Exposure to ionizing radiation and risk of cutaneous malignant melanoma. Search for error and bias

In a 1984 case-control study of cutaneous malignant melanoma (CMM) among workers at the Lawrence Livermore National Laboratory, Austin and Reynolds found an association between reported employment in proximity to ionizing radiation and CMM (odds ratio (OR) = 5.4; 95% confidence interval (CI): 1.4, 20.7). But in a preliminary study in 1981, they found no association between individual radiation dosimetry readings and CMM. We reanalyzed the 1984 Austin-Reynolds case-control data to determine whether error or bias explain the inconsistency between reported employment in proximity to radiation and individual radiation dosimetry readings. Using individual radiation dosimetry readings, we developed an index of occupation-specific radiation. This index was associated with case status (OR = 10.8; 95% CI: 1.4, 85.1). No definitive evidence for influential matched sets, confounding, recall bias, or any other sources of bias was identified. These results suggest that the odds ratio for reported employment in proximity to radiation may be valid.