Beginning with the release of the 2000 data, the Work History file is incorporated into the main NLSY79 data set. Variables previously located on the separate Work History file can be identified by searching for areas of interest beginning with "Work History." In addition, the reference numbers for work history variables begin with "W." Key work history variables are described below.

Weekly Arrays: Week-by-week records of the respondent's labor force status and associated job(s), if employed, and the total number of hours worked each week at any job, if employed, are available. This information is contained in the three arrays described above.

Although data on only up to five jobs are released, data are collected on all jobs. Data for the extra jobs are used to construct summary KEY variables by the work history programs. The number of jobs has exceeded ten for one case in 1991 and 1992, two cases in 1998, and one case in 2000.

Many researchers focus on data for the CPS job. Because the CPS was Job #1 only in select years, researchers should see the "Important Information" box in the Labor Force Status section for an elaboration of this concept.

Employment Gaps: Gaps within tenure with a specific employer are reported in association with that employer. They occur between the start and stop dates given for an employer. The respondent does not consider himself/herself completely disassociated from the relevant employer during these periods, although he or she was not actively working for that employer. Specific variables for each gap include start and stop dates; the reason that the respondent was not working; the number of weeks that a respondent was unemployed (looking for work or on layoff) or out of the labor force (OLF or not looking for work); and, for those who were OLF at some time during a gap, the reason they were not looking for work. See the Work Experience section for a discussion of gaps with respect to job tenure.

Gaps between employers are gaps in a respondent's employment during which he or she was not associated with any employer. The specific variables collected with respect to "within job gaps" (see the discussion in the Work Experience section on tenure with a specific employer) are also collected with respect to gaps between employers, with the exception of the reason that the respondent was not working during the gap.

The information collected on reasons for employment gaps allows specific dates to be fixed for unemployed or OLF status only if a respondent was unemployed or OLF for the entire period of the gap. If the respondent was unemployed for part of the gap and OLF for the other part, the number of weeks unemployed and OLF is recorded, but the specific dates of periods for which the respondent was actively looking for work/on layoff and not looking for work are not collected. This prevents the Work History program from assigning specific week numbers to these statuses in the event of such a "split gap." Instead, the number of weeks reported as unemployed is assigned to the middle of the total gap period, with the remainder of weeks at the beginning and end of the gap period being assigned an OLF status. Users examining the week-by-week status array containing labor force statuses should be aware that "split gaps" will appear as a series of "5" codes, followed by a series of "4" codes, followed by another series of "5" codes (5 5 5 5 5 .... 4 4 4 4 4 .... 5 5 5 5 5). Although the start and stop dates for the whole gap will be those actually reported by the respondent, the assignment of the unemployed and OLF statuses will not represent actual dates reported by the respondent. They represent only the number of weeks that a respondent reported having held each status, with the unemployed status being arbitrarily assigned to the middle portion of the gap.

Summary Labor Force Related Variables: Variables are constructed summarizing different aspects of a respondent's labor force activity, including total number of hours worked, weeks worked, weeks unemployed, weeks out of the labor force, and weeks in active military service. There are two sets of these variables, referring to each of two time periods--the period since the last interview and the past calendar year (see the Labor Force Status section). Variables are also created indicating the number of weeks since the previous interview and the percent of weeks for which a definite status cannot be determined in constructing the summary variables discussed above. See the Work Experience section for further notes on these variables.

Tracing Employers Back Through Contiguous Survey Years: Of particular interest to many researchers have been the PREV_EMP# and TENURE variables associated with each employer. The PREV_EMP# allows a respondent's association with a given employer to be traced back through contiguous survey years. Using PREV_EMP# and the appropriate start and stop dates, a TENURE variable is constructed for each job reported, which depicts total weeks of tenure with each employer across contiguous survey years. Examine the work history documentation in Appendix 18 to determine if any such time-saving variable constructions exist. 

Creation of the Work History Data

The work history is a complete retrospective up to and including the respondent's most recent date of interview. The questions in these survey sections are constructed to collect a complete history for each respondent, regardless of period of noninterview. For example, a respondent previously interviewed in 1984 and not interviewed again until 1989 will have a complete labor force history as of the 1989 interview, as information for the intervening period will be recovered in the 1989 interview. The Work Experience section contains a discussion of possible discrepancies or inconsistencies in these data. Researchers should be aware that, although such possibilities exist, they have not appeared to be a major factor in the quality or completeness of the work history record.

Be aware that for respondents with simultaneous active military status and civilian employment status, civilian labor force activity will take precedence over military status. For the purposes of constructing the week-by-week status array, the civilian job number will replace the military status code for weeks in which both statuses occur. The order of precedence for various labor force status codes is detailed in the work history documentation (see the discussion of the work history PL/I program in Appendix 18 of the NLSY79 Codebook Supplement); see also the Work Experience section.

For purposes of constructing the status array and computing the summary labor force activity variables, the work history programs require that specific week numbers be assigned on the basis of the job-specific start and stop dates. In the event that missing data occur in the job-specific start and stop dates, the programs take one of two actions. 

1. If only the day in a given date is missing, the program assigns the number "15," placing these dates in the middle of the month. This allows an approximate week number to be assigned. The possibility still exists, however, that a negative job/gap duration will result because the day is arbitrarily fixed. For example, a start date of 10/-2/90, which indicates a missing day, and a stop date of 10/6/90 would be read by the work history program as 10/15/90 and 10/6/90 respectively. Therefore, when the week numbers are assigned, the arbitrary assignment of "15" as the start day would give an erroneous impression that a job started after it stopped. The status array and computed summary variables will reflect the invalid data in the week numbers.
2. Dates missing a month or year cannot be estimated by the work history program and therefore have invalid missing codes for the week numbers. The status array and other computed variables cannot be calculated for activity within periods for which either or both of the dates have such missing information. These will also register invalidly missing information for any period in which specific dates and week numbers cannot be determined.

Comparison to Other NLS Cohorts: The NLSY97 Event History file contains created variables summarizing the month and year in which major life events occurred for each respondent, along with all main file data. Variables cover topics such as marital status, enrollment, employment status, and program participation. The NLSY97 Event History file presents employment status information in a format similar to the NLSY79 employment information, using a continuous week timeline. Although the NLS has collected information on labor force behavior since its inception, only partial work histories for respondents in the Original Cohorts can be constructed for certain survey years. The degree of completeness of the work history data varies by cohort and survey year. For more precise details about the content of each survey, consult the appropriate cohort's User's Guide using the tabs above for more information.