characterizing home exposure (integration over time and consideration of grounding currents) with complete coverage of cases and controls could yield important insights into the possibility that magnetic fields account for the wire-code and cancer association.
Evidence that sources of fields other than those from power lines are related to childhood cancer would provide convergent evidence and strongly bolster the hypothesis that it is actually the magnetic fields associated with wire codes that influence childhood cancer risk. Other sources of exposure to electric and magnetic fields in the home, such as appliances, or sources outside the home, such as those encountered in schools, could have different potential confounders and other methodologic issues, and observed associations would be unlikely to suffer from the same validity concerns as the associations of power lines and cancer in previous studies.
Both epidemiologic and biologic studies rely on an accurate determination of the exposure variables. Characterization of the environmental fields provides a basis to test associations of epidemiologic variables with the measured field parameters and provides information on relevant features of the fields for use in biologic studies. Additional refinements in engineering techniques and in field characterization could be considered an integral part of any research agenda.
Instrumentation is needed that can measure more rapid changes in magnetic-field strength (changes on the order of 0.1 sec). Currently, instrumentation can capture a sample of the magnetic field every few seconds, but in biologic experiments, cells can respond to more rapid changes. For example, the ear can distinguish events that are separated by more than about 0.1 sec; it fuses events that occur more rapidly. The ability to measure magnetic-field change on the order of 0.1 sec could be used to test some of the more recent hypotheses of magnetic-field interactions. In addition, before epidemiologic or laboratory studies can be designed to test hypotheses involving transient currents, a standard way to produce and measure transient currents must be developed.