found men who were employed in exposed occupations during the 1960s (but not the 1970s) to have increased leukemia. They suggested that exposure was decreased due to changing work practices in the later time period.

Methodologically, these more recent studies are clear improvements on the earlier studies that relied on job titles alone. The investigators developed rather elaborate approaches for classifying exposures more accurately and taking potential confounders into account. In spite of those refinements, the patterns of association have not become more consistent and pronounced, nor have they gone away. The relative risks in the upper categories of 2-3 reported in the high-quality studies of Floderus et al. (1993) and Theriault et al. (1994) cannot be ignored. However, the inconsistency in which cancer types show increased risks, the presence of contradictory studies (e.g., Sahl et al. 1993), and the irregular dose-response gradients make the interpretation problematic. Overall, the most recent studies have increased rather than diminished the likelihood of an association between occupational exposure to electric and magnetic fields and cancer, but they have failed to establish an association with a high degree of certainty.

Another avenue of research to be noted is the concern with occupational exposure to electric and magnetic fields and breast cancer. A series of three studies reported an association between electrical occupations and male breast cancer (Tynes and Andersen 1990; Matanoski et al. 1991; Demers et al. 1991), which were similar in character to the initial studies of leukemia and brain cancer. More recently, a report of no association was published (Rosenbaum et al. 1994). Female breast cancer in relation to electrical occupations was evaluated by Loomis et al. (1994) among a large number of decedents in the United States. A modest increase in risk was found for women in electrical occupations, particularly telephone workers, encouraging further evaluation of a potential link between exposure and this common cancer.

REPRODUCTION AND DEVELOPMENT

Epidemiologic studies of potential adverse reproductive effects of exposure to electric and magnetic fields are limited in quantity and, to some extent, in quality. There are a multiplicity of exposure sources of potential interest (including residential exposures from power lines, occupational exposures from video-display terminals (VDTs), and other exposures from electric appliances, such as electric blankets) as well as a diversity of reproductive health end points (including infertility, miscarriage, congenital defects, growth retardation, and preterm delivery). Most of those areas have been addressed in fewer than three studies, the exception being VDTs in relation to spontaneous abortions. Although grouping data for exposures from all types of sources with the relevant outcomes is tempting for review purposes, comparing studies of similar types of exposures and outcomes without the assumptions required for aggregation is more constructive. The absence of efforts to replicate these studies is the predominant source



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