In this viewpoint, we explore the efficacy-to-effectiveness design spectrum of randomised controlled trials that test complex interventions. We make three main arguments: 1) reporting of trial design is not always explicit in terms of the efficacy-to-effectiveness spectrum; 2) there is inconsistency between trial positioning on this spectrum and authors’ interpretations of the readiness of interventions to be implemented in real-world clinical practice; and 3) between-group effect sizes are likely to be larger in efficacy trials than effectiveness trials. We draw on five recent exemplar trials of complex interventions for low back pain published in leading medical journals and the Rating of Included Trials on the Efficacy-Effectiveness Spectrum tool to explore our assumptions. Our exploratory observations suggest inconsistency in reporting of efficacy-to-effectiveness design, and we found trends of efficacy trials having larger effects. From our observations, we make recommendations for trial end users including researchers, guideline committees and healthcare practitioners.
Quicke et al. (Mon,) studied this question.