Survey Research And Methodology Program


Date of this Version

May 2007


This PhD dissertation in Survey Research and Methodology was written under the supervision of Professor Robert. F. Belli. Members of the committee were professors: Dan Hoyt, Brian Bornstein, Allan McCutcheon and Jon Krosnick


A seam effect occurs in panel studies when within-wave changes are less frequent than between-wave changes (comparing data gathered from two different interviews). This study explores the changes in the magnitude of seam effects among labor force states (employment, unemployment, not in labor force) using the last seven waves of the Panel Study of Income Dynamics collected between 1995 and 2005. The panel underwent several changes: data were collected with conventional questionnaires (CQ) until 2001. The interval between waves was changed from one year to two years in 1997. The data regarding labor force transitions were collected with Event History Calendar (EHC) instruments starting in 2003. The questionnaire was also changed: one modification took place when implementing the two year recall period and the second when starting data collection with EHC.

Data collected with EHCs show a decrease of seam effects in comparison to the previous waves collected with CQ on a two year recall period. A new undocumented phenomenon was also found in the data. When implementing the two year recall period in the CQ waves, a within-wave seam effect appeared, that is a seam effect between the first year and the second year of the two-year reference period reported in the same interview. This effect disappeared in EHC interviews and is most likely due to a change in the questionnaire design. The estimates of labor status changes most affected by seam bias were the transitions from “employed” to “not in the labor force”, and from “not in the labor force” to “employed”, regardless of the data collection methodology or the length of the recall period. Lastly, the magnitude of one year recall period seam bias was lower than any two year recall period seam points. The results are discussed in light of theories of seam effects, questionnaire design, and with references to the literature on EHC and CQ interviewing methods.