Identifying comparison groups for evaluating occupational hearing loss: A statistical assessment of 22 industrial populations

Finding appropriate comparison groups to study occupational hearing loss has been difficult. Recently, however, the National Institute for Occupational Safety and Health sponsored the compilation of potentially useful data from 22 diverse industrial companies in the U.S.A. and Canada. We conducted a statistical evaluation to determine which of the 22 populations might be suited as comparison groups in future studies of workers exposed to hazardous noise. In a Cox Proportional Hazards model that included age and sex, the relative risk of developing hearing loss in each company was estimated at two, five, and ten years of follow-up. We ranked the companies based on their relative risks, and rated them on a five-point scale from 'excellent' to 'poor' to indicate their suitability as comparison groups. The risk profiles developed and other variables described in this study will assist researchers in selecting appropriate comparison groups for evaluating occupational hearing loss.