Meeting the challenges of implementing process evaluation within randomized controlled trials: the example of ASSIST (A Stop Smoking in Schools Trial).

It is increasingly argued that the effectiveness of health promotion interventions should be measured to inform policy and practice. The randomized controlled trial (RCT) continues to be regarded as the 'gold standard' of health services research but health promotion practitioners have raised concerns about the RCT's appropriateness for evaluating their work. A preferred model is currently the pragmatic trial, measuring effectiveness under 'routine' conditions, incorporating a process evaluation to examine context, implementation and receipt. This model was chosen by A Stop Smoking in Schools Trial (ASSIST) to evaluate an intervention in which influential Year 8 students (12-13 years old) were trained to encourage non-smoking behaviour through informal conversations with their peers. Outcome data show that the intervention was effective in reducing smoking levels in intervention schools compared with control schools. In this paper we describe the extensive process evaluation embedded within the trial and, rather than focusing on resultant data, we consider the potential for such detailed examination of process to affect the intervention's delivery, receipt and outcome evaluation. We describe how some acknowledged challenges were addressed within ASSIST, which have relevance for future similar trials: Hawthorne effects, overlapping roles within the team and distinguishing between the intervention and its evaluation.