The Survey of Income and Program Participation (SIPP) is a national longitudinal survey, conducted by the U.S. Bureau of the Census, which collects detailed information on income and wealth. The information collected includes employment income and income received from government transfer programs at the person, family, and household levels. The survey uses a rotating panel design, with a new panel of sample households being introduced at the start of each calendar year. Each panel is divided into four approximately equal rotation groups. Each month households from a different rotation group are interviewed. During each interview, the respondent is asked to provide information for the preceding four months. The four-month cycle, in which all of the households of the panel are interviewed, is referred to as a wave. The number of waves in a panel is determined by the length of the panel. Through 1995, households in most of the SIPP panels had been interviewed once every four months over a period of 32 months. Starting with the 1996 panel, the length of the panel will increase to four years with a new panel being introduced once the old panel is completed.