- Correspondence to Dr Frank de Vocht, School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol BS8 2PS, UK;
- Received July 17, 2015
- Revised October 15, 2015
- Accepted October 28, 2015
- First published December 16, 2015.
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- Data supplement 1 - Online supplement
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