Total number of weeks that the respondent held a job in month M. M represents the month number since the start of panel_1stfullyear. Only the first 24 months of the individual's SIPP panel are in universe for panels 1984, 1990, 1991, 1992, 1993, 2001. Panels 1996 and 2008 go up to month 48 and panel 2004 goes up to month 36. A later release of these data will add months after 24 for longer SIPP panels. Months that are outside the time frame covered by an individual's SIPP panel will always be missing and out of universe.