ABSTRACT
RCTs have well-recognized advantages and disadvantages [6-10]. In particular, the key advantage is the minimization of both known and unknown confounders by the random allocation of individuals or groups of individuals [11,12]. Since the seminal paper by Schwartz and Lellouch, it has been common to distinguish between ef cacy trials (which tend to be explanatory) and effectiveness trials (sometimes otherwise called large simple, pragmatic, practical, or management trials) [9,13-15]. This categorical distinction has its uses, although for some purposes we may rather see ef cacy and effectiveness trials as falling along a continuum. Ef cacy trials, which usually precede effectiveness studies, refer to those conducted under more ideal, experimental conditions, while effectiveness trials are RCTs carried out in more routine clinical conditions [11,16-18]. Nevertheless, some important questions, for example, the impact of clinical guidelines, may only be researchable in real-world settings, and will therefore bypass the ef cacy study stage [19]. Cochrane has de ned effectiveness, at the patient level, as assessing whether an intervention does more good than harm when provided under usual circumstances of healthcare practice [11]. In relation to psychosocial mental health interventions within primary care, Wells has de ned effectiveness trials as those which “duplicate as closely as possible the conditions in the target practice venues to which study results will be applied” [20-22].
