Behavioural theories, predictions, and interventions should be relevant to complex, real-world health behaviours and conditions. Habit theory and habit formation interventions show promise for predicting and promoting, respectively, longer-term behaviour change and maintenance than has been attained with theories and interventions focused only on deliberative behavioural factors. However, the concept of habit has largely been treated as uniform across different types of behaviours. In this conceptual review, we contend that the definitional aspects of habit differ at a conceptual level for simple versus more complex behaviours, with ramifications for prediction, promotion, and measurement of habits. Specifically, habits are defined as direct context-response associations learned through repeatedly rewarded responding - but what is meant by 'response' and 'reward' depends upon the complexity of the behaviour. We review literature that suggests (1) responses in complex habits have separable and substitutable components (vs a single and static, unitary component) and (2) rewards for complex habits are necessarily continued and intrinsic (vs temporary and extrinsic, respectively). We discuss some empirical and theoretical questions raised by these issues around behavioural complexity and habit. Lastly, we outline the ramifications of these issues for habit measurement (habit strength and habit formation) via self-report and objective measures.
Keywords: Habit; behaviour change; behaviour maintenance; behavioural complexity; habit formation; review.