The Survey of Income and Program Participation (SIPP) is a major household survey conducted by the Census Bureau, which is intended to be an important source of information on the economic situation of persons and households in the United States. In the current design a new sample panel is selected each year. A person in a SIPP panel is generally interviewed eight times over a period of 2 2/3 years, with each round or wave of interviewing collecting information for each month of a four month reference period. Although the survey has cross-sectional uses, a major interest is in longitudinal estimates. Under current procedures, a sample person who misses any interviews may be excluded from the longitudinal estimates, sometimes, as explained later in the paper, even for estimates for time intervals which do not overlap any missed interviews. Concern has been expressed by some data users, particularly the Food and Nutrition Service (FNS), over the detrimental effects on both variances and biases of the exclusion of these sample cases, particularly the cases that miss some interviews but later return to sample. The purpose of this paper is to investigate the implications of this exclusion and to consider alternative approaches.