Total number of weeks worked with pay 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 wkswp_Y_M variable is calculated by subtracting the weeks without pay in month M of year Y from wksjob_Y_M. The relevant SIPP variable for weeks without pay is WKSWOP (1984, 1990, 1991, 1992, and 1993 panels), or RMWKSAB (1996, 2001, 2004, 2008). Values range from 0 to 5.