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Chapter 7.

National Longitudinal Surveys

IN THIS CHAPTER

Background .............................................................. 1

Sampling ................................................................... 1

Questionnaire Design ............................................. 2

Collection Methods ................................................ 3

Estimation ................................................................. 4

Uses ........................................................................... 4

Presentation and Availability ................................. 5

Technical References .............................................. 5

Background

The National Longitudinal Surveys (NLS) are a set of surveys designed to gather information at multiple points in

time on the labor market experiences (for example, employment histories and job characteristics) of six groups of the U. S.

population. For more than three decades, NLS data have

served as an important tool for economists, sociologists,

government analysts, and other researchers who are interested in the study of employment behavior and human capital investments, among other topics.

The NLS were begun in the mid-1960s with the drawing of

four samples: Young men were 14 to 24 years old as of December 31, 1965; young women were 14 to 24 years old as of

December 31, 1967; older men were 45 to 59 years old as of

December 31, 1965; and mature women were 30 to 44 years

old as of December 31, 1966. Each sample originally had about

5,000 individuals, with an overrepresentation of blacks. In

the early 1980s, the surveys of young men and older men

were discontinued. (However, there was a followup of the

older men or their widows or other family members in 1990.)

The two women’s surveys continue and are currently collected on a biennial cycle.

In 1979, a new cohort was begun with a sample of more

than 12,000 young men and women who were 14 to 21 years

old as of December 31, 1978. This sample included

oversamples of blacks, Hispanics, economically disadvantaged nonblacks and non-Hispanics, and youths in the military. The military oversample was discontinued after the 1984

survey, and the economically disadvantaged nonblack and

non-Hispanic oversample was discontinued in 1990. This

survey is called the Youth 1979 data set, or NLSY79; its cohort was interviewed annually from 1979 to 1994 and on a

biennial basis thereafter.

In 1997, data collection began for the sixth NLS cohort.

The National Longitudinal Survey of Youth 1997 (NLSY97)

documents the transition from school to work for a group of

approximately 9,000 young people aged 12 to 16 as of December 31, 1996. This cohort is interviewed on an annual

basis and includes oversamples of black and Hispanic

youths.

Besides collecting information about labor market experiences, the surveys have gathered information regularly about

a range of factors potentially affecting labor market attachment, including investments in education and training, local

labor market conditions, parental influence, marital and fertility histories, income and assets, and participation in government assistance programs.

With the advent of the NLSY79 in the late 1970s, the content of the surveys expanded to reflect the interests of other

government agencies besides the U.S. Department of Labor.

For example, support from the U.S. Department of Defense

made possible the administration of the Armed Services Vocational Aptitude Battery (ASVAB) to youths in the NLSY79

in 1980 and, later, to the NLSY97 cohort. The National Institute of Child Health and Human Development (NICHD) has

provided funds for assessments and surveys of the children

of female respondents in the NLSY79 and the development

of the fertility and childcare components of the NLSY79. The

1989 National Longitudinal Survey of Mature Women pension-matching project received funding from other agencies

in the Department of Labor, as well as from the Social Security Administration and the National Institute on Aging. The

National School-to-Work Office (which is jointly funded by

the U.S. Departments of Education and Labor) both sponsored the 1996 and 2000 school surveys of the NLSY97 and

provided funding for the collection of high school transcript

data for the cohort. In addition, sections of the NLSY97 are

funded by the U.S. Department of Justice’s Office of Juvenile Justice and Delinquency Prevention and by NICHD.

Sampling

Each of the four original NLS samples was designed to represent the civilian noninstitutionalized population of the United
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States at the time of the initial survey. Each age-sex cohort is

represented by a multistage probability sample drawn by the

U.S. Census Bureau from 1,900 primary sampling units (PSUs)

that had originally been selected from the Nation’s counties

and cities for the experimental Monthly Labor Survey conducted between early 1964 and late 1966. A PSU consists of

Standard Metropolitan Statistical Areas (SMSAs), counties

(or parishes in Louisiana), parts of counties (parishes), and

independent cities. A total of 235 sample areas comprising

485 counties and independent cities was chosen to represent every State and the District of Columbia. From the sample

areas, 235 strata consisting of one or more PSUs that were

relatively homogeneous according to socioeconomic characteristics were created. Within each stratum, a single PSU

was selected to represent the stratum. Finally, within each

PSU, a probability sample of housing units was selected to

represent the civilian noninstitutionalized population.

Because one of the survey requirements was to provide

separate reliable statistics for blacks, households in predominantly black enumeration districts (EDs) were selected at a

rate between 3 and 4 times that for the households in predominantly white EDs. The sample was designed to provide

approximately 5,000 interviews for each of the four cohorts—

about 1,500 blacks and 3,500 whites.

For the NLSY79 cohort, the following three independent

probability samples, which were designed to represent the

entire population of youths born between 1957 and 1964 and

living in the United States in 1978, were drawn: (1) A crosssectional sample designed to be representative of the

noninstitutionalized civilian segment of young people aged

14 to 21 years as of December 31, 1978; (2) a supplemental

sample designed to overrepresent civilian Hispanic, black,

and economically disadvantaged non-Hispanic, nonblack

youths; and (3) a military sample designed to represent the

population aged 17 to 21 as of December 31, 1978, and serving in the military as of September 30, 1978.

All sample selection was done through a multistage stratified area probability sample of dwelling units and groupquarters units, except for individuals on active military duty.

A screening interview was administered in approximately

75,000 dwellings and group quarters distributed among 1,818

sample segments in 202 PSUs (inclusive of most of the 50

States and the District of Columbia). As part of this screening interview, information was obtained that would allow the

identification of persons eligible for membership in the

sample.

Members on active military duty as of September 30, 1978,

were sampled from rosters provided by the Department of

Defense. Sample selection was accomplished in two stages.

In the first stage, a sample of approximately 200 “military

units” was selected, with probabilities proportional to the

number of persons aged 17 to 21 years within the unit. Within

selected units, persons aged 17 to 21 years were subsampled

with probabilities inversely proportional to the first-stage

selection probability. Females were oversampled at a rate

approximately 6 times that of males, in order to produce approximately equal numbers of males and females. Within each

sex, the sample was stratified on the basis of military service

(Army, Navy, Air Force, and Marine Corps) and geographic

location.

The NLSY97 cohort consists of two independently selected, stratified, multistage area probability samples designed

to represent noninstitutionalized youths born between 1980

and 1984 and living in the United States in 1997: A crosssectional sample and an oversample of black and Hispanic

youths. For each probability sample, 100 PSUs were selected

to represent all 50 States and the District of Columbia. For

the cross-sectional sample, the probability of selection for

each PSU was proportional to the 1990 census count of its

housing units. For the supplemental sample, probabilities of

selection for PSUs and segments were based on 1990 census

counts of blacks and Hispanics aged 17 years and younger.

In addition, areas that contain high percentages of black and

Hispanic residents were oversampled. Only eligible black

and Hispanic youths were screened into the NLSY97 sample

from the supplemental areas.

Each of the four original cohorts was interviewed initially

between 1966 and 1968. Respondents for the NLSY79 were

first interviewed in 1979, and interviewing for the NLSY97

began in 1997. About 90 percent of the individuals designated for interviewing responded to each of the first-year

interviews: 5,020 (91 percent) of the older men and 5,225 (92

percent) of the young men were interviewed in 1966; 5,083

(94 percent) of the mature women were interviewed in 1967;

5,159 (93 percent) of the designated young women were interviewed in 1968; 12,686 (90 percent) of the NLSY79 were

interviewed in 1979; and, finally, 8,984 (92 percent) of the

NLSY97 cohort were interviewed in 1997. Completion rates

for the initial and latest survey years of each of the cohorts

are summarized in table 1.

Questionnaire Design

The development of a questionnaire involves a review of

earlier questions, the analysis of field notes from the previous round, and the identification of new topics and questions for inclusion in the current survey. The development of

each survey instrument generally is begun at least 2 years

prior to the fielding. Each of the ongoing surveys has its

own design team made up of Bureau of Labor Statistics staff,

NLS survey contractors, and outside experts. Advice from

the NLS Technical Review Committee and other Government

agencies is often sought regarding survey questionnaire initiatives and other survey-related issues.

The central focus of each cohort’s survey is, to some

extent, determined by the particular stage of labor market

attachment that each of these six unique age-sex groups is

experiencing at the time of the interview. Each survey instrument is organized around core sets of questions on the following topics: Employment, education, training, marital status, fertility, participation in government assistance programs,

income, and assets.
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Table 1. Completion rates by NLS cohort for the initial and latest survey years

Older men ................................................ 5,518 5,020 91 1966 2,092 42 1990

Mature women ......................................... 5,393 5,083 94 1967 2,318 46 2001

Young men ............................................... 5,713 5,225 92 1966 3,398 65 1981

Young women ........................................... 5,533 5,159 93 1968 2,806 54 2001

Youth 1979 ............................................... 14,574 12,686 87 1979 8,033 81 2000

Cross-sectional sample ........................... 6,812 6,111 90 4,949 81

Supplemental sample ......................... 5,969 5,295 89 2,921 80

Military sample .................................... 1,793 1,280 72 163 81

Youth 1997 ............................................... 9,806 8,984 92 1997 7,883 88 2001

Cross-sectional sample ..................... 7,327 6,748 92 5,919 88

Supplemental sample ......................... 2,479 2,236 90 1,964 88

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In 1990, interviews also were conducted with 2,206 widows or

other family members of deceased respondents.

2After the majority of the military sample was dropped in 1985

Each cohort also is asked questions that are focused on

its stage in the life cycle. For example, the surveys of older

men have focused on plans for their future—specifically,

retirement, pension plan participation, and health. Special

topics for the mature women’s cohort have included questions on household and volunteer activities, childcare, care

of parents, plans for retirement, and pension plan participation. The surveys of both the young men’s and young

women’s cohorts have focused on educational goals, high

school and college experiences, characteristics of their high

schools, and future job plans. The young women’s cohort

is ongoing, and, as the women are aging, the focus is shifting to retirement issues and transfers of time and money to

and from their parents and their children.

The NLSY79 cohort has been interviewed periodically for

over 20 years. When sample members were younger, special

topics included their family background, knowledge of the

world of work, educational and occupational aspirations, and

expectations. As the respondents aged, special groups of

questions were asked about pre- and postnatal health behaviors, job search, migration, and drug and alcohol use,

among other topics. The changing life stage of the NLSY79

cohort prompted the NLS program to hold an NLSY79 Redesign Conference in 1998. The goal was to evaluate current

questions in key areas of the survey, identify areas for improvement, and provide direction for future rounds as the

NLSY79 passes into its next life stage. The NLS program

commissioned papers by experts in key subject areas to provide this information and received many useful recommendations therefrom.

Eight development teams, each composed of recognized

experts in critical content areas, contributed to the design of

the initial NLSY97 survey. Lessons learned from the NLSY79

and other NLS cohorts were incorporated into the design of

the NLSY97 survey instrument. The NLSY97 design team

meets quarterly to discuss changes that might improve each

round’s questionnaire to capture youths’ transitions from

school to work and into adulthood. Among the many innovations in the NLSY97 are the collection of information on

the work experience of the very young in freelance jobs, the

gathering of data on delinquent and criminal behaviors, and

the accumulation of extensive information on high school

and college experiences.

Collection Methods

Respondents selected for interviewing each year, with the

exceptions noted next, are those who had participated in the

initial-year interviews and who were alive on the date of the

interview.

For the original cohorts, subsequent to the first-year interview, those respondents who had refused to be interviewed

were dropped from the sample. Beginning with the third interview year, respondents who had not been interviewed for

any reason for 2 consecutive years also were eliminated from

the sample. However, this noninterview exclusion was not

applied to those members of the young men’s cohort who

were subsequently inducted into the Armed Forces. No interviews were attempted with that group while its members

were on active military duty. They were, however, retained in

the sample and interviewed as soon as they left active military service. Beginning in the mid-1980s, the procedures for

selecting respondents for interviewing were modified, and

refusals and those not interviewed for 2 survey years were

not dropped.

NLS cohort

Designated

for

 interviewing

Number and percent interviewed in

initial survey year

Number and percent interviewed in

last or latest survey year

Number Percent Year Number Percent Year

and the economically disadvantaged nonblack, non-Hispanic oversamples were eliminated in 1991, the sample was left with 9,964

respondents eligible for interview.

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In the NLSY79 survey, attempts are made to reach all individuals within the active samples. No respondents have been

routinely excluded from locator efforts, with the exception of

respondents who have died. The permanent NLSY79 sample

designated for interviewing during the 1979–84 interview

years consisted of all civilian and military youths who were

interviewed in the base year and who were alive on 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 were the original 11,406

civilian respondents, as well as 201 military respondents.

After the 1990 survey, interviews with the economically disadvantaged nonblack, non-Hispanic oversample were discontinued, reducing the NLSY79 sample size to 9,964.

In the new youth cohort (the NLSY97), surveyors attempt

to interview the full sample of 8,984 respondents in each

round, regardless of whether they have been interviewed in

previous rounds.

Although personal interviews have been the method used

during most survey years, at times telephone interviews also

were conducted. In addition, interviews by mail were conducted for the 1968 older men and mature women surveys.

Telephone contact may occur in cases where the respondent

resides in a remote area or the field staff determines that the

respondent prefers to be interviewed by telephone.

Originally, the NLS interviews were conducted with paper

and pencil. Interviewers filled in the relevant fields in long

questionnaires, and, as a result, the interviewing process

was slow and burdensome. With the advent of newer, faster

computers, the NLS switched to computer-assisted personal

interviews (CAPI), for which interviewers take laptop computers instead of questionnaire booklets into the field. A

computer program automatically selects the next question,

prevents interviewers from entering invalid values, and warns

interviewers about implausible answers, all with an eye toward increasing the quality of the data collected. The first

cohort to begin using CAPI was the NLSY79 in 1993. The

women’s surveys were switched over to CAPI in 1995. The

newest NLS cohort, the NLSY97, has used only CAPI. In

addition, it contains an audio computer-assisted self-interview (ACASI), in order to obtain potentially sensitive information from respondents, such as information on their drug

and alcohol use and criminal behavior. The respondent is

able to listen to the questions with earphones or read the

questions on the screen, or both, and then enter his or her

response.

Estimation

The NLS surveys are based upon stratified multistage random samples, with oversamples of blacks in all cohorts,

oversamples of Hispanics in the NLSY79 and NLSY97, and

additional oversamples of disadvantaged nonblack non-Hispanics and youths in the military in the NLSY79. Data from

each interview year include a weight specific to that year.

When this weight is applied, the number of sample cases is

translated into the number of persons in the population that

those observations represent.

The assignment of individual respondent weights involves at least three stages. The first stage involves the

reciprocal of the probability of selection at the baseline interview. Specifically, this probability of selection is a function

of the probability of selection associated with the household in which the respondent was located, as well as the

subsampling (if any) applied to individuals identified in

screening. The second stage of weighting adjusts for differential response (cooperation) rates in the screening phase.

Differential cooperation rates are computed (and adjusted)

on the basis of geographic location and group membership,

as well as by group subclassification. The third stage of

weighting attempts to adjust for certain types of random

variation associated with sampling, as well as sample

“undercoverage.” The estimated ratios are used to conform

the sample to independently derived population totals.

Subsequent to the initial interview of each cohort, reductions in sample size have occurred due to noninterviews (the

failure, for one reason or another, of the person to be interviewed). In order to compensate for these losses, the sampling weights of the individuals who were interviewed had

to be revised. A revised weight for each respondent was

calculated for each interview year, using the method just

described.

In the event that one wishes to tabulate characteristics of

the sample for a single interview year in order to describe the

population being represented, it is necessary to weight the

observations by using the weights provided. For example, to

compute the average hours worked in 1987 by individuals in

the NLSY79 (persons born in 1957–1964 and living in the

United States in 1978), one simply weights the average hours

worked by the 1987 sample weight. The weights are correct

when used in this way.

Often, users confine their analyses to subsamples for

which respondents provide valid answers to certain questions. Weighted means here will represent, not the entire

population, but rather those persons in the population who

would have given a valid response to the specified questions. Nonresponse to any item because of refusals or invalid skips is generally quite small, so the degree to which

the weights are incorrect also is probably quite small. In

these instances, although the population estimates may be

moderately in error, the population distributions (including

means, medians, and proportions) are reasonably accurate.

Exceptions to this assumption might occur for data items

that have relatively high nonresponse rates, such as family

income.

Uses

NLS data are important tools for economists, sociologists,

psychologists, and other researchers in the study of labor

supply, earnings and income distribution, job search and

separation, training, and other human capital investments.

In addition, these data are used to study the effect of government policies and programs on labor market behaviors.
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Several comprehensive reviews of NLS research (Bielby,

Hawley, and Bils, 1979; Daymont and Andrisani, 1983) and

the NLS Annotated Bibliography (which provides citations

and abstracts of thousands of publications, dissertations,

and other research papers that have used NLS data over the

years) summarize much of the work that has been generated

by the NLS since the mid-1960s. A recent article in the Journal of Economic Perspectives focuses on significant areas

and corresponding research done with the NLSY79 (Pergamit

and others, 2001). The continued relevance of the NLS for

policymakers at the Federal, State, and local levels, as well as

for the research community, is summarized in The Future of

the NLS: A Report from the NSF Conference on the Future

of the NLS and the NLS Technical Review Committee (Center for Human Resource Research, 1989). A summary of some

uses of the NLS made by the Federal Government can be

found in How the Federal Government Uses Data from the

National Longitudinal Surveys (Pergamit, 1991).

The broad range of core NLS data, coupled with the extensive expansion of the youth surveys, the ongoing longitudinal nature of the data, and the replication of cohorts

across time, helps to make the NLS a rich and yet-to-be fully

exploited source of data for the continued study of such

issues as labor market behavior, life-cycle changes, the family, the aging process, retirement decisions, and geographic

mobility, as well as a host of other topics and methodologies.

Presentation and Availability

Extensive information about the NLS can be found on the

NLS Web site, http://www.bls.gov/nls, which houses BLS

press releases on recent findings about employment from

the NLSY79 and NLSY97 surveys and provides links to

Monthly Labor Review articles that use NLS data, the NLS

Discussion Paper series, and the NLS Annotated Bibliography. The site also provides links to the extensive NLS documentation available, such as the NLS Handbook and cohortspecific NLS User’s Guides.

One of the great strengths of the NLS program is the ease

with which its data can be accessed. NLS data are on cohortspecific compact discs, complete with user-friendly searchand-retrieval software. Check the NLS Web site for information on how to order NLS data files. In addition, data are now

available for downloading from the NLS Web site.

Bielby, William T., Clifford B. Hawley, and David Bils. “Research Uses of the National Longitudinal Surveys,” R&D

Monograph 62 (U.S. Department of Labor, Employment

and Training Administration, 1979).

Bureau of Labor Statistics. NLS Handbook (Bureau of Labor Statistics, 2003).

Center for Human Resource Research. The Future of the

NLS: A Report from the NSF Conference on the Future of

the NLS and the NLS Technical Review Committee (Columbus, The Ohio State University, 1989).

__________. NLS Cohort-Specific User’s Guides (Columbus, The Ohio State University, 2002).

Daymont, Thomas N. and Paul J. Andrisani. “The Research

Uses of the National Longitudinal Surveys: An Update,”

Review of Public Data Use (U.S. Department of Commerce, 1983).

Pergamit, Michael. How the Federal Government Uses Data

from the National Longitudinal Surveys, Report NLS 92-1

(Bureau of Labor Statistics, 1991).

Pergamit, Michael R., Charles R. Pierret, Donna S. Rothstein,

and Jonathan R. Veum. “Data Watch: The National Longitudinal Surveys,” Journal of Economic Perspectives, vol.

15, no. 1, spring 2001, pp. 239–53.

Technical References