Background
Gaps between evidence and practice pervade different healthcare systems and specialties [These research-to-practice gaps represent a strategically important problem for policy-makers, healthcare systems and research funders because they limit the health, social and economic impacts of research [There are key evaluation questions of interest to patients, professionals and policy-makers for any given implementation strategy. Does it work? For which contextual features and targeted behaviours is it likely to work? Are the costs worth the benefits?Well-conducted randomised controlled trials offer a ‘fair test’ of effectiveness by balancing known and unknown confounders so that differences in outcomes between comparison groups can be confidently attributed to intervention effects. Given that implementation strategies usually target organisations, cluster randomisation (e.g. of general practices or hospitals) is usually more appropriate than individual patient randomisation [We respond to critiques of trials for implementation science and highlight opportunities to enhance their design, delivery and efficiency. We suggest that policy-making and research communities work to optimise the conditions for conducting trials.