URLDate
Verified		Extra Software
Requirements
(if any)		Access
Conditions		Notes
http://dx.doi.org/10.1136/bjsm.2007.036707DOI Link
http://bjsm.bmj.com/content/41/11/733.full10/21/2014Item is within a limited-access website
http://bjsm.bmj.com/content/41/11/733.full.pdf+html10/21/2014PDF ReaderItem is within a limited-access website