- Correspondence to
Professor Yvonne Kelly, Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London WC1E 6BT, UK,
- Received 4 October 2012
- Revised 9 January 2013
- Accepted 29 May 2013
- Published in print 1 November 2013.
- Published online 4 October 2013.
- Published first 8 July 2013.
This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.
Files in this Data Supplement:
- Data supplement 1 - Online tables
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.