- Received 27 November 2012
- Revised 30 April 2013
- Accepted 30 April 2013
- Published in print 1 June 2013.
- Published online 6 June 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