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Indoor tanning and non-melanoma skin cancer: systematic review and meta-analysis

BMJ 2012; 345 doi: (Published 02 October 2012) Cite this as: BMJ 2012;345:e5909

Re: Indoor tanning and non-melanoma skin cancer: systematic review and meta-analysis

The authors report the X² test for heterogeneity was non-significant for both BCC (p=0.14) and SCC (p=0.09). This would infer that a significance level of p<0.05 has been selected, rather than p<0.1 or p<0.2, usually recommended for the test for heterogeneity because it is conservative. The reported I² statistics suggest that there is no evidence of heterogeneity, however the width of the confidence intervals indicates an imprecise estimate and therefore uncertainty about these results. Despite reporting no evidence of heterogeneity, the authors adopted a random effects model (used to limit heterogeneity) to calculate the summary statistics. The reasons for selecting this model over a fixed-effects model are not given. This made us wonder about the original studies.

A brief review showed that the original studies are less than optimum. For example: Two of the studies only included nurses as the study participants (Zhang et al. 2012; Han et al. 2006); within studies there was a lack of clarity, and across studies there was a lack of consistency about how exposure to indoor tanning was measured; the potential extent of recall bias due to various attempts to measure lifetime exposure to indoor tanning and other variables. These factors are not highlighted in the report.

This study addresses an important public health question. However, while we agree with the conclusions, some caution should be taken in assuming population effects from such a diverse and variable set of studies.

Competing interests: No competing interests

30 November 2012
Sarah A Tunnicliff
Specialty Registrar in Public Health
Yorkshire and the Humber Specialised Commissioning Group
Gawber Road, Barnsley, South Yorkshire S75 2PY