Updated study contains poor science and should be disregardedBMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d7899 (Published 06 December 2011) Cite this as: BMJ 2011;343:d7899
The update of the Danish cohort study of mobile phone use and cancer risk has the serious flaws present in the original publication.1 2 The first flaw in the update is the correct identification of mobile phone subscribers between 1987 and 1995. This resulted in a participation rate of only 58% of identified early subscribers, with the remaining 42% placed in the “non-exposed” category (which, by the authors’ own admission, could well be the heaviest user group in the dataset).
Even for the identified subscribers, no information was collected pertaining to actual mobile phone usage. “Number of subscription years” was used as a surrogate, which the IARC monograph panel said could result in “considerable exposure misclassification” earlier in 2011.3 The paper contains no data on mobile phone subscribers since 1995 and no information about actual exposure.
An even more damaging limitation is the exposure classification in the “non-subscriber” part of the cohort, which has been analysed as having no exposure to mobile phones. The proportion of the Danish population with a mobile phone subscription increased from 10% to 95% between 1995 and 2004 (from which the “non-exposed” group are drawn), many of whom will have used their phone for over 10 years. The size of this confounder makes meaningful comparisons in the data impossible.
Finally, the authors made no effort to control for any other forms of radio frequency exposure. Frei et al previously showed that only about 30% of adult microwave exposure currently comes from use of mobile phone handsets,4 with around 30% from cordless phones and 40% from far field sources. This could be highly relevant because Hardell et al have shown increases in brain tumours associated with use of cordless phones,5 which have been in widespread use since 1995.
Cite this as: BMJ 2011;343:d7899
Competing interests: AP and GL are both involved in running Powerwatch, a small UK non-governmental organisation active in electromagnetic field exposure and health since 1987. They currently advise a precautionary approach to mobile phone use, especially in children.