- Correspondence to Dr Mark Hamer, Department of Epidemiology and Public Health, 1-19 Torrington Place, University College London, London WC1E 6BT, UK;
- Received 15 August 2013
- Revised 16 September 2013
- Accepted 24 September 2013
- Published in print 26 October 2013.
- Published online 25 November 2013.
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