of Severson et al. (1988) of adult leukemia, and no association with the disease was found.

A second refinement in the wire codes was made by Kaune and Savitz (1994) that resulted in a smaller number of categories, a larger proportion in the highest interval, and a similar predictiveness for magnetic fields. The risk estimates produced by using this modified (three-category) code are larger than those based on the dichotomized results (HCC and LCC) and more precise than those from the five-level wire code used in the 1988 study (Savitz and Kaune 1993). These increases in relative risks combined with improvements in accuracy of the modified wire codes as an indicator of residential magnetic-field strength lend some support to the hypothesis that magnetic fields might be associated with cancer.

Magnetic-Field Exposures from Appliances and Cancer Some appliances, such as electric blankets, constitute another exposure source that is entirely distinct from outside power lines or grounding currents. Little research has been done to address potential adverse health effects related to these devices; weakly positive results for different appliances have been reported in two studies (Savitz et al. 1990; London et al. 1991). At present, the state of knowledge on this topic can only be described as uncertain. More definitive research on this potential association would be useful given the clear documentation that exposures are incurred from at least some appliances, given the amenability of appliance use to historical recall without extensive effort on the part of the investigators, and given the independent test it provides of an effect of the magnetic fields per se.

Magnetic-Field Exposures in Schools and Other Settings Although exposures to magnetic fields outside the home, particularly in schools, have received substantial public attention, no data are available whatsoever on an association between exposures in other settings and childhood cancer. Any setting in which substantial time is spent, most notably, day-care and school, would make an important contribution to total exposure. In contrast to the potential socioeconomic confounders associated with home selection and thus with home wire codes, exposure in school is likely to be largely independent of such potential biases. Logistic challenges would be present, particularly in identifying exactly which classroom was occupied, because the fields are not likely to be homogeneous throughout a school. In addition, daytime and nighttime exposures could have different biologic effects. Nonetheless, this research gap could be addressed as another source of information to help evaluate whether magnetic fields cause cancer.

Occupational Exposures to Magnetic Fields and Adult Cancer The research exploring a link between electrical occupations and cancer, particularly leukemia and brain cancer, is extensive. (This research is discussed in detail later in the section Cancer Epidemiology—Occupational Exposures.) This research suggests a relatively small increase in risk for those workers in the aggregate, and fails



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