1. UK Cochrane Centre; National Institute for Health Research Summertown Pavilion, Middle Way Oxford Oxfordshire UK OX2 7LG
2. Norwegian Knowledge Centre for Health Services; P.O. Box 7004, St. Olavs plass Oslo Norway N-0130
3. Johns Hopkins University; Center for Clinical Trials and US Cochrane Center; Bloomberg School of Public Health 615 North Wolfe Street, Mail Rm W5010 Baltimore MD USA 21205