Sample Design

Sample Design

Sibling and Cousin Samples

When the sample selection for NLSY79 was made, all individuals living in the selected households who were between the ages of 14 and 21 on December 31, 1978, were selected for sample inclusion. In many instances, siblings were included in the original sample. This has methodological implications for those who are concerned about the lack of complete independence between all of the NLSY79 cases. There are many main Youth sisters who are respondents in the NLSY79 sample. The Sample Design & Screening Process section of the NLSY79 User's Guide details this information, so it is not explained extensively here. 

The focus in this section is on the children who have been born to the female respondents in this kinship sample. From the child's perspective, children of sisters are cousins to each other. Over the course of the survey years, more than 3,000 children in the sample have been identified as having an aunt in the NLSY79 main youth sample. Most of these children have one aunt, but smaller numbers have multiple aunts. While the number of children who are cousins is considerable, the precise numbers available for a particular research project are contingent on the objectives of the research. For example, will the researcher limit the sample to children or women interviewed in only the current survey year or will the researcher include mothers or children interviewed in one or more of the earlier survey rounds?

More typically, researchers utilize the large number of child sibling sample cases that have been born to the female respondents. As seen in Table 5, most of the women have had more than one child, including a rather large sample of women who have had three or more children, as they approach the end of their childbearing years. 

Table 5. NLSY79 Women by Number of Children and Race/Ethnicity

    Number of Households
Type of Household (Female) Hispanic Black White Total
Females with no children 156 283 901 1340
Mothers with 1 or more child 846 1278 2819 4943
  Mothers with 1 child 148 279 751 1178
  Mothers with 2 children 309 457 1204 1970
  Mothers with 3 children 222 315 593 1130
  Mothers with 4 or more children 167 227 271 665
 Total   1002 1561 3720 6283

NLSY79 female respondents who are sisters, as well as children born to those sisters, can be readily identified. NLSY79 female respondents who are sisters and who were resident in the same household when the original main youth sample was selected can be identified by variables on the child file called SISTID1- SISTID3 (C00010.00-C00012.00). Children born to a particular respondent all share the same stem as the ID of their mother, with an additional two-digit identifier (01, 02 etc.) that typically (although not in all cases) clarifies their sibling placement.

In addition to multiple births, there are many family units where two or more children are widely spaced in age, thus enhancing the possibility of exploring the impact of childbearing on children that have been born to the same mother at different maternal life cycle stages. Larger sample sizes can be generated by incorporating women who were not interviewed in the current survey year but who had been interviewed in earlier survey rounds.

Depending on research topic, some users may be interested in young adults with siblings in the young adult sample. Sample sizes for this subset are shown in Table 6. Most of these siblings have also been interviewed in past rounds, providing researchers with ample data to carry out within-family analyses. 

Table 6.  Siblings of Young Adults Interviewed Who Were Also Interviewed in 2020

  Young Adults Interviewed in 2020*
Siblings If Yes, Number of Siblings
No Yes One Two Three+
Any Siblings? 1,468 2,886 1,752 771 363
* N = 4,354 young adults interviewed