Handbook of Methods National Longitudinal Surveys Data sources
National Longitudinal Surveys: Data sources
The National Longitudinal Survey (NLS) cohorts each consist of a sample of individuals who were born in a particular set of years and who were living in the United States at the time of the first survey. For example, the NLSY97 survey consists of individuals born in the years 1980–84 who were living in the United States when surveyed for the first time in 1997. The same sample of individuals is interviewed every year or every other year, generating a longitudinal record for each sample member. Collection is organized into rounds, and each round is conducted over many months. The NLS collects information from each sample member about their experiences since the date of their last interview. Rounds have been initiated every year or every other year during the time each cohort has been active.
Survey collection
NLS interviews have been conducted either in-person or by telephone; an online special supplement was recently fielded in the NLSY97. Personal visits are typically made to each respondent’s home during the initial interview and for many rounds thereafter, but each survey has switched to telephone as the primary mode as the respondents got older, supported by in-person visits when necessary. Interviews are conducted by U.S. Bureau of Labor Statistics (BLS) contractors, who use computer-assisted personal interviewing (CAPI) or computer-assisted telephone interviewing (CATI) to minimize respondent burden and process collected data efficiently. A typical interview takes slightly over an hour. Computer-assisted recorded interviewing (CARI) is used for data quality assurance, and a small number (less than 2 percent) of completed interviews are validated every round. The cases to be reinterviewed are selected purposefully, based on data assessments by survey management and the presence of missing audio on CARI files.
Throughout the collection process, BLS contractors make extensive efforts to maintain high standards for accuracy and professionalism. Interviewers are carefully trained, with particular emphasis placed on resolving sensitive issues that may have appeared in previous rounds. To begin interviewing, they must complete a comprehensive and robust online training covering the questionnaire and its administration, data quality, study protocols and procedures, and respondent confidentiality. During the round, interviewers must attend training calls with their field managers, pass certification tests, participate in regular communications to reinforce proper procedures, get tips for improving field work, and receive updates from the central office. Most of the interviewers have extensive experience in the field from having participated in earlier rounds of the NLS and other surveys.
Additional information about the NLSY79 and NLSY97 interview methods can be found online.
Questionnaire content
During the process of screening each cohort’s sample and in the first round of collection, background variables are collected, such as birthdates, race and ethnicity, and sex, as well as a roster of the resident household. The roster is updated in subsequent rounds as the sample member’s living situation changes, and questionnaires are carefully designed to capture the most relevant factors affecting and affected by the respondent’s evolving work life, among a myriad of other topics. These data include information on the following topics:
- Education, training, and achievement scores
- Employment, jobs, and job search
- Household, geography, and contextual variables
- Family background
- Dating, marriage, fertility, and children
- Income, assets and program participation
- Health conditions and practices
- Attitudes, expectations, and noncognitive tests
- Crime, substance use, and interactions with the justice system
The development of each 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. This development generally begins at least 2 years prior to the fielding. Each of the ongoing surveys has its own design team made up of BLS staff, NLS 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. Questions tend to focus on a cohort’s current stage of life. For example, consider the NLSY79 cohort, which has been interviewed regularly for over 40 years. When sample members were younger, special topics included family background, knowledge of the world of work, educational and occupational aspirations, and expectations. As the respondents aged, additional questions were included on many topics, such as various health behaviors and conditions, job search and later retirement, and migration. The NLSY97 has similarly seen changes in the types of questions asked of respondents as the cohort has aged since the survey’s inception. Changes from the NLSY79 to the NLSY97 include 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.
Additional collection
In addition to the data collected via the questionnaires described above, the NLS acquires data through many additional means, including the collection of supplemental surveys, the administration of diagnostic tests, and the incorporation of administrative records. Some primary examples of previous efforts to enrich the main survey in this way include a survey of the parents of NLSY97 youth, the administration of the Armed Services Vocational Aptitude Battery (ASVAB) to NLSY79 and NLSY97 youth, and the collection of high school transcripts for NLSY79 and NLSY97 youth. Additional information about these collections can be found at the following locations:
ASVAB Administration:
High School Transcripts:
Data processing
After data for each round are collected, they undergo an extensive set of reviews and editing procedures to ensure that they consistently adhere to common formats and concepts and do not contain errors. Many responses such as those provided in open formats are recoded to comport with common classification systems such as the North American Industry Classification System (NAICS) and the Standard Occupational Classification (SOC) System. In addition, NLS contractors create variables to enable use of the data by combining responses across rounds or different parts of the survey. For example, they create event-history arrays to facilitate analyses of employment, schooling, etc. Combining these efforts, several different types of variables are present in the NLS data:
- Direct (or raw) responses from a questionnaire or other survey instrument
- Symbols and roster items, which are used to guide the interview
- Created variables based on responses to more than one data item. These items are edited for consistency where necessary
- Created event-history arrays for employment, schooling, etc.
- Created variables from data provided from outside sources such as high school transcripts
Last Modified Date: May 28, 2025
United States Department of Labor
