Statistical analysis of personal radiofrequency electromagnetic field measurements with nondetects.
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Date
2008-08-11
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Abstract
Exposimeters are increasingly applied in bioelectromagnetic research to determine personal radiofrequency electromagnetic field RF EMF exposure The main advantages of exposimeter measurements are their convenient handling for study participants and the large amount of personal exposure data which can be obtained for several RF EMF sources However the large proportion of measurements below the detection limit is a challenge for data analysis With the robust ROS regression on order statistics method summary statistics can be calculated by fitting an assumed distribution to the observed data We used a preliminary sample of 109 weekly exposimeter measurements from the QUALIFEX study to compare summary statistics computed by robust ROS with a na ve approach where values below the detection limit were replaced by the value of the detection limit For the total RF EMF exposure differences between the na ve approach and the robust ROS were moderate for the 90th percentile and the arithmetic mean However exposure contributions from minor RF EMF sources were considerably overestimated with the na ve approach This results in an underestimation of the exposure range in the population which may bias the evaluation of potential exposure response associations We conclude from our analyses that summary statistics of exposimeter data calculated by robust ROS are more reliable and more informative than estimates based on a na ve approach Nevertheless estimates of source specific medians or even lower percentiles depend on the assumed data distribution and should be considered with caution