Chapter 2: Sample Design and Attrition

2.1 Sample Design

The original NLS of Young Women sample was designed to represent the civilian noninstitutionalized population of the United States ages 14-24 as of December 31, 1967, at the time of the initial survey. The cohort is represented by a multi-stage probability sample drawn by the 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 primary sampling unit consists of Standard Metropolitan Statistical Areas (SMSAs), counties (or parishes in some states), parts of counties, and independent cities. A total of 235 sample areas, comprising 485 counties and independent cities, were chosen to represent every state and the District of Columbia. From the sample areas, 235 strata were created of one or more PSUs that were relatively homogeneous according to socioeconomic characteristics. 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 the addresses for the sample frame came from the 1960 Census, respondents are covered by Title 13 confidentiality restrictions. Variables linked to geographic residence, including county and state, are available for use at Census Data Centers (see www.ces.census.gov for more information).

Return to top

2.2 Screening Process

As dictated by the above requirements, the initial sample of about 42,000 housing units for all four NLS Original Cohorts was selected and screening interviews took place in March and April of 1966. Of this number, about 7,500 units were found to be either vacant, occupied by persons whose usual residence was elsewhere, changed from residential use, or demolished. On the other hand, about 900 additional units were found created within existing living space or changed from what had been nonresidential space. A total of 35,360 housing units were available for interview, from which usable information was collected for 34,662 households for a completion rate of 98.0 percent.

The original plan called for using the initial screening to select all four NLS Original Cohorts. However, after the sample members for the Older Men were chosen, the sample was rescreened in September 1966 before the initial interview of the Young Men. This decision was made because a seven-month delay between the screening and first interview seemed inordinate due to the mobility of Young Men in their late teens and early twenties. To increase efficiency, it was decided to stratify the sample for the rescreening by the presence or absence of a 14- to 24-year-old male in the household. The probability was high that a household that contained a 14- to 24-year-old in March would also have such a member in September. However, to insure that the sample also represented persons who had moved into sample households in the intervening period, a sample of addresses that previously had no 14- to 24-year-old males was also included in the rescreening operation. Since a telephone number had been recorded for most households at the time of the initial screening interview, every attempt was made to complete the short screening interview by telephone. The sample of households from the initial screening, supplemented with information from the rescreening, was subsequently used to obtain the two samples of women ages 30-44 and 14-24 for the Mature Women and Young Women cohorts (Parnes et al. 1970; Shea et al. 1971).

Return to top

2.3  Sampling Process

Following the initial household interview and rescreening operation, 5,533 women ages 14-24 as of December 31, 1967, were designated to be interviewed for the Young Women cohort. The sample was designed to provide approximately 5,000 respondents--about 1,500 nonwhites and 3,500 whites. The women were sampled differentially within four strata:  whites in predominantly white enumeration districts (EDs), non-whites in predominantly non-white EDs, whites in predominantly non-white EDs, and non-whites in predominantly white EDs. An enumeration district is a geographical area considered to be an appropriate size for an interviewer to complete all necessary interviews within a prescribed time frame. To provide separate reliable statistics for black respondents, the sample design called for oversampling of blacks at twice the expected rate in the total population. The sampling rate of households in predominantly non-white EDs was between three and four times that for households in predominantly white EDs in order to meet this survey requirement. During the first survey in 1968, 5,159 (93.2 percent) of the designated women were interviewed.

Return to top

2.4 Interview Schedule & Fielding Periods

In the initial survey plan, respondents from each of the four Original Cohorts were to be interviewed yearly over a five-year period. However, due to cost considerations, it was decided after the second survey of the Older Men to survey the two older groups (Older Men and Mature Women) biennially rather than annually. Due to their greater mobility, the Young Women and Young Men were interviewed annually. A decision was made at the end of the first five-year period to continue the interviews for another five years because of the usefulness of these data and the relatively small sample attrition. At this point, the interviewing pattern changed from a yearly personal interview to a 2-2-1 schedule; each respondent was contacted by phone approximately every two years, then again in person one year after the second phone interview. The 2-2-1 schedule was continued through 1988, when the decision was made to conduct a personal interview every other year. However, the implementation of the biennial schedule was interrupted by the 1990 decennial Census. Thus, the scheduled 1990 Young Women survey was pushed back to 1991. Table 2.4.1 depicts the years in which the cohort was surveyed along with the fielding period, the percent of the cohort interviewed, and the type of interview utilized in each survey year. Users should note that, in years during which the survey was conducted in person, some interviews were administered by telephone when necessary.

Table 2.4.1  Sample Sizes, Retention Rates, and Fielding Periods