In 1983 the Bureau of the Census initiated the Survey of Income and Program Participation (SIPP), a survey designed to measure the economic and social changes in persons lives over time. The survey relies on a national household sample, with inperson interviews of all persons ages 15 and over. Households are in sample for a total of 32 months and are visited by an interviewer every four months (for a total of 8 interviews). During each interview (referred to as a "waven), subjects are asked questions about their employment, economic situation and program participation for each of the preceding four months. Each wave of the survey is processed separately, and only after all waves are collected are all of the data brought together to produce a full 32-month longitudinal file. In this respect, the SIPP is administered and processed much like a series of conventional cross-sectional surveys. The primary difference is that individuals and sampled households are followed (for example, if they physically change residences) with the intention of ultimately being able to provide a full 32 months of longitudinal data for each respondent.