Process evaluations are studies which try to understand how complex health behaviour and health care interventions operate to produce their outcomes. They are increasingly conducted alongside randomised controlled trials (RCTs), complementing the ‘does this work’ question of the trial with ‘how does it work?’ questions. Process evaluations examine factors such as how interventions are implemented, how participants respond to interventions and change their behaviour (or not), and contextual factors which affect different stages of the intervention. They are usually theory-based, meaning the study design is based on the theory of how the intervention is thought to work; the theory is tested by the study but may also be developed or changed if unexpected findings occur. Process evaluations also typically use mixed methods (using qualitative and quantitative data) to answer a set of related research questions about how the intervention works.
“Process evaluation – a study which aims to understand the functioning of an intervention, by examining implementation, mechanisms of impact, and contextual factors. Process evaluation is complementary to, but not a substitute for, high quality outcomes evaluation.” (Moore G, Audrey S, Barker M, Bond L, Bonell C, Hardeman W, Moore L, O’Cathain A, Tinati T, Wight D, Baird J. 2014. Process evaluation of complex interventions: Medical Research Council guidance. MRC Population Health Science Research Network, London)