1. Choosing between randomised and non-randomised studies: a systematic review;Britton;Health Technol Assess,1998
2. Strategies to improve recruitment to randomised controlled trials;Treweek;Cochrane Database Syst Rev,2010
3. Barriers to participation in randomised controlled trials—literature summary and annotated bibliography;Ross;J Clin Epidemiol,1999
4. Strategies to improve recruitment to research studies;Mapstone;Cochrane Database Syst Rev,2007
5. Challenges in evaluating surgical innovation;Ergina;Lancet,2009