Total number of weeks that the respondent held a job in month M of year Y. M goes from 1 to 12 and represents the calendar month. Y goes from 1 to 6 and represents the number calendar year for a given SIPP panel. Months that are outside the time frame covered by an individual's SIPP panel will always be missing and out of universe. The relevant SIPP variable is WKSJB (1984 panel), WKSJOB (1990, 1991, 1992, 1993), or RMWKWJB (1996, 2001, 2004, 2008). Values range from 0 to 5.