Objectives: The output power of a mobile phone is directly related to its radiofrequency (RF) electromagnetic field strength, and may theoretically vary substantially in different networks and phone use circumstances due to power control technologies. To improve indices of RF exposure for epidemiological studies, we assessed determinants of mobile phone output power in a multinational study.
Methods: More than 500 volunteers in 12 countries used Global System for Mobile communications software-modified phones (GSM SMPs) for approximately 1 month each. The SMPs recorded date, time, and duration of each call, and the frequency band and output power at fixed sampling intervals throughout each call. Questionnaires provided information on the typical circumstances of an individual’s phone use. Linear regression models were used to analyse the influence of possible explanatory variables on the average output power and the percentage call time at maximum power for each call.
Results: Measurements of over 60 000 phone calls showed that the average output power was approximately 50% of the maximum, and that output power varied by a factor of up to 2 to 3 between study centres and network operators. Maximum power was used during a considerable proportion of call time (39% on average). Output power decreased with increasing call duration, but showed little variation in relation to reported frequency of use while in a moving vehicle or inside buildings. Higher output powers for rural compared with urban use of the SMP were observed principally in Sweden where the study covered very sparsely populated areas.
Conclusions: Average power levels are substantially higher than the minimum levels theoretically achievable in GSM networks. Exposure indices could be improved by accounting for average power levels of different telecommunications systems. There appears to be little value in gathering information on circumstances of phone use other than use in very sparsely populated regions.
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▸ An additional appendix is published online only at http://oem.bmj.com/content/vol66/issue10
Funding We acknowledge funding from the European Union Fifth Framework Program, “Quality of Life and Management of living Resources” (contract QLK4-CT-1999-01563), the International Union against Cancer (UICC), and national funding sources. The UICC received funds for this purpose from the Mobile Manufacturers’ Forum and GSM Association. Provision of funds to the Interphone study investigators via the UICC was governed by agreements that guaranteed Interphone’s complete scientific independence. These agreements are publicly available (see http://www.iarc.fr/ENG/Units/RCAd.html). Funding sources for the national software-modified phone studies included: Australia: National Health and Medical Council, Bruce Armstrong is supported by a programme grant from the University of Sydney Medical Foundation; Canada: The Canadian centers (Ottawa and Vancouver) were supported by a university-industry partnership grant from the Canadian Institutes of Health Research (CIHR), the latter including partial support from the Canadian Wireless Telecommunications Association. The CIHR university-industry partnerships programme includes provisions that ensure complete scientific independence of the investigators. DK is the NSERC/SSHRC/McLaughlin Chair in Population Health Risk Assessment at the University of Ottawa. Finland: Emil Aaltonen Foundation and Academy of Finland (grant #80921); UK: Department of Health, Contract Reference RRX51; Germany: Ministry for the Environment of the state of North Rhine-Westphalia; New Zealand: New Zealand Health Research Council.
Competing interests JW works for the research centre of France Telecom.
Ethics approval The SMP studies were approved by the IARC Ethical Review Committee and by the relevant ethical committees of the participating centres.
Provenance and Peer review Not commissioned; externally peer reviewed.