Static magnetic field measurements in residences in relation to resonance hypotheses of interactions between power-frequency magnetic fields and humans

Bowman et al. used epidemiologic data to test a model in which subjects wer e classified as being "in-resonance" or "not-in-resonance" for 60-Hz magnet ic-field exposures depending on single static magnetic-field measurements a t the centers of their bedrooms. A second paper by Swanson concluded that a single static magnetic-field measurement is insufficient to meaningfully c haracterize a residential environment. The main objective of this study was to investigate exposure-related questions raised by these two papers in tw o U.S. data sets, one containing single spot measurements of static magneti c fields at two locations in homes located in eight states, and the other r epeated spot measurements (seven times during the course of one year) of th e static magnetic fields at the centers of bedrooms and family rooms and on the surfaces of beds in 51 single-family homes in two metropolitan areas. Using Bowman's criterion, bedrooms were first classified as being in-resona nce or not-in-resonance based on the average of repeated measurements of th e static magnetic field measured on the bed where the presumed important ex posure actually occurred. Bedrooms were then classified a second time using single spot measurements taken at the centers of bedrooms, centers of fami ly rooms, or on the surfaces of beds, as would be done in the typical epide miologic study. The kappa statistics characterizing the degree of concordan ce between the first (on-bed averages) and second (spot measurements) metho ds of assessing resonance status were 0.44, 0.33, and 0.67, respectively. T his level of misclassification could significantly affect the results of st udies involving the determination of resonance status. (C) 2001 Wiley-Liss, Inc.