The editorial group responsible for this previously published document have withdrawn it from publication.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 three years 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 The protocol has been withdrawn.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.
- German Federal Ministry of Education and Research, grant no. 01KG0812, Germany.
- This review has been supported by the UK NHS Cochrane Collaboration Programme Grant Scheme, UK.