Sampling Design and Field Methods of a Large, Randomized, Multisite Survey of Occupational Magnetic Field Exposure

Abstract Large, randomized assessments of occupational exposure remain unusual in epidemiologic studies because of logistical barriers. Our study of workers in five U.S. electric companies requires estimates of full-shift time-weighted average (TWA) magnetic field exposure for 28 job groups, with the ability to separate within-worker and between-worker variability. Valid exposure assessment for this study is challenging because workers are dispersed over wide geographic areas. We used an innovative random monitoring strategy that may be useful in future studies. A target sample size of 4000 measurements was chosen based on considerations of precision and feasibility. Jobs were aggregated into three levels of presumed exposure. The number of measurements for each job was weighted such that the presumed medium-exposure and high-exposure groups were respectively sampled with three and five times the frequency of the low-exposure group, and measurements were distributed within these levels in proportion to th...