NLSY79

• Retention vs response rate
• Reasons for non-interview (RNI)

Retention vs. response rate

Retention rates for NLSY79 respondents from 1979 to 1993 exceeded 90 percent. Rates from 1994 until 2000 exceeded 80 percent. Rates from 2002 until 2014 were in the 70s. Retention rate is calculated by dividing the number of respondents interviewed by the number of respondents remaining eligible for interview. All 1979 (round 1) respondents including those reported as deceased are eligible for interviews, with the exception of those who have been permanently dropped from the sample. In the round 30 (2022) survey, 6,413 civilian and military respondents out of the 9,964 eligible were interviewed, for an overall retention rate of 64.4 percent. Retention rates for each survey are shown in Table 1.

The number of respondents can also be expressed as a percentage of the number of base year respondents not known to be deceased. This is referred to as the response rate and is reported in Table 2 for each survey round. As of 2022, 1,348 main respondents had been reported as deceased. The response rate for those believed to be alive is 74.4 percent.

Reasons for non-interview (RNI)

A 'Reason for Noninterview' variable is constructed for each survey year (excluding 1979) in the NLSY79 and provides an explanation of why an interview could not be conducted or completed with a respondent. The cause of noninterview is assigned by the NORC interviewer to each respondent designated as a member of the eligible sample for a given survey year. Typical coding categories have included reasons such as an interview being refused by the respondent or by the respondent's parent, the respondent or family unit not being located, or the respondent being reported as deceased.

Beginning in the 1980s, two administrative categories were added. One reflected a decision by NORC not to attempt to interview certain sample members who were determined to be extremely difficult to interview. The second category indicates that, due to funding cutbacks, interviews would not be attempted with certain members of one or more of the NLSY79 subsamples. Thus, beginning in 1985, interviews ceased for 1,079 respondent members of the military subsample; each was permanently assigned a reason for noninterview of "military sample dropped." A second group of respondents, those belonging to the supplemental economically disadvantaged, nonblack/non-Hispanic sample, was similarly dropped from interviewing beginning with the 1991 survey. The target universe for each survey year--that is, the respondents whom NORC attempts to interview--thus includes all respondents interviewed in the initial survey year exclusive of those who were:

1. reported deceased at an earlier interview
2. dropped from the sample
3. judged to be extremely difficult to interview

Table 3 presents the number of respondents not interviewed across survey years by sample type.

Sample representativeness and attrition

This section reviews the number of respondents who have continued to be interviewed during all surveys. Table 4 shows the number of respondents, excluding dropped respondents, who were interviewed at all survey points. This table exhibits the high degree of NLSY79 retention. From 1979 to 2022 the survey has been administered 30 times.

Table 5 shows the distribution of the number of interviews completed by respondents, broken down by sample type. The "Number who Completed" column shows how many respondents completed exactly that number of surveys. These numbers refer to any surveys completed since the NLSY79 began, not necessarily consecutive surveys completed or surveys completed in particular years. The cumulative percent column shows a cumulative total percent of those completing at least a given number of surveys rather than a percentage of those completing an exact number of surveys. Readers should note the attrition suggested in Table 4 greatly overstates the amount of lost information. The NLSY79 asks detailed questions about work history, education, training, marital status, and fertility since the date of the respondent's last interview. These retrospective questions capture information lost due to missed interviews. Hence, a perfect response record is not needed for researchers to understand how the respondent's life changes over time, unless he or she leaves the survey forever.

• Interview methods and target universe
• Interview schedule and fielding periods

Interview methods and target universe

During each survey round, NORC attempts to reach all youth within the active samples. No respondents have been routinely excluded from locating efforts with the exception of respondents who have died or, in a small number of cases, were judged to be extremely difficult. The permanent NLSY79 sample designated for interviewing during the 1979-1984 interview years consisted of all civilian and military youth who were interviewed in the base year and who were alive at the survey date.

In 1985, when interviewing of the full military sample ceased, the total NLSY79 sample size dropped from 12,686 to 11,607. Retained for interviewing in post-1984 surveys were 201 military respondents randomly selected from the entire military sample of 1,280; the remaining 1,079 military respondents were eliminated from the sample. The 201 military members who were retained included (1) 51 cases that would have been selected as part of a random sample of youth including the military and (2) 150 additional cases selected to provide a sufficient number of original military sample members to avoid overly large sampling variability for the military sample. Beginning in 1991, the 1,643 members of the economically disadvantaged, nonblack/non-Hispanic supplemental sample were no longer interviewed. Unless otherwise noted, eligible sample sizes reported in NLS publications include deceased and difficult-to-field respondents but exclude those respondents dropped from the sample. Additional information on numbers and characteristics of noninterviewed respondents can be found in the Reasons for Noninterview section.

NLSY79 respondents reside in each of the 50 States and the District of Columbia, U.S. territories, and other countries. Prior to fielding, respondents receive a short, informative advance letter reminding him or her of the upcoming interview and confirming the respondent's current address and phone number. As of the 2006 round, all main youth respondents are instructed to call and set up an appointment for their interview.

Field staff locating efforts begin when there is no contact from respondents. Using locator sheets, interviewers at the local level are responsible for contacting all respondents in their caseloads and for tapping additional local resources (post offices, departments of motor vehicles and vital statistics, and so forth) to locate those respondents who have moved. If an interviewer is unsuccessful in locating a respondent, the case is transferred to the field manager who undertakes additional locating strategies.

In the event that such local-level efforts fail, the case is forwarded to NORC's locating shop where the complete files on each respondent can be accessed and used for additional locating efforts. Respondents who cannot be located are only a small percentage of the total not interviewed in a given survey year. (For more information about noninterviews, refer to the Reasons for Noninterview section.)

In addition to its comprehensive locating efforts, NORC makes every effort to convert initial respondent refusals to completed interviews. Uncooperative respondents receive "refusal conversion letters" and a wide array of materials designed to encourage continued participation in the survey. Extensive locating methods and a strong conversion strategy, combined with close monitoring of response rates for each of the subsamples of the NLSY79, have resulted in relatively high retention rates for a longitudinal panel of this duration. 

In early rounds, telephone contact to complete the survey occurred under certain circumstances, such as 1987 when funding restrictions limited in-person interviews, or in any year, when the respondent resided in a remote area or field staff determined that phone contact was the preferred method of interviewing a respondent. Through the years, respondents have become more dispersed or expressed a preference for phone interviews. In response the number of telephone interviews increased greatly beginning in 2002 and is now the main mode of interviewing. The percent of surveys conducted by telephone for each survey year are shown in Table 1.

In rare cases, interviews are conducted in whole or in part with a proxy, a person other than the respondent (for example, four in 1991, two in 1992). A variable, entitled 'Interview Conducted with Proxy Respondent,' is present in the data to identify these interviews. In order to conduct such an interview, individual approval must be obtained by the NORC central office and the circumstances documented.

A Spanish version of the NLSY79 is prepared and NORC employs bilingual, Spanish-speaking interviewers. During the 2014 interview, for example, 93 respondents requested a Spanish version of the questionnaire.

The average length of a personal interview is approximately one hour. The 1987 telephone interviews were completed within about 40 minutes, while the administration of the child assessments added approximately 45 minutes to the total survey administration time for each child.

Until 1989, the NLSY79 was conducted using only paper-and-pencil interviews (PAPI). PAPI interviews were performed by interviewers filling in the relevant fields of large printed questionnaire booklets. While these booklets were inexpensive to produce, interviewers could make mistakes in following complicated skip patterns and filling in answers. Moreover, after all interviews were completed, additional office staff were needed to transcribe the information collected. Computer-assisted personal interviews (CAPI) were designed to eliminate many of these problems. With CAPI, interviewers take laptop computers into the field instead of questionnaire booklets. A computer program automatically selects the next question, prevents interviewers from entering illegal values, and warns interviewers about questionable answers. The computer also eliminates the need for data transcription except for specific items collected verbally and coded later.

While the majority of interviews in 1990 were collected using PAPI materials, a subset of one fourth of respondents was administered their survey using CAPI methods in order to test the viability and reliability of CAPI administration. Due to the success of these experiments, the NLSY79 interviews became fully CAPI administered beginning in 1993. Users interested in the results of these experiments should consult Olsen (1991).

Interview schedule and fielding periods

The original interview schedule, which called for yearly personal interviews with NLSY79 respondents, was retained from 1979 through 1986. In 1987, budget constraints dictated a limited phone interview rather than a personal interview. Personal interviews resumed with the 1988 round and continued yearly until 1994.  NLSY79 respondents have been interviewed in even-numbered years since 1994.

The initial NLSY79 interviews were conducted between late January and mid-August 1979. The next several interviews were fielded in the first six months of the year; more recently surveys have typically begun in winter and ended the following winter. Table 2 provides information on the fielding periods for NLSY79 respondents.

Note: There is no timing requirement that interviews take place on the same day/month from round to round. Thus, a respondent interviewed at the beginning of one field period and then interviewed at the latter end of the next field period would have more weeks between interviews than someone who was interviewed the same time both survey years. Also, some respondents, for various reasons, may miss multiple survey rounds before they are interviewed again. This means that the number of weeks since respondents' last interview can vary greatly. The LINT-DATE variables give the date last interviewed.

From 1979 until 1986, timing of the fielding period was designed to allow all respondents still in school to be interviewed before they left to take temporary summer jobs. Detailed information was collected for jobs held by respondents while they were in school. Since the youngest respondents in the survey were 23 years old in 1988, the shift in fielding periods after 1987 had a relatively small impact on information on jobs held while in school. An attempt was made during the initial survey years to keep the fielding period for an individual respondent approximately the same from year to year in order to assure that the time between interviews was approximately twelve months.

Researchers conducting analyses on topics where time periods are critical should carefully examine the reference period of the questions, the actual interview date, and the duration since the preceding interview.

• Sampling procedures
• Screening procedures
• Sampling process
• Multiple respondent households

Sampling procedures

In 1978 a list of housing units in selected areas of the United States was created for the first NLSY79 interview. Interviewers went to a random sample of these homes and performed a short interview, called the screener, which provided basic information on every resident of the household. Also using a random sample of Department of Defense records, the survey included members of the military.

Together these two processes provided information, such as name, age, sex, race, and address, on more than 155,000 people. This information was used to identify all individuals ages 14 to 21 as of December 31, 1978. Based on this screener information, each appropriately aged individual was assigned to one of the sample groups. Then, in 1979, interviewers asked individuals on this list to participate in the first NLSY79 interview. Any person who completed the first round interview is considered a member of the NLSY79 cohort.

Three independent probability samples compose the NLSY79. These samples are designed to represent the entire population of youth aged 14 to 21 as of December 31, 1978, residing in the United States on January 1, 1979. The three samples are:

1. a cross-sectional sample (6,111) designed to represent the noninstitutionalized civilian segment of young people living in the United States in 1979 and born January 1, 1957, through December 31, 1964
2. a set of supplemental samples (5,295) designed to oversample civilian Hispanic or Latino, black, and economically disadvantaged, nonblack/non-Hispanic youths born in the same time period
3. a military sample (1,280) designed to represent the population born January 1, 1957, through December 31, 1961, serving in the military as of September 30, 1978. The inclusion of the military sample allows comparative civilian-military analyses.

Beginning in 1986, additional information was collected about children born to female NLSY79 respondents. The child sample, when weighted, is representative of American children born to the population of women born in 1957 through 1964 and living in the United States in 1979. The sampling procedures used to select the civilian and military subsamples differed and are discussed separately below. For additional information on NLSY79 sampling procedures, see Frankel et al. (1983) and the Interviewer's Manual for the 1978 household screening (NORC 1978). Sampling issues related to the Children of the NLSY79 are discussed in Baker et al. (1993) and in the NLSY79 Child & Young Adult Data Users Guide.

Screening procedures

To find people of the correct age and ethnic composition, survey staff screened a large number of individuals in two separate procedures. First, household screening interviews were conducted to select the NLSY79 civilian cross-sectional and supplemental subsamples from the civilian population. Then, a second screening was done to identify the military sample. While the civilian screening made use of field interviewers going to selected households, the military sample was drawn from Department of Defense records.

NORC administered the civilian sample screening interview in approximately 75,000 dwellings and group quarters. These interviews occurred in 1,818 sample segments of 202 Primary Sampling Units (PSUs), which included most of the 50 States and the District of Columbia. The screening interview was designed to elicit information that would identify persons eligible for inclusion in the NLSY79 sample. The civilian screening interviews were completed within 91.2 percent of the cross-sectional and 91.9 percent of the supplemental occupied dwelling units selected for screening.

Cross-Sectional sample

Approximately 18,000 of the screening interviews were carried out among 918 sample segments in 102 Primary Sampling Units (PSUs), which were selected from the NORC Master Probability Sample of the United States.

Supplemental sample

A total of 57,000 screening interviews for the supplemental sample were carried out among 900 sample segments in a 100-PSU sample specifically designed to produce statistically efficient samples of Hispanics or Latinos, blacks, and economically disadvantaged, nonblack/non-Hispanics. The NLS sample design, which selected every eligible person connected to the household, generated a representative sample of siblings and spouses living in the same household and satisfying the age restrictions stated above. However, NLSY79 samples do not contain nationally representative samples of siblings and spouses of all ages and living arrangements. When the NLSY79 is used to study sibling pairs and married couples, care must be used in generalizing from the findings of such studies.

Procedures were also developed to establish "linkages" between dwellings and certain types of individuals who might be temporarily absent. As part of the initial screening for the civilian sample, household respondents were asked if there were any persons with primary family connections to the household who were away from the household at the time. Included in this group were college students, military personnel, and those in prisons or other institutions. Household screener respondents were also asked to name persons who might occasionally stay at the dwelling who did not have any other "usual place of residence." For each individual identified in this process, an attempt was made to determine whether the individual would be "linked" to some other household, such as college students living off campus in their own dwelling units. All individuals without other linkages were included in the household composition for purposes of sampling.

Military sample

Persons on active military duty as of September 30, 1978, were sampled from rosters provided by the Department of Defense. No formal screening interview was conducted.

Sampling process

Civilian sample

All civilian sample selection was accomplished through a multi-stage stratified area probability sample of dwelling units and group quarter units. A moderate degree of oversampling of dwelling units within sample listing segments was employed in order to increase the sample composition with respect to the targeted groups of the supplemental sample.

Base year samples of Hispanics or Latinos, blacks, and economically disadvantaged, nonblack/non-Hispanics were selected from individuals identified in both the 102 PSU cross-sectional sample and the 100 PSU special purpose sample. To the extent that individuals identified in the screening phase were obtained with different probabilities of selection (because of selective oversampling), the weighting of base year samples attempts to minimize these probability differences. Since the use of oversampling tends to decrease sample efficiency (that is, variance), attempts were made to minimize required oversampling.

Assignment of a youth to either the cross-sectional or supplemental sample was made using information collected during the household screening interviews and a set of coding instructions prepared by NORC. During the 1978 household screening interviews--from which the sample of NLSY79 respondents was drawn--information was collected on the sex, race, and ethnic origin of each household member and on the total income of the family unit during the past 12 months. A detailed set of coding procedures transformed these raw data into a combined racial/ethnic identifier and an economically disadvantaged qualifier. These criteria were used not only to assign a youth to one of the various subsamples, but also to specify the primary race or ethnicity variable, which provides the basis for weighting.

Other technical information on the sample assignment process can be found in the Household Screener and Interviewer's Manual (NORC 1978), which includes a copy of the screening instrument and detailed instructions to interviewers for administering the race, ethnic origin, and family income questions; and the Technical Sampling Report (Frankel et al. 1983), which describes the NLSY79 sample selection procedures for the civilian and military subsamples. Both of these documents are available at www.bls.gov/nls. Further information can be found:

1. in the 10/4/78 NORC memorandum, which provides the rules used to assign race and poverty status from responses to the screening questions;
2. a copy of the 1978 poverty income levels by family size and farm-nonfarm residence; and
3. the Race, Ethnicity, & Immigration section of this guide, which summarizes information in these documents as it relates to the assignment of "Hispanic," "Black," and "non-Hispanic, nonblack" origins used in the sample identification code variable (R01736.) and the race/ethnicity variable (R02147.).

Base year interviews with the three subsamples were conducted between January and mid-August 1979. Table 1 summarizes base year completion rates for each sample.

Cross-Sectional sample

Following the initial screening process, 6,812 individuals from the cross-sectional sample were designated to be interviewed in the base year; of those, 90 percent or 6,111 respondents were actually interviewed in 1979. The cross-sectional sample is designed to maximize the statistical efficiency of samples which are "cross-sectional" with respect to the rural population. Specifically, through the several stages of sample selection (counties, enumeration districts-block groups, sample listing units), probabilities of selection are based upon either total population or total housing units. Except for the economically disadvantaged supplemental sample, sampling of nonblack/non-Hispanic respondents was restricted to the 102 PSU National Sample.

Supplemental sample

After screening, 5,969 individuals from the supplemental sample were designated for base year interviews, and of these, 89 percent or 5,295 respondents were actually interviewed. Stratification specifically relevant for Hispanics or Latinos, non-Hispanic blacks, and economically disadvantaged, nonblack/non-Hispanics was used. Probability proportional to size procedures were based on size measures for these groups rather than for the general population, making it possible to more nearly equalize the distribution of the targeted groups among the various sampling units than would otherwise be the case.

Military sample

Of the 1,793 military youth selected for interviews, 1,280 or 72 percent were interviewed in 1979. Selection of the military sample was accomplished in two stages. In the first stage, a sample of approximately 200 "military units" was selected. These units were selected with probabilities proportional to the number of persons born in 1957 through 1961 and serving in the military unit as of September 30, 1978.

Within selected units, persons born in 1957 through 1961 were sampled with probabilities inversely proportional to the first-stage selection probability. Females were sampled at a rate approximately six times that of males in order to produce approximately 850 males and 450 females. Within each sex, the sample was stratified on the basis of branch of military service (Army, Navy, Air Force, and Marine Corps) and geographic location (Eastern U.S., Western U.S., Europe, Far East, other). Of those interviewed in 1979, 824 military respondents were male and 456 were female (see Table 2). The entire military sample was eligible for interview from 1979-84.

Child sample

The number of children assessed during a given child survey year is a function of the number of children born to interviewed NLSY79 mothers, the number of children living in the homes of those mothers, and, finally, the number of those children actually interviewed. Of the 5,842 NLSY79 females eligible for the first child interview in 1986, more than 2,900 mothers and 4,971 children were interviewed. From this sample of eligible children, assessment data were collected for 4,786.

Multiple respondent households

Respondents interviewed in 1979 originated from 8,770 unique households; 2,862 households included more than one NLSY79 respondent. The most common relationships between respondents living in multiple respondent households at the time the survey began were those of sibling or spouse (see Table 3). During the 1979 survey, 5,863 respondents were members of a household containing multiple interviewed siblings. More than 330 respondents were members of a household in which their spouse was also interviewed.