Recruitment to randomised studies

Simplicity of study design and importance of the questions addressed Study designs that are conceptually simple, and that address questions of clinical relevance where genuine uncertainty exists, are likely to facilitate the recruitment of both investigators and participants. Also, studies with uncomplicated entry criteria are usually more attractive to investigators; those with complex eligibility criteria make recruitment more difficult, are more difficult to explain to participants, and, ultimately, their findings may have limited generalisability. Further, the enthusiasm of investigators may wane if trial protocols require substantial efforts on their part. The choice of an appropriate control arm can enhance investigator interest and comfort, particularly if the control arm reflects best clinical practice. Studies should permit changes to best clinical care during the course of study follow-up. This will maintain both the ethical integrity of the study and investigator interest, and protect participants while retaining scientific efficiency. For example, in a study examining the effects of a fibrate to prevent vascular disease in diabetes, a new indication for statin treatment, based on existing trial evidence, may emerge for some participants during follow-up. In this instance, it would be preferable to allow those participants to use statins while continuing their study medication, rather than requiring them to withdraw from the study or stop taking study medication, potentially increasing the risk of participants being lost to follow-up because statin therapy is prohibited in the study protocol. This strategy also helps maintain the relevance of the study question.