Authors’ reply to Kundi and Davis and colleaguesBMJ 2012; 344 doi: http://dx.doi.org/10.1136/bmj.e3088 (Published 01 May 2012) Cite this as: BMJ 2012;344:e3088
- M P Little, senior scientist1,
- P Rajaraman, investigator1,
- R E Curtis, research statistician1,
- S S Devesa, contractor1,
- P D Inskip, senior investigator1,
- D P Check, programmer1,
- M S Linet, senior investigator1
We clearly state in the statistical methods that, while the figures are based on a specific reference group (men aged 60-64, Los Angeles registry), the entire dataset was used to estimate these rates.1 2 3 The reference group was chosen purely for statistical reasons, to minimise the variance of estimates: choosing a different group would make little difference to inference on trends. We also show projected rates in appendix tables A5-A10 for all relevant age, sex, and ethnic groups, and the results shown in the figures broadly support results for the whole study population.
We agree with Kundi that it cannot be assumed that the proportions of mobile phone use are the same for all US population subgroups.2 However, the projected rates for 2008 are heavily dominated by risk for those first using phones in the most recent five years (the first term in formula A2), when US usage approached 100%; over 95% of the 44.7% excess relative risk predicted for the US population by the study of Hardell et al comes from this group,5 so heterogeneity in patterns of phone use would have little impact. As we state in the paper,1 glioma risks observed in the US population are consistent with the doubled risks in the small proportion of heavy users predicted by the INTERPHONE study.6 Our study does not provide confirmatory evidence of a 1.5 to twofold increase in glioma risk with regular use over a decade, as stated by Davis and colleagues.3
Cite this as: BMJ 2012;344:e3088
Competing interests: None declared.