The editorial group responsible for this previously published document have withdrawn it from publication.
Reason for withdrawal
Authors have made no progress with this protocol in over a year due to difficulties with identifying potentially suitable studies. The protocol has been withdrawn. To view the published versions of this article, please click the 'Other versions' tab.
Sources of support
- Nottinghamshire Healthcare NHS Trust, UK.
- NHS Cochrane Collaboration Programme Grant Scheme, UK.
- German Federal Ministry of Education and Research, grant no. 01KG0812, Germany.