Occupational exposure guidelines are ideally based on estimated effects of static interventions that assign constant exposure over a working lifetime. Static effects are difficult to estimate when follow-up extends beyond employment because their identifiability requires additional assumptions. Effects of dynamic interventions that assign exposure while at work, allowing subjects to leave and become unexposed thereafter, are more easily identifiable but result in different estimates. Given the practical implications of exposure limits, we explored the drivers of the differences between static and dynamic interventions in a simulation study where workers could terminate employment because of an intermediate adverse health event that functions as a time-varying confounder. The two effect estimates became more similar with increasing strength of the health event and outcome relationship and with increasing time between health event and employment termination. Estimates were most dissimilar when the intermediate health event occurred early in employment, providing an effective screening mechanism.
From the School of Public Health, University of California, Berkeley, CA.
Submitted September 15, 2017; accepted May 2, 2018.
The code for simulating datasets and conducting analyses is provided in the eAppendix; http://links.lww.com/EDE/B350.
Preparation of this article was supported by grants #1R01OH010228 (P.I. Ellen A. Eisen), and #T42OH008429 (M.A.I.), by the National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention, and Department of Health and Human Services.
The authors report no conflicts of interest.
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Correspondence: Ellen A. Eisen, Division of Environmental Health Sciences, School of Public Health, University of California, 50 University Hall #7360, Berkeley, CA 94720. E-mail: firstname.lastname@example.org.