Objectives: The aim of this study was to measure the extent to which the association between socioeconomic status and laryngeal cancer among males is mediated by smoking, alcohol consumption, and occupational exposure.
Methods: We used Karlson et al's decomposition method for logit models, which returns the percentage of change in odds ratios (OR) due to confounding. This population-based, case-control study on laryngeal cancer was conducted in Germany in 1998-2000 and included 208 male cases and 702 controls. Information on occupational history, smoking, alcohol consumption, and education was collected through face-to-face interviews. Jobs coded according to ISCO-68 were linked to a recently developed job-classification index covering physical and psychosocial dimensions. A sub-index focused on jobs involving potentially carcinogenic agents (CAI) for the upper-aero digestive tract.
Results: When adjusted for smoking and alcohol consumption, higher OR were found for lower education. This OR decreased after further adjustment using the overall job index [2.9, 95% confidence interval (95% CI) 1.4-6.2], similar to the OR using the sub-index CAI (OR 2.7, 95% CI 1.3-5.8). Applying the Karlson et al method, 25.4% (95% CI 22.6-28.2%) of the reduction in these OR was due to occupational exposure (CAI), while smoking and alcohol consumption contributed to around 26.1% (95% CI 23.2-28.9%) and 2.7% (95% CI 1.7-3.8%), respectively.
Conclusions: Occupational aspects, in particular the exposure to carcinogenic agents, explain a large portion of the association between low educational level and laryngeal cancer risk among males. Occupational effects are now easier to quantify using this recently developed and easily applicable index.