The topical modules contain more detailed information on particular topics than are contained in the core files. We used data from the topical modules to construct explanatory variables for the multivariate analysis.
The wave 1 topical module contains retrospective information on sample members' prepanel activities and experiences. The most important such information for this study concerns prepanel employment experiences (including the number of years the respondent worked at least six months, breaks from the labor force, the date last worked, and whether the respondent generally worked 35 or more hours per week since he or she first started working at least six months per year). Unlike previous SIPP panels, information on the starting dates for those in the middle of job spells at the start of the SIPP panel period (that is, who have left-censored job spells) are in the wave 1 core file and not in the topical module.
Several topical modules contain information on work schedules and health status. Data on work schedules are contained in the wave 4 and wave 10 topical modules. However, as discussed later, most of our analysis was conducted using samples of workers who began low-wage jobs at the start of the panel period (that is, in waves 1 and 2), and our analysis described the characteristics of low-wage workers and their jobs at the start of these jobs. Thus, the data on work schedules was collected too late to be useful for our study, so we did not use them in the analysis. For a similar reason, we did not use the detailed information on functional limitations and disabilities contained in topical modules 5 and 11.(6) However, we did use in the analysis the health status variable contained in each core data file concerning whether the respondent had a physical, mental, or other health condition that limited the kind or amount of work that could be done.