The wilful rejection of psychological and behavioural interventions

Psychology and behavioural science play a key role in the development, testing, and implementation of interventions aimed at addressing societal challenges. Some of these interventions have been impactful in shaping policy decisions, but their successful real-world implementation is beset by challenges, including a large number of people who might benefit from an intervention choosing to ignore it. However, there is almost no research on why people wilfully reject participating in an intervention: they notice it, consider participation, and decide against it. Addressing this knowledge gap is of critical importance for improving intervention uptake. Drawing on the literature on wilful ignorance, we propose a Bayesian model of the wilful rejection of psychological and behavioural interventions. People's prior beliefs about the relevance of an intervention, its effectiveness, and the goals and reliability of the intervention's source, strongly inform the probability of people wilfully rejecting an intervention when they come across it. Based on this model, we argue that people may downgrade their perceptions of the source's reliability if they perceive the intervention itself to be inefficacious, and that using intervention sources with high perceived reliability among target audiences is key to optimising intervention uptake.