Abstract
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 validity of the follow-up assessment in prospective survey research. Hence, the findings provide little support to the HWE as a potential bias in prospective studies within occupational health research. A limitation of the study is that the findings do not inform about the impact of the HWE on participation in the baseline assessment.
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Acknowledgments
This study was funded by the Norwegian Research Council. The authors thank the participating companies for their willingness to participate, and Bjørn Lau, Anne Lene Andersen, Shahrooz Elka, Margrethe Schøning, Elisabeth Petersen, and Jan S. Emberland for their assistance in the survey administration.
Conflict of interest
The authors have no conflicts of interest related to the work described in this article.
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Nielsen, M.B., Knardahl, S. The healthy worker effect: Do health problems predict participation rates in, and the results of, a follow-up survey?. Int Arch Occup Environ Health 89, 231–238 (2016). https://doi.org/10.1007/s00420-015-1066-6
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DOI: https://doi.org/10.1007/s00420-015-1066-6