Sample Design

Sample Design

The NLSY79 Child sample is comprised of all children born to NLSY79 mothers. Starting in 1986, the children of the NLSY79 mothers have been interviewed and assessed biennially to follow their cognitive, physical, and socio-emotional development. Starting in 1994, children who have reached the age of 15 by the end of the survey year are no longer assessed but instead complete personal interviews similar to those given to their mothers during late adolescence and into adulthood. Upon reaching age 15, the NLSY79 children become part of the NLSY79 Young Adult sample.

As of 2012, a total of 11,512 children have been identified as having been born to the original 6,283 NLSY79 female respondents, mostly during the years that they have been interviewed.  A modest number of children were born prior to 1979, the first main Youth interview round. Obviously, an unknown number of additional children have been born to women who have left the survey, subsequent to their attrition from the sample.

The number of children assessed during a given child survey year is a function of the number of children born to interviewed NLSY79 mothers, the number of children living in the homes of those mothers, and, finally, the number of those children actually interviewed. Of the 5,842 NLSY79 females eligible for the first child interview in 1986, more than 2,900 mothers and 4,971 children were interviewed.  From this sample of eligible children, assessment data were collected for 4,786. As of the most recent survey, a total of 11,512 children have been identified as having been born to the original 6,283 NLSY79 female respondents, Of these, 515 children under age 15 (as of 12/31/2012) were assessed in 2012 and 5,808 were interviewed as young adults. Details on the sizes and eligibility criteria of the samples are discussed below.

 

Important Information

Sampling weights. Appropriate weights are available in each year to adjust the unweighted sample cases for the minority oversamples and year-to-year sample attrition. A detailed discussion of the sampling weights can be found in the Sample Weights section.

Sample Sizes: Who Was Interviewed in the Current Survey Round?

In 2012, a total of 6,323 children, including young adults, were interviewed (see Table 1). Of these, 515 were interviewed as children (under age 15 as of 12/31/2012) and 5,808 were interviewed as young adults. In the context of the child interviews, "interviewed" for children under age 15 means that some child-specific assessment information was obtained from either the mother or child in that survey year.  From the perspective of the Young Adult sample, a completion is defined as a case in which at least a part of the Young Adult interview was completed. 

Table 1. NLSY79 Mother & Child Samples: 1979-2012 Surveys

  1979 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012
Female Respondents                              
  Interviewed 6283 5418 5312 4510 4535 4480 4361 4299 4113 3955 3984 3916 3975 3896 3777
Mothers                              
  # Mothers Interviewed -- 2922 3346 3088 3325 3464 3489 3533 3425 3315 3365 3311 3356 3280 3192
Children
                             
 Born1 -- 5255 6543 6427 7255 7862 8125 8395 8323 8100 8267 8131 8266 8099 7892
 Interviewed2 -- 4971 6266 5803 6509 7089 7103 70673 6417 74674 75385 78166 76607 69978 63239
  Under Age 15           6109 5431 4924 3392 3229 2514 1972 1354 895 515
  Age 15 and over           980 1672 2143 3025 4238 5024 5844 6306 6102 5808
                                 
Note: Sample sizes for all child survey years exclude the 441 female members of the military subsample dropped from interviewing in 1985 and the children born to these women. In addition, sample sizes for 1990 and later surveys exclude female members of the civilian economically disadvantaged, non-black/non-Hispanic subsample, whose children were not eligible for assessment or for interview as young adults. (Women in this oversample were interviewed in 1990, but their children were not included in that year due to budget constraints and in anticipation of the dropping of the sample the next round.) The exclusion of this sample after 1988 accounts for much of the drop in sample size between 1988 and 1990. Young adults age 21 and older were not fielded in 1998 but were returned to the eligible sample in 2000. In 2000, 38% of the black and Hispanic child and young adult oversamples were not fielded but were restored to the sample in 2002. Beginning in 2010, young adults over age 30 are only interviewed every other round.
1Children born to interviewed mothers; this number includes deceased and non-resident children.
2A child interview was considered complete if an interviewer was able to directly assess a child, or to obtain mother-report assessment information on the child's background and health. Child age is determined as of December 31 of the survey year.
3This total includes 37 children (age 0-4) who were assessed or interviewed whose mothers were not interviewed.
4This total includes 14 children (age 0-14) and 257 young adults whose mothers were not interviewed.
5This total includes 13 children (age 0-14) and 306 young adults whose mothers were not interviewed.
6This total includes 30 children (age 4-14) and 452 young adults whose mothers were not interviewed.
7This total includes 7 children (age 4-14) and 406 young adults whose mothers were not interviewed.
8 This total includes 7 children (age 4-14) and 490 young adults whose mothers were not interviewed.
9This total includes 15 children (age 4-14) and 551 young adults whose mothers were not interviewed.

 

Important Information

A series of variables, assigned to the "Area of Interest" called CHILD BACKGROUND, indicates interview and assessment status for both younger children and young adults. Starting in 2002, the question names for the child interview status variables follow the CINTRV format, appended with the survey year. Prior to 2000, users should rely on the child sample weight variables (CSAMWGT greater than "0") in order to determine if a child was interviewed.

  CINTRV2002-present  INTERVIEW STATUS OF CHILD

A set of created variables indicating Young Adult interview status is available from 1994 to the present survey year:

  YAINTV1994-present WAS CHILD INTERVIEWED AS YOUNG ADULT IN CURRENT ROUND?

NLSY79 mothers. Significant numbers of NLSY79 mothers have participated in the NLSY79 Child data collection effort over the years. (Users interested in the participation rates of NLSY79 mothers relative to nonmothers and other NLSY79 respondents will find details in the NLSY79 User's Guide.) Table 1 shows, for each Child survey, the proportion of women interviewed who are mothers. The table also indicates the number of children born to interviewed mothers.  When appropriate weights are applied, NLSY79 women have had, on average, about 1.9 children, which is estimated to be more than 95 percent of their ultimate childbearing. While the childbearing for this cohort is now largely completed, caution is still advised when generalizing from any selected portion of the child cohort.

Child Sample Eligibility. In the first round of the NLSY79 Child survey (1986), all children born to NLSY79 women (who were themselves interviewed) were eligible to be interviewed. Starting in 1988, children whose usual residence was outside the mother's household were excluded from the sample. This residence restriction, however, applies only to children who are not age-eligible for the Young Adult survey. Children who are part of the sample of younger children (age 0-14) must reside at least part or full time with the NLSY79 mother respondent in order to be eligible. 

From 1986-1992, there was no upper age restriction on the Child sample. Starting in 1994, children who turned 15 by the end of the survey year became part of the Young Adult sample. Until 2008, the Child and Young Adult survey periods were restricted to a single calendar year. However, starting in 2010, the field period crossed over into the following calendar year, so the Child/Young Adult samples are more clearly distinguished based on year of birth. The table below indicates the birth year range for the younger Child cohort for 2010 and 2012:

  Younger child sample Year of birth range
  R24-2010 Survey 1996-2005 (age 14 or younger as of 12/31/2010)
  R25-2012 Survey 1998-2008 (age 14 or younger as of 12/31/2012)

Young Adult Sample Eligibility. Young Adult children who have at least one record in the child interview history are generally eligible for interview regardless of their residence status. In both 1994 and 1996, children of NLSY79 mothers who would be 15 or older by the end of the survey year were eligible to be interviewed as Young Adults. In the 1998 survey year, a cap was placed on the upper ages of the Young Adults, so that only those children 15 to 20 were interviewed as Young Adults. In 2000, the full sample of eligible Young Adults was again fielded, with no upper age limit imposed; however, approximately 40% of the YAs between 15 and 20 from the black and Hispanic oversample families were not fielded in 2000 for budgetary reasons. These YAs were eligible again to be interviewed in 2002. For the 2004, 2006, and 2008 fieldings, there were also no sample restrictions for age or sample type. 

Beginning in 2010, Young Adult respondents over the age of 30 have been moved to a four-year interview cycle. Because of the structure of the Young Adult sample, in each survey round some respondents will be interviewed as Young Adults for the first time that round, some will have been last interviewed in the previous round, and some will have been last interviewed as Young Adults two (or more) rounds ago. NOTE: In the 1998 data collection only, the Young Adult sample was limited to respondents who were between the ages of 15 (by the end of the year) and 20 (at the date of interview).

Sample Restrictions and Exclusions. Over the period of the survey the following adjustments have been made to the Child and Young Adult samples:

  • 1990. Following the 1990 interview, none of the 1,643 members of the economically disadvantaged, nonblack/non-Hispanic NLSY79 main Youth sample were eligible for interview. In anticipation of the deletion of this sample, the children of the mothers in this subsample were excluded beginning with the 1990 interview and were not assessed or interviewed as Young Adults in any subsequent round. The sample nonetheless retains sufficient numbers of children from this category to maintain its full national representation. 
  • 1994. Starting in 1994, with the introduction of the Young Adult surveys, children age 15 and older become part of the young adult sample and are eligible for interview regardless of residence.  This means that, starting with the 1994 survey, the NLSY79 younger child sample was redefined as children under age 15 as of the end of the survey year.
  • 1998. In the 1998 survey year, a cap was placed on the upper ages of the young adult sample, so that only those children 15 to 20 were interviewed as Young Adults. 
  • 2000. In 2000 the criteria for both younger children and young adults under age 21 were restricted (for that survey round only) to exclude a random sample of about 38 percent of the younger children and young adults from the black and Hispanic oversamples.  This restriction means that while the full set of oversample mothers was contacted in 2000, only about 60 percent of their children under age 21 were part of the fielded sample targeted for interview. In 2002, the oversample cases that were excluded in 2000 were restored to the fielded sample eligible for interview. A flag in the database (C00115.13, CEXCLUDED2000) indicates which children under age 15 were part of the excluded oversample in 2000.
  • 2010 and beyond. Beginning in 2010, young adults over age 30 are only interviewed every four years. The interviewed sample is selected by age as of December 31 of the survey year, so that approximately half of the older young adults are eligible each round. Since 2010, young adults age 31-32, 35-36, 39- 40, 42-44, etc. as of December 31 of the target year will not be fielded.