The seam effect is a well-known phenomenon associated with longitudinal surveys, such as the Survey of Income and Program Participation (SIPP). The "seam" derives its name from the abutment of consecutive survey reference periods, about which survey enumerators collect various kinds of information in interviews. The "seam effect" is observed when the information collected for the end of one reference period (based on one interview) is compared to the information collected for the beginning of the next reference period (based on another interview). Survey researchers have found that there is a tendency for a greater amount of change in information to be reported at the seams of reference periods than within reference periods.