Journal Article Key references Get access J Jefferson J Jefferson Senior Research Fellow, Collaborating Centre for Health Services Research, Nuffield Institute for Health71–75 Clarendon Road, Leeds LS2 9PL, UK Search for other works by this author on: Oxford Academic PubMed Google Scholar British Medical Bulletin, Volume 51, Issue 4, 1995, Pages 949–958, https://doi.org/10.1093/oxfordjournals.bmb.a073008 Published: 01 December 1995