title: Temporal variability of daily personal magnetic field exposure metrics in pregnant women.
abstract: Recent epidemiology studies of power-frequency magnetic fields and reproductive health have characterized exposures using data collected from personal exposure monitors over a single day, possibly resulting in exposure misclassification due to temporal variability in daily personal magnetic field exposure metrics, but relevant data in adults are limited. We assessed the temporal variability of daily central tendency (time-weighted average, median) and peak (upper percentiles, maximum) personal magnetic field exposure metrics over 7 consecutive days in 100 pregnant women. When exposure was modeled as a continuous variable, central tendency metrics had substantial reliability, whereas peak metrics had fair (maximum) to moderate (upper percentiles) reliability. The predictive ability of a single-day metric to accurately classify participants into exposure categories based on a weeklong metric depended on the selected exposure threshold, with sensitivity decreasing with increasing exposure threshold. Consistent with the continuous measures analysis, sensitivity was higher for central tendency metrics than for peak metrics. If there is interest in peak metrics, more than 1 day of measurement is needed over the window of disease susceptibility to minimize measurement error, but 1 day may be sufficient for central tendency metrics.
authors.affiliation: University of Michigan School of Public Health, Department of Environmental Health Sciences, Ann Arbor, Michigan, USA.
authors.forename: Ryan C
authors.initials: RC
authors.lastname: Lewis
authors.affiliation: University of North Carolina Gillings School of Global Public Health, Department of Epidemiology, Chapel Hill, North Carolina, USA.
authors.forename: Kelly R
authors.initials: KR
authors.lastname: Evenson
authors.affiliation: Brown University School of Public Health, Department of Epidemiology, Providence, Rhode Island, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Savitz
authors.affiliation: University of Michigan School of Public Health, Department of Environmental Health Sciences, Ann Arbor, Michigan, USA.
authors.forename: John D
authors.initials: JD
authors.lastname: Meeker
mesh_terms: D061725:Accelerometry; D056044:Actigraphy; D000328:Adult; D004781:Environmental Exposure / Q000009:adverse effects / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D060526:Magnetic Fields / Q000009:adverse effects; D009043:Motor Activity; D011247:Pregnancy; D012680:Sensitivity and Specificity; D013997:Time Factors