and cancer studies concerns exposure assessment. The evolution of cancer epidemiology studies has progressed far more, however, than reproductive studies because refinements are being made successively in the studies. At least one major reproductive study is in progress at the California Department of Health Services directed by Dr. Shanna Swan. The study in progress and recently completed ones use the most sophisticated exposure assessment methods available to investigate spontaneous abortion, late fetal loss, fetal-growth retardation, and preterm delivery. Given the relatively short time course of pregnancy and the relatively high frequency of some adverse outcomes, the opportunity to monitor exposure prospectively or at least closer in time to the development of reproductive effects is much greater than that for cancer. The newer studies include home measurements as well as reports of appliance use and measurements. Given how limited previous studies of reproductive effects have been, these new results could completely change the picture in ways that cannot be predicted.
Confounding is a somewhat greater concern for reproductive health outcomes than for childhood cancer, largely because so much more is known about risk factors. Across many reproductive outcomes (with the exception of many congenital malformations), there are strong associations with social class, mother's age, tobacco use, and, to a lesser extent, alcohol and illicit drug use. The more sophisticated studies take such factors into account, and failure to do so could easily lead to confounding of such sources of electric-and magnetic-field exposures as electric blankets or residence in high-exposure homes.
Selection bias is a concern here as well, but the source population can be defined unambiguously with greater ease from birth records or prenatal care records. Potential for recall bias and response bias are also relevant to interpreting reproductive studies, particularly because such exposures as electric blankets are increasingly perceived by the public as potentially harmful. These perceptions could affect reporting by women who have had an adverse outcome (recall bias) or affect their willingness to participate in the study at all (response bias).
The scientific literature on the association between exposure to power-frequency electric and magnetic fields and behavior includes a series of studies that relate exposure to a wide range of outcomes, including suicides, depressive symptoms, headaches, and neuropsychologic performance. In general, the studies of behavioral outcomes used potentially biased designs and obtained results that are inconsistent and of poor quality. Few studies used a validated measurement instrument to assess subjective symptoms, opportunity for misclassification of exposure and outcome was ample, most did not adjust adequately for confounding (especially demographics), and few used expsoure measurements with adequate temporal and spatial resolution. Nonetheless, the consistent lack of association seen in this set of studies is notable. The committee reviewed the details of these