This report uses data from the Survey of Income and Program Participation (SIPP) to examine the incidence of poverty at a point in time and over a 32-month period. It presents data from the complete panel file of the 1990 SIPP which covers the time period from October 1989 through August of 1992. Descriptions of the SIPP program and the 1990 panel file are contained in appendixes A and D, respectively.

SIPP enables comparisons of poverty rates among groups of persons of different demographic and socioeconomic characteristics. It also can be used to study the distribution of poverty spell durations. The panel file contains monthly information on income as well as on many other characteristics which can vary over the panel, such as residence and labor force status. Efforts were made during the life of the panel to follow persons who moved to ensure that the sample remained representative of the noninstitutional population of the United States. Persons are characterized by the income and poverty status of their respective family unit based on living arrangements each month during the period of study.

It should be noted that some longitudinal estimates presented here are based on responses of persons who were interviewed in all eight waves of the 1990 panel. Other longitudinal estimates are based on respondents interviewed in all waves of a particular calendar year. Insofar as persons who left the panel differed in their experience of poverty from those who did not, these longitudinal estimates may be biased.