Authors
Kelsh MA, Shum M, Sheppard AR, McNeely M, Kuster N, Lau E, Weidling R, Fordyce T, Kühn S, Sulser C. Measured radiofrequency exposure during various mobile-phone use scenarios. J Expo Sci Environ Epidemiol. Jun 16, 2010. Ahead of print.

Background
Most radiofrequency (RF) exposure assessments of mobile phone users for epidemiological purposes have used subscriber billing records, questionnaires, and interviews to characterize temporal features of mobile phone usage. The assumption in these methods is based on the fact that the exposure duration and measures of repetition are valid surrogates for RF energy absorbed from mobile phone handsets. However, several factors affect output power such as technical features of mobile phone handset design, the service provider technology and coverage, and other factors may have a significant impact on the intensity of RF exposure, and subsequently on the absorbed dose. This study, therefore, report quantitative measurements of mobile phone power output as a function of phone technology, environmental terrain, and handset design.

Objective
To evaluate various factors that could affect RF output such as: provider technology, environmental region (proxy for base-station density), mobile phone design, and use while moving versus use while stationary. If practical, these factors could be incorporated into future exposure assessment protocols of epidemiological studies and may be useful in the interpretation of current epidemiological research.

Methods
The RF power output level of various phones was measured under a variety of scenarios, with the expectation that these data could be translated into a measure of dose for RF exposure, the specific absorption rate (SAR). Eight different mobile phones were used. Measurements of exposures have been conducted after mobile phone use under three distinct routes (urban, suburban, and rural). Averages of peak levels and overall averages of RF power output were analyzed using analysis of variance methods.

Results
The technology was the most important factor determining the levels and variability in RF power output in the mobile phantom heads. Consistent with their technical designs, average and peak power radiated into the phantoms were highest for analog phones and lowest for CDMA phones. The study also identified the variation in RF output for GSM phones that is apparently attributable to base-station switching as reported earlier and also observed that the highest power levels were observed in rural locations and the lowest in dense urban locations.

Conclusions
The results, and epidemiological research to date, reflect primarily mobile phone exposures to the head region. Future studies of health and wireless technologies will need to factor in behavioural changes associated with the use of wireless technologies. For historical purposes, current data suggest that additional efforts to obtain information on service technology and regional variation in RF power output will improve exposure classification.


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