Updated study contains poor science and should be disregarded
This update has failed to control for a number of flaws and omissions that severely detracted from the quality of data in the previous paper, published in 2006 .
The first flaw in the paper is the ability to correctly identify the mobile phone subscribers between 1987 and 1995. 620,602 early subscribers were validated in their original data set. 200,507 were corporate users whose names were unknown and were excluded, leaving 420,095 'early users'. This update has excluded another 61,692 of the 'early users' resulting in a participation rate of only 58% of identified early subscribers. All of the remaining 42% will be placed in the "non-user" category (the majority of which, by the author's own admissions, will be likely to be the heaviest user group in the data set).
Even for the remaining 58% of identified subscribers, no information was collected pertaining to actual mobile phone usage, using "number of subscription years" as a surrogate. Not only does the paper contain no data on mobile phone subscribers since 1995, it has absolutely no information about actual exposure - despite frequently using the term 'exposure' in the paper. In the 2011 update on the carcinogenicity of radiofrequency electromagnetic fields, the 30 scientist IARC monograph panel were quite critical of the failings in the original paper: "In this study, reliance on subscription to a mobile phone provider, as a surrogate for mobile phone use, could have resulted in considerable misclassification in exposure assessment." 
An even more damaging limitation is the exposure classification in the "non-subscriber" part of the cohort, which has been analysed as if it is a group of individuals with no mobile phone exposure. On top of containing the 42% from the originally identified dataset, the proportion of the Danish population that held a mobile phone subscription increased from 10% to 95% between 1995 and 2004. This not only means that a significant majority of the non-subscriber category will be mobile phone users, but many of whom will have used their phone for over 10 years, despite being classified in the study as "non-users". The magnitute of this confounder makes meaningful comparisons in the data impossible.
Finally, the authors made no effort to control for any other forms of RF exposure. The primary author (Frei) has previously demonstrated that about only about 30% of adult microwave exposure now comes from their mobile phone handset use , with approximately 30% from cordless phones, 30% base stations and 10% other sources. These other exposures could be highly relevant, as Lennart Hardell has repeatedly shown increases in brain tumours associated with extensive cordless phone use , a technology that has been in widespread use since 1995.
It is unclear how this latest paper makes any novel contributions to the existing literature on mobile phones and brain tumours, as it contains significantly worse flaws than either the INTERPHONE group's research or the papers published by Lennart Hardell. The magnitude of the limitations in this research make meaningful analyses and conclusions virtually impossible.
It is also unclear how this study is meant to help doctors and other health professionals make better decisions that will improve outcomes for patients as stated in BMJ's publication mission statement .
Alasdair Philips and Graham Lamburn
1. Schuz J, et al. (2006) Cellular telephone use and cancer risk: update of a nationwide Danish cohort. JNCI 2006. 98:1707-13.
2. WHO IARC Monograph Working Group, Carcinogenicity of radiofrequency electromagnetic fields. Lancet Oncol. 2011 Jul;12(7):624-6.
3. Frei P, et al, (2010) Classification of personal exposure to radio frequency electromagnetic fields (RF-EMF) for epidemiological research: Evaluation of different exposure assessment methods., Environ Int 2010 Oct;36(7):714-20
4. Hardell L, Carlberg M, Hansson Mild K. (2011) Pooled analysis of case-control studies on malignant brain tumours and the use of mobile and cordless phones including living and deceased subjects. Int J Oncol. 2011 May;38(5):1465-74. doi: 10.3892/ijo.2011.947. Epub 2011 Feb 17.
5. BMJ website. What does the BMJ publish?
Competing interests: We are both involved in running Powerwatch, a small UK NGO active in the field of EMF exposure and health since 1987. We currently advise a precautionary approach to mobile phone use, especially by children.