Do panel surveys make people sick? US arthritis trends in the Health and Retirement Study.

Researchers have long viewed large, longitudinal studies as essential for understanding chronic illness and generally superior to cross-sectional studies. In this study, we show that (1) age-specific arthritis prevalence in the longitudinal Health and Retirement Study (HRS) from the United States has risen sharply since its inception in 1992, and (2) this rise is almost surely spurious. In periods for which the data sets are comparable, we find no such increase in the cross-sectional National Health Interview Survey (NHIS), the primary source for prevalence data of chronic conditions in the US. More important, the upward trend in the HRS is not internally consistent: even though prevalence in the HRS rises sharply between 1992 and 1996 for 55-56 year-olds, the prevalence for that age group plummets to its 1992 level among the new cohort added in 1998 and then rises rapidly again between 1998 and 2002. We discuss possible reasons for these discrepancies and demonstrate that they are not due to sample attrition in the HRS.