Combined Occupational and Residential Exposures (invited paper)

The most complete coverage of exposure to extremely low frequency magnetic fields has been reached in studies of childhood cancer. In studies of adults, disregarded exposure is a more relevant issue and the potential impact on study results is not well known. As a rule, one environment at a time, residential or occupational, has been examined. Disregarded exposure results in misclassification of overall exposure, but there will always be a specificity of 100%. Subjects without exposure either at home or at work, will all be classified as unexposed. The influence of disregarded exposure on study results depends on the relationships between the focused and the disregarded exposure, and on the relationships between the two exposures and disease outcome. Simulations indicate that relative risks based on occupational exposure only are close to estimates based on combined data. A more precise assessment of either exposure can be more important than combining residential and occupational exposure. In risk assessments, on the other hand, it is misleading if, for example, only residential exposure is considered, since the prevalence of exposure from other environments is far from marginal. (author)