Extremely low-frequency magnetic fields and childhood acute lymphoblastic leukemia: An exploratory analysis of alternative exposure metrics

Data collected by the National Cancer institute-Children's Cancer Group wer e utilized to explore various metrics of magnetic field levels and risk of acute lymphoblastic leukemia (ALL) in children. Cases were aged 0-14 years, were diagnosed with ALL during 1989-1993, were registered with the Childre n's Cancer Group, and resided in one home for at least 70 percent of the 5 years immediately prior to diagnosis. Controls were identified by using ran dom digit dialing and met the same residential requirements. With 30-second ("spot") measurements and components of the 24-hour measurement obtained i n the subject's bedroom, metrics evaluated included measures of central ten dency, peak exposures, threshold values, and measures of short-term tempora l variability. Measures of central tendency and the threshold measures show ed good-to-high correlation, but these metrics correlated less well with th e others. Small increases in risk (ranging from 1.02 to 1.69 for subjects i n the highest exposure category) were associated with some measures of cent ral tendency, but peak exposures, threshold values, measures of short-term variability, and spot measurements demonstrated little association with ris k of childhood ALL. In general, risk estimates were slightly higher for the nighttime (10 p.m.-6 a.m.) interval than for the corresponding 24-hour per iod.