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Public health evaluation: which designs work, for whom and under what circumstances?
  1. Laurence Moore,
  2. Graham F Moore
  1. Cardiff Institute of Society and Health, Cardiff University School of Social Sciences, Cardiff, UK
  1. Correspondence to Laurence Moore, Professor of Public Health Improvement, Cardiff Institute of Society and Health, Cardiff University School of Social Sciences, 1-3, Museum Place, Cardiff CF10 3BD, UK; moorel1{at}

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Properly designed and conducted randomised controlled trials (RCTs) represent the most internally valid means of estimating the effectiveness of complex interventions.1 However, RCTs are often dismissed as being unsuitable for the evaluation of public health interventions, in a debate often dominated by arguments based on misunderstandings, misrepresentations and ideological objections. Macintyre2 counters many of these arguments and argues that ‘RCTs are both more possible than many objectors think, and more conclusive about the benefits and cost effectiveness of policies and interventions [than other designs]’.

The paper by Bonell and colleagues (see page 582)3 and its companion paper by Cousens and colleagues (see page 576)4 provide welcome contributions to this debate, by seeking to delineate circumstances in which RCTs may not be possible and describing various analytical approaches to compensate for the lack of randomisation in order to derive unbiased estimates of effect. Bonell et al3 identify three key features of RCTs, random allocation, control groups and prospective follow-up, of which only the first is unique to RCTs.

To randomise or not to randomise? For whom and under what circumstances is randomisation acceptable and feasible?

The ethical case for randomisation centres around the existence of equipoise, or uncertainty regarding intervention effects. Indeed, given that untested interventions may be costly and unexpectedly harmful, it is unethical to invest in interventions without testing them. However, as argued by Bonell and colleagues, widespread belief by policy makers and practitioners in the effectiveness of public health interventions, coupled with often erroneous assumptions that they are unlikely to cause harm, commonly leads to perceptions that it is unethical to ‘withhold’ intervention from some participants, and therefore a resistance to randomise allocation. While Bonell and colleagues identify this reluctance as a problem and identify particular circumstances where reluctance may be greater, they do not describe strategies to overcome this problem, and in the process help researchers act …

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  • Linked articles 082610, 082602.

  • Competing interests None.

  • Provenance and peer review Commissioned; not externally peer reviewed.

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