Use of city directories as a source of occupational data in a case-control study.

The association between occupational factors and male breast cancer was investigated in a population-based case-control study conducted in Western New York state. Since 9% of cases and controls were missing occupational information in the tumor registry (usual occupation) and screening clinic (type of work done) files, supplemental occupational data were collected from commercial city directories. Occupational data were located for 69% of participants via the city directory thereby reducing the missing occupational data to 3%. For individuals with occupational listings in both the original source document and the city directories, similar titles were found for 94% of cases. Factors to be considered in assessing the feasibility of directory usage include purpose of study, degree of directory coverage within the geographic area, gender of participants, and availability of personnel and resources. City directories are a valuable supplemental source of occupational data for hypothesis generating case-control studies or registry-based studies of men conducted in urban areas.