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Healthy worker survivor bias: implications of truncating follow-up at employment termination.

Authors
Picciotto-S; Brown-DM; Chevrier-J; Eisen-EA
Source
Occup Environ Med 2013 Oct; 70(10):736-742
NIOSHTIC No.
20043328
Abstract
Objectives: The healthy worker survivor effect is a bias that occurs in occupational studies when less healthy workers are more likely to reduce their workplace exposures. When variables on the pathway from health status to exposure are measured, g-methods can avoid this bias. However, studies in which follow-up ends at employment termination have additional potential for selection bias. This paper examines the structure of the healthy worker survivor effect, compares results with and without censoring at employment termination, and addresses how to prevent bias when such censoring occurs. Methods: G-estimation of structural accelerated failure time models was applied in the United Autoworkers-General Motors cohort study to examine relationships between metalworking fluid exposure and cause-specific mortality. Subjects were followed from hire through 1994, regardless of employment status. To answer the central question, g-estimation analysis was repeated after truncating at employment termination and censoring outcomes that occurred thereafter, with adjustment for censoring by inverse probability weighting. Results: Using full follow-up time, HRs were estimated for all-cause mortality (1.09), ischaemic heart disease death (1.19), and death from any cancer (1.09), comparing 5 years of metalworking fluid exposure to no exposure. For all three outcomes, the HR estimates based on data censored at termination of employment were below 1 (respectively, 0.92, 0.97, 0.79). Conclusions: In this application, g-estimation together with weighting did not prevent selection bias due to employment termination. However, the bias might be avoided in studies with measured health-related variables on the pathway from health status to employment termination.
Keywords
Worker-health; Survival-rate; Exposure-assessment; Surveillance-programs; Analytical-instruments; Analytical-processes; Automotive-industry; Metalworking-fluids; Mortality-data; Mortality-rates; Data-processing; Quality-control
Contact
Dr. Sally Picciotto, Division of Environmental Health Sciences, UC Berkeley School of Public Health, 789 University Hall, Berkeley, CA 94720, USA
CODEN
OEMEEM
Publication Date
20131001
Document Type
Journal Article
Email Address
sallypicciotto@berkeley.edu
Funding Type
Grant
Fiscal Year
2014
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-R01-OH-009939; Grant-Number-R01-OH-008927; Grant-Number-R03-OH-010202; Grant-Number-R01-OH-010028; M112013
Issue of Publication
10
ISSN
1351-0711
Source Name
Occupational and Environmental Medicine
State
CA
Performing Organization
Stanford University
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