Every round of the NLSY79 has included a section on fertility. The first three rounds of the NLSY79 (1979, 1980, and 1981) have very short fertility sections.

Fertility history

Researchers can create fertility event histories in a number of ways. One method is to extract the variables from each year's survey data which record when each child was born. However, NLSY79 data show that this is not an accurate method for creating an event history. In each survey, respondents are asked to correct information in the fertility roster. (Prior to 1993, this was the Children's Record Form or CRF. Beginning in 1993, this is the BIO/NBIO Child Roster). Each year, numerous changes are made. For example, in the 1994 survey, parents changed some portion of the birth record for 548 children. While this number appears high, the vast majority of changes are to the spelling of children's names.

Because the raw recorded data on dates of birth, sex, and status (adopted, deceased) entered on the Children's Record Form (CRF) are subject to interviewer as well as respondent error, NLSY79 staff created a fertility event history beginning in 1982. This was done to aid users and, at the same time, evaluate the quality of the NLSY79 fertility data. This series, found in the "Fertility and Relationship History/Created" area of interest, lists a number of variables including the birth month, and year of every child born to NLSY79 respondents; numbers and outcomes of pregnancies; ages of respondents at the birth of selected children; dates of death for children who have died; and usual residence of children.

Age at first birth

Beginning in 1982, every NLSY79 data release has included a created variable that tracks the age of respondents when they first give birth. Readers can also find created variables in the "Fertility and Relationship History" area of interest that track how old the respondent was when the second and third births occurred.

Fertility expectations and desires

The fertility section provides researchers with an opportunity to examine whether expectations about the future compare accurately with what actually happens in respondents' lives. In 1979 and 1982, respondents were asked how many children they desired. 

In 1979, 1982, 1983, 1984, 1985, 1986, 1988, 1990, 1992, and 1994-2012, respondents also reported on the number of children they actually expected to have. After 2012, the question was no longer asked.

Fertility and relationship history

The 2000 release of the NLSY79 data introduced a new series of constructed variables for each survey year that provide information about the respondent's relationship status. All surveys were examined to match names of spouses or partners for the entire administration of the NLSY79. The first variable provides information about the respondent's total number of spouses or partners since 1979 and can range from 0 to 9. The percentage of respondents who have never reported having a spouse or partner can be found in Table 2.

Second, a unique code is assigned to each new spouse/partner at the interview date. If the same spouse or partner resides with the respondent during the next survey round, the spouse or partner code remains the same. If the respondent has a new spouse or partner, the next available number is given to that person. If in a later survey round the respondent is reunited with a previous spouse or partner, the number of spouse/partners is not increased, and the code for that year reflects that spouse/partner's original number.

The second created variable reveals whether the person living with the respondent is a spouse, coded 1, or a partner, coded 33. In some instances, the exact relationship is indeterminate in a given round; in these cases, a code of 36 is used. If no spouse or partner is present at a given survey point, but the respondent has reported a spouse/partner in the past, their relationship code will be zero. Respondents with no known spouses/partners receive a code of -999. 

There is no guarantee that the same individual(s) were present between survey rounds or that all partners are accounted for, as a spouse or partner may have appeared between survey rounds but not have been present at any survey point. Early examination suggests that this applies to only a modest proportion of cases. In some instances, identification of spouses who only were present between rounds may be possible by using the NLSY79 marriage history, as well as the marriage transition information available at each survey point.

References

Mott, Frank L., Paula Baker, R. Jean Haurin, and William Marsiglio, "Fertility Related Data in the 1982 National Longitudinal Survey of Work Experience of Youth: An Evaluation of Data Quality and Preliminary Analytical Results." Columbus, OH: CHRR, The Ohio State University, 1983.

Mott, Frank L. "Evaluation of Fertility Data and Preliminary Analytical Results from the 1983 (Round 5) Survey of the National Longitudinal Surveys of Work Experience of Youth." Columbus, OH: CHRR, The Ohio State University, 1985.

Mott, Frank L. "Male Data Collection: Inferences from the National Longitudinal Surveys." Columbus, OH: CHRR, The Ohio State University, 1998.