MAGNETIC-FIELD EXPOSURE ASSESSMENT IN A CASE-CONTROL STUDY OF CHILDHOOD LEUKEMIA

Epidemiologic evaluation of the relation between magnetic field exposu res and cancer depends critically on study design, particularly the me thods used for exposure assessment. We incorporated a complex magnetic field exposure assessment protocol into a large incident case-control study of childhood leukemia. We measured residential magnetic fields using a standard protocol in current and former homes of 638 cases and 620 controls and determined wire codes for 414 case-control pairs. We chose a time-weighted average of magnetic field measurements in each eligible home, weighted by the time the subject lived in each home as the main exposure metric for each subject. We found that 24-hour bedro om magnetic field measurements adequately characterize children's resi dential exposure and that measuring other rooms contributes only sligh tly to the estimate of average residential exposure to magnetic fields . Front door measured fields provide useful exposure information when interior measurements are missing. If feasible, measuring multiple hom es in which the subject has resided is preferable to measuring a singl e home. A similar distribution of wire codes for controls agreeing or refusing to participate in our study implies that risk estimates deriv ed from wire code data will not be influenced by response bias.