National Longitudinal Surveys
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.
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 197984 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.