Discontinuity in estimates of monthly poverty rates across successive panels of the Survey of Income and Program Participation (SIPP) has been a consistent feature of SIPP Panels since the 1996 redesign. As investigated by Czajka, Mabli, and Cody (2008), each SIPP Panel since 1996 has reported Wave 1 poverty rates that were at least two percentage points higher than the final wave of the preceding panel. Additionally, within SIPP Panels, monthly poverty rates experience sharp declines between Waves 1 and 2. This across and within panel phenomenon is generally referred to as the "Wave 1 effect."

Building off of prior research on the Wave 1 effect in earlier SIPP Panels (Czajka, Mabli, and Cody 2008; Anderson and Fields 2010), this analysis examines the Wave 1 effect in the 2008 SIPP Panel, with comparisons to the preceding 2004 SIPP Panel. Discrepancies in monthly poverty rates across panels and waves are investigated with a focus on sample composition changes and within-person poverty transitions across successive waves of the 2008 Panel.

The research suggest that the magnitude of the Wave 1 effect in the 2008 SIPP Panel was consistent with the effect observed in the 2004 Panel. However, the impact of within-