Do panel surveys really make people sick? A commentary on Wilson and Howell (60:11, 2005, 2623-2627)

In a recent article in this journal, Wilson and Howell [2005. Do panel surveys make people sick? US arthritis trends in the Health and Retirement Survey. Social Science & Medicine, 60(11), 2623-2627.] argue that the sharp trend of rising age-specific arthritis prevalence from 1992 to 2000 in the USA among those in their 50s based on the original Health and Retirement Study (HRS) cohort of respondents is "almost surely spurious." Their reasons are that no such trend is found in the National Health Interview Study (NHIS) over this same time period, and that an introduction of a new birth cohort into HRS in 1998 also indicates no trend. They also claim that there may be an inherent bias in panel surveys leading respondents to report greater levels of disease as the duration of their participation in the panel increases. This bias, which they call "panel conditioning," suggests a tendency for participants in a longitudinal survey to seek out medical care and diagnosis of symptoms asked about in previous waves. In this paper, we show that the evidence presented and the conclusions reached by Wilson and Howell are incorrect. Properly analyzed, three national health surveys--the NHIS, National Health and Nutrition Examination Survey (NHANES), and HRS--all show increases in age-specific arthritis prevalence during the 1990s. Since the new HRS sample cohort introduced in 1998 represents only a part of that birth cohort, we also demonstrate that Wilson and Howell's evidence in favor of panel conditioning was flawed. We find little indication of panel conditioning among existing participants in a panel survey.