Exploratory trials of complex public health interventions: development of guidance for researchers and funders

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Recognition is growing of the potential public health value of interventions to improve health behaviours such as diet, physical activity and substance use. Given the complex causality of these behaviours, improving public health often requires complex interventions which comprise multiple components interacting to produce change, with their actions constrained and facilitated by their interaction with the settings into which they are introduced. Given the cost of such interventions and the potential for unintended harms, drawing on evidence of what works and rigorously evaluating effectiveness is crucial.Where feasible, randomised controlled trials (RCTs) represent the most robust means of examining effectiveness. However, complex interventions are often difficult to implement in a manner consistent with programme theory across multiple settings and target groups, whilst conducting and interpreting RCTs in real word settings is challenging. Hence, prior to committing to definitive evaluation, randomised or otherwise, attention is needed to establishing the feasibility and acceptability of intervention plans and intended evaluation designs.The need to carefully examine these issues is increasingly recognised, with an increasing number of studies describing an objective of establishing the feasibility of full scale trials. Such studies are described under terms including 'exploratory trials', 'phase 2 trials' or 'piloting and feasibility' studies. However, there is currently a lack of consistent guidance for researchers preparing bids for such work, or for peer reviewers or funders, on the most important questions to address in such studies, key methodological considerations in addressing these questions, when it is more or less appropriate to use randomisation during this phase, and the criteria on which decisions should be made regarding whether and how to progress to a full scale definitive evaluation. Hence, as reflected by the range of terms under which such studies are described, their conduct and reporting is inconsistent, and the basis on which conclusions regarding whether or not to progress to a full-scale evaluation are made often unclear.The proposed study will develop guidance for the conduct of exploratory trials through reviewing current practice and eliciting views of expert funders and researchers, beginning by using systematic review methodology to identify studies describing an intention to investigate the potential for a full scale trial (including phase 2 trials, exploratory trials or feasibility and pilot studies) and existing guidance on their conduct. We will also conduct a horizon-scanning exercise to identify recent methodological developments in the design of phase 2 trials and pilot and feasibility studies in other areas of clinical research, to ensure that the guidance learns from recent developments in these related areas.A web-based Delphi process and consensus meeting will then be used to develop guidance on when exploratory trials should be conducted, what research questions they should address, key methodological considerations in the conduct of such studies and the range of criteria that should inform a decision to proceed to a full scale definitive trial. The guidance will then be actively disseminated to research funders, researchers and journal editors to maximise its impact on the commissioning, conduct and reporting of exploratory trials of complex public health interventions.