URLDate
Verified		Extra Software
Requirements
(if any)		Access
Conditions		Notes
http://dx.doi.org/10.1136/bjsm.2006.027623DOI Link
http://bjsm.bmj.com/content/40/12/975.full.pdf 05/13/2014 PDF Reader
http://bjsm.bmj.com/content/40/12/975.full 05/13/2014