the data. Do not use the sample weight found in tape positions 282-287. This latter sample weight is appropriate to use for other blood and urine assessments on this data tape. For serum ferritin, an additional subsample of persons were selected and analyzed in the laboratory. Therefore there were 5,833 examined sample persons in the "ferritin subsample." Of these, 5157 have a known result. A seperate sample weight was calculated for this special subsample and is found in tape positions 328-333. Again, this is the only appropriate sample weight to use when analyzing the serum ferritin data. The original protocol stated that all of the above assessments (except ferritin) were to be done for all age groups. Because of the difficulty in drawing blood from young children, these subsample assessments were only reported for ages 3-74. In addition to the sample size issue, missing data and methodological issues are significant for each of the assessments listed above. Examples of these issues for the folate and iron assessments have been published(1,2) and should be reviewed by users before conducting analyses using these measures. 1 Expert Scientific Working Group. Summary of a report on assessment of iron nutritional status of the United States population. Am J Clin Nutr 1985:42:1318-30. 2 Senti FR and Pilch SM, editors. Analyses of folate data from the second National Health and Nutrition Examination Survey (NHANES II) J. Nutr. 1985:115:1398-1402. TAPE POSITIONS 511-513 Serum Creatinine Serum creatinine determinations were performed by Western Laboratories (Jaffle Reaction Smac Technicon). All specimens of serum yielding creatinine values for 1.4 mg/100 ml or greater had an immediate repeat determination. The two values were then averaged, with odd identificator numbers rounded up and even identification numbers rounded down. Records showing individual values for the quality control standards were available only for part of the survey. The time period of September 1977 to December 1978 was used to evaluate the overall quality of the data since it contained the greatest number and most consistent coverage of the available quality control determinations. There were no values of the quality control standards run during this period that fell outside the designated range of 1.3 to 1.8. The overall mean of the quality control standards (Monitrol) during that period was 1.58 as compared to an expected mean of 1.55. After the survey was completed the creatinine data were subjected to further editing to eliminate erratic laboratory runs. The editing procedure used a technique involving truncated means adjusted for age and sex to detect out-of-range laboratory runs. This resulted in an elimination of 249 serum creatinine values from those collected on the 18-74 year age group. The nonresponse rate for serum creatinine was 28.3 percent. The reasons for item nonresponse for serum creatinine included: refusal to give blood and technical failures in blood drawing and handling of the specimens (3%), low priority given to this determination resulting in lack of serum (10-11%), and editing exclusion of erratic laboratory runs (2%). The remainder of the item nonresponse for serum creatinine can be attributed to loss of specimens in shipping (13%). A large part of this shipping loss resulted from misdirection by the post office of serum from CDC to Western Laboratories. Because of the large amoung of missing data and the lack of quality control data for part of the laboratory analyses, users are urged to be extremely cautious in analyzing and interpreting the findings for serum creatinine. TAPE POSITIONS 514-521 N-Multistix Test Results Urinalysis Ames Reagent Strips were used to test for the presence of glucose, bilirubin, ketone, blood, pH, protein, nitrite and urobilinogen in the urine. These test results may provide information regarding the status of carbohydrate metabolism, kidney and liver function, acid-based balance, and urinary tract infection. Procedure used for testing urine 1. Fresh urine specimen was collected in a clean, dry container. The urine was mixed well immediately before testing. 2. A reagent strip was replaced immediately. Reagent areas of the strip were completely immersed in the fresh urine and removed immediately to avoid dissolving out the reagents. 3. Excess urine was removed from the strip by running the edge of the strip against the rim of the urine container. The strip was held in a horizontal position to prevent possible areas and/or contaminating the hands with urine. 4. The reagent areas were compared to the corresponding color chart on the bottle label at the time specified. The strip was held close to the color blocks and watched carefully. Care was taken so that the strip was not laid on the color chart because this would result in the urine soiling the chart. For more information on the specific procedure for each test, users may contact the National Center for Health Statistics or The Ames Division, Miles Laboratories, Inc., P.O. Box 70, Elkhart, Indiana 46515. TAPE POSITIONS 522-527 Serum Bile Acid Information Two-hour postprandial serum bile acids (SBA) were measured on a subsample of adults ages 35-74 years in NHANES II. Sample persons were administered X-NOG, a high-fat eggnog drink containing approximately 8.6 percent full milk cream and egg yolks (manufactured by Syntex Lab, Palo Alto,CA), or the substitute (peanut butter cups) if an egg allergy was present. Two hours (+- 30 minutes) after ingestion of the challenge, the blood sample was taken. The blood samples were analyzed at the Division of Gastroenteroloby's laboratory at the New York Hospital-Cornell Medical Center in New York City. Postprandial SBA were measured fluorometrically by means of an enzymatic technique with strict quality control. Of the 4,089 adults in the bile acids sample, 3261 (80 percent) had a SBA value available for analysis. About half of the missing data was due to a loss of blood shipment for the first five locations in the survey. The rest of the missing data was due to a variety of reasons including: refusal to have the blood drawn, and allergy to the challenge drink, insufficient amount of sera, etc. Users should be cognizant of the potential bias these missing data may have on the analysis and presentation of serum bile acids results.
