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 and screening clinic 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%.