Estimating the effect of cumulative occupational asbestos exposure on time to lung cancer mortality: using structural nested failure-time models to account for healthy-worker survivor bias.
BACKGROUND
Previous estimates of the effect of occupational asbestos on lung cancer mortality have been obtained by using methods that are subject to the healthy-worker survivor bias. G-estimation of a structural nested model provides consistent exposure effect estimates under this bias.


METHODS
We estimated the effect of cumulative asbestos exposure on lung cancer mortality in a cohort comprising 2564 textile factory workers who were followed from January 1940 to December 2001.


RESULTS
At entry, median age was 23 years, with 42% of the cohort being women and 20% nonwhite. During the follow-up period, 15% of person-years were classified as occurring while employed and 13% as occupationally exposed to asbestos. For a 100 fiber-year/ml increase in cumulative asbestos, a Weibull model adjusting for sex, race, birth year, baseline exposure, and age at study entry yielded a survival time ratio of 0.88 (95% confidence interval = 0.83 to 0.93). Further adjustment for work status yielded no practical change. The corresponding survival time ratio obtained using g-estimation of a structural nested model was 0.57 (0.33 to 0.96).


CONCLUSIONS
Accounting for the healthy-worker survivor bias resulted in a 35% stronger effect estimate. However, this estimate was considerably less precise. When healthy-worker survivor bias is suspected, methods that account for it should be used.
From the aDepartment of Epidemiology, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC; and bDepartment of Biostatistics, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC.
Ashley I
AI
Naimi
Stephen R
SR
Cole
Michael G
MG
Hudgens
David B
DB
Richardson
D000328:Adult; D000395:Air Pollutants, Occupational / Q000009:adverse effects*; D001194:Asbestos / Q000009:adverse effects*; D015982:Bias; D005260:Female; D005500:Follow-Up Studies; D015989:Healthy Worker Effect; D006801:Humans; D008175:Lung Neoplasms / Q000209:etiology / Q000401:mortality*; D008297:Male; D015233:Models, Statistical; D009784:Occupational Diseases / Q000209:etiology / Q000401:mortality*; D016273:Occupational Exposure / Q000009:adverse effects*; D013022:South Carolina / Q000453:epidemiology; D013783:Textile Industry; D013997:Time Factors
D000395:Air Pollutants, Occupational; D001194:Asbestos