Statistical analysis of personal radiofrequency electromagnetic field measurements with nondetects.
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 naïve 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 naïve 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 naïve 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 naïve approach. Nevertheless, estimates of source-specific medians or even lower percentiles depend on the assumed data distribution and should be considered with caution.
Röösli
Martin
M
Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland. roeoesli@ispm.unibe.ch
Frei
Patrizia
P
Mohler
Evelyn
E
Braun-Fahrländer
Charlotte
C
Bürgi
Alfred
A
Fröhlich
Jürg
J
Neubauer
Georg
G
Theis
Gaston
G
Egger
Matthias
M
D000328:Adult; D000465:Algorithms; D001822:Body Burden; D040421:Cell Phone / Q000706:statistics & numerical data*; D003430:Cross-Sectional Studies; D003627:Data Interpretation, Statistical; D004781:Environmental Exposure / Q000032:analysis*; D006801:Humans; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013557:Switzerland / Q000453:epidemiology