INITWGT contains the base survey weight for the sample unit to which the sample person belongs. This base survey weight is the inverse of the probability of selection for the sample unit, adjusted only for unit non-response and, in rare instances, for sampled units that turned out to represent more than one separate residence. Unlike final panel and calendar year weights, INITWGT includes no adjustment for attrition of households from SIPP panels and are not adjusted at the person level to match any external controls. SSB users can utilize the weights to produce estimates that account for idiosyncratic probability of selection of sample units and for unit-nonresponse. Estimates for each SIPP panel, using these weights, become representative of the U.S. non-instutionalized population as of the beginning of the panel. For instance, using INITWGT, the distribution of calendar year 2010 administrative earnings for sample persons in the SSB from the 1984 SIPP panel would be representative of the U.S. population as of calendar year 1984.