The healthy worker effect: Do health problems predict participation rates in, and the results of, a follow-up survey?

Purpose To determine the impact of the healthy worker effect (HWE) as a bias for the external and internal validity of the follow-up assessment in prospective survey research. Specifically, the study examined (1) whether the health status of respondents at the baseline measurement influenced response at the follow-up survey (external validity) and (2) whether HWE is a threat to internal validity by differential attrition, i.e., whether associations between work and health at baseline differ between stayers and dropouts. Methods In a two-wave questionnaire survey with a 2-year time lag comprising 6283 persons, 4392 responded at both time points (response rate 70 %). Mental distress and somatic symptoms served as indicators of health. Role conflict and role clarity were indicators of work factors. Results There were few differences in response rate at follow-up between persons with and without health complaints at the baseline measurement. As response rate increased incrementally with educational level, there seems to be a socio-educational bias, rather than a HWE bias on survey participation. Baseline relationships between work factors and health indicators were equal in magnitude among stayers and dropouts. Conclusion The health status of participants at baseline seems to have little impact on the external and internal...