Morrisey (2006)

Morrisey in this study used software-modified phones (SMPs) that record talk time and dynamically changing transmit power levels. He enlisted the help of Motorola employees in different sites around the world. There were 17-20 volunteers in each site, aged 20-50 years, and with similar economic status and job descriptions. These volunteers used the SMPs for 2 weeks, and the data were later analyzed. Each volunteer was sent a questionnaire within 2 weeks that included questions on their phone use. Volunteers had not known of the questionnaire during the data collection period, and so did not anticipate the need to recall information about phone use.

The author found considerable intra-individual variability in transmit power in separate calls from the same worksite, mainly arising from the phone using different base stations as the person moved around while making the call. There was also variability between individuals in the same study region. In the USA sites those in the 20-34 age group had significantly longer talk time per call than those in the 35-49 group. This was not seen in Europe and Malaysia. Averaged transmit power values from different study groups was significantly different, with USA sites having higher levels than European, with the Malaysian site being higher than the others. These differences were probably related to the fact that the USA and Malaysian sites used the 900 MHz GSM network, which has a maximal power of 250 mW, while the European sites used a mixture of 900 and 1800 MHz.  The latter has a maximal power of 125 mW. Morrisey also found that there was significant inaccuracy (45-60%) in recalling "time of use".

The author states that the transmit power data can be used to approximate human exposure to RFR, although it cannot be directly correlated with SAR levels or temperature increase. He also points out that there are many factors that can influence the relationship, such as phone position, tilt angle, phone type, and size of user head and hand. He suggests that present epidemiological studies may not have addressed the variability demonstrated in his study, and that questionnaire data on "time of use" may be seriously flawed.

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