than that typically encountered in risk assessment. In terms of more accurate and precise estimates, the human data obviate the need to extrapolate from animals and, if the studies identified earlier in this report are used, extrapolation from high experimental doses to low environmental exposures is unnecessary because typical environmental exposures were used in those studies. In terms of sources of error that are not taken into account, the committee has added considerations of variation from person to person, which is controlled for genetically in animal studies; variation of dose and inaccurate measurement of dose, which are prescribed and carefully assessed in animal studies; and failure to adjust for each subject's characteristics (e.g., ethnicity or socioeconomic status) or exposure to other agents (e.g., ionizing radiation) that are known to modify the effect of exposure or directly cause the disease under study. Adjusting for these effects is not a part of traditional risk assessment, although failure to do so might result in inaccurate estimates of risk.
After reviewing the available data, the committee does not believe it is appropriate to perform a complete assessment of the risks of exposure to power-frequency electric and magnetic fields through the four formal stages described above. The committee believes that the data are too uncertain to result in a meaningful analysis. Some members of the committee considered the data so inconclusive as to preclude any attempt at risk assessment. Others believe that, even though a quantitative prediction of risk is technically possible, the interpretation of the resulting risk number would be problematic and likely lead to misinterpretations. However, many persons are concerned about the possible risks of exposure to residential electric and magnetic fields, and in light of its examination of the entire body of evidence, the committee recognizes the need to contribute to a better understanding of the risks by assessing them in a more limited context. That is attempted below. These observations might help put the risk into a context that can be considered for possible personal actions or government policies. The formal framework of risk assessment is used to the extent possible.
The conclusions presented in previous chapters concerning the possibility of risk from exposure to electric and magnetic fields are the following:
There is no evidence of effects of electric-and magnetic-field exposure on bacterial DNA. Negative results from such tests are generally accepted to imply that DNA was not damaged by the agent to which the bacterial DNA was exposed.
Cancer is generally assumed to be initiated because DNA has been damaged; therefore, findings of effects, or no effects, in this type of test might be important (subject to verification by tests in other biologic systems) in identifying an agent as hazardous.