Seam Effect

The seam effect, also called the seam bias, a phenomenon specific to longitudinal panel surveys, refers to the tendency for estimates of change, as measured across the "seam" between two successive survey administrations (or "waves"), to far exceed change estimates that are measured within a single survey wave—often by a factor of 10 or more. Seam effects have been found in virtually every panel survey examined, regardless of the characteristics under study, the data collection methods, or the length of the recall period. Seam bias almost always signals the presence of serious measurement error, which can severely compromise the statistical utility of estimates of change. A considerable amount of research over the past two decades has documented the existence of seam effects in longitudinal surveys ...