- Correspondence to Professor Ian N M Day, School of Social and Community Medicine, University of Bristol, Oakfield House, Oakfield Grove, Bristol BS8 2BN, UK;
- Received June 26, 2015
- Revised December 4, 2015
- Accepted December 6, 2015
- First published February 1, 2016.
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- Data supplement 1 - Online supplement
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