Lung Cancer Mortality and Carbon Black Exposure: Uncertainties of SMR Analyses in a Cohort Study at a German Carbon Black Production Plant

OBJECTIVE: We undertook a sensitivity analysis of the lung cancer standardized mortality ratios (SMRs) in a study of 1522 German carbon black workers from 1976 to 1998. METHODS: We applied results from a case-control study to adjust the SMR for smoking habits and exposures experienced before the carbon black job. In addition, sensitivity to reference rates was explored. RESULTS: On the basis of 47 lung cancer deaths, the SMRs were 1.62, 1.72, and 2.08 (local, state, and national rates, respectively). Adjustment for previous exposures and smoking yielded additional correction factors of 0.64 or 0.74, varying with the chosen reference. CONCLUSIONS: Lung cancer SMRs (95% confidence intervals) for the full cohort ranged from 1.20 (0.88-1.59) to 2.08 (1.53-2.77) in this sensitivity analysis. Thus, overall SMRs are only weak measures of causal associations and should be complemented by internal modeling of exposure effects whenever possible.