Redmayne M, Inyang I, Dimitriadis C, Benke G, Abramson MJ. (2010). Cordless telephone use: implications for mobile phone research. J Environ Monit. 12(4):809-12.

In the last 10 years, the use of mobile phones has increased substantially, and cordless phones have become normal household appliances. While mobile phones have been the focus of most epidemiological research on possible health effects, cordless phones have not received that much attention. However, exposure from cordless phone bases and handsets can make a considerable contribution to total RF exposure from telephones. For epidemiologists, it is important to find out whether treating those with only cordless phones as unexposed can bias the association between wireless phone use and studied health outcomes. It is also important to know if there is a correlation between mobile and cordless phone use. If a positive correlation exists, the difference in the level of RF exposure between high mobile phone users and low mobile phone users would increase.

The objective of this study was to assess the proportion of adolescents with cordless telephones at home, among them - the proportion of those who did not own a mobile phone, and whether or not cordless phone use was correlated with mobile phone use in a sample of secondary school students.

The sample included 12-13 year old students from 13 government, 4 Catholic and 3 independent secondary schools in Melbourne, Australia. The number of schools represents the proportion of students attending each school sector. Questionnaires were completed by the participants and their parents. Exposures to mobile and cordless phones were assessed with a modified version of the questionnaire used in the INTERPHONE study.

Of 479 students who were invited to participate, 317 students agreed (participation rate 66%). Of the 317 participants; 46% were boys and 54% girls. Eighty seven percent had a cordless phone at home, 77% owned and 80% used a mobile phone. A total of 97% (307 of the 317) had access to one or the other type of telephone. Of the 74 children who did not own a mobile phone, 62 (84%) reported having a cordless phone at home. Twenty two of them (33%) used it more than the median level of the entire group. Ten children (3%) of those who had a cordless phone at home did not use it. The reported total number of calls on cordless phones was slightly lower than the number of calls on mobile phones; the Pearson correlation between these two numbers was 0.38 (p<0.01).

The results of this study are in agreement with the results of two Swedish studies, one of which reported a similar proportion of high school students having a cordless phone at home and the other – a positive association between mobile and cordless phone use. The phone use in the second study was estimated in terms of call duration, so its results are not directly comparable to the results of the present study. The positive correlation between the uses of the two types of wireless telephones alters the ratio of RF exposure between high and low mobile phone users. The finding that 33% of mobile phone non-users use a cordless phone at a level above-average implies that there may be a confounding in mobile phone studies that do not account for cordless phone use.

The authors concluded that “when designing and analyzing epidemiological mobile phone studies, it is important to also assess cordless phone handset and base exposure in order to accurately evaluate total RF telephone exposure effects”.

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