- Correspondence to Dr Alicja R Rudnicka, Population Health Research Institute, St George's, University of London, Cranmer Terrace, London SW17 0RE, UK;
- Received 21 August 2015
- Revised 1 December 2015
- Accepted 2 January 2016
- Published online 22 January 2016.
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- Data supplement 1 - Online supplement
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