Practical parsimony and complexity in conceptualising habit.

Our ultimate goal, as health psychologists, is to help individuals be healthier – specifically, through changing behaviour and maintaining those changes. Health psychologists are interested in habits, because they hold promise for facilitating behavioural maintenance through automatic processes (Gardner, 2015; Kwasnicka et al., 2016). How we conceptualise habit has ramifications for how we promote (intervene in) and measure habit formation and maintenance. In Phillips and Mullan (2022), we offered a conceptual review of the literature, evaluating the impact of behavioural complexity on the conceptualisation of habit, using a definition of habit defined in the literature (Wood et al., 2022) as ‘direct context-response associations learned through repeatedly rewarded responding’ (p. 12). Specifically, we argued that complex behaviours (determined by their relatively greater number of preparatory and enactment steps and amount of time to prepare and enact, compared to simpler behaviours): (1) have meaningfully separable ‘responses’ that may be habitual (e.g., in their instigation vs execution or with substitutable, ‘lower order’ actions, which may themselves be habitual) and (2) rely on intrinsic rewards (versus extrinsic) for habit formation and maintenance. In response to Phillips and Mullan (2022), Gardner and Lally (2022) and Rebar et al. (2022) offer thought-provoking and valuable insights regarding these points. On the surface, these sets of authors seemingly have opposing views on advancing the topic of complex health behaviours and habit: Gardner and Lally (2022) argue for greater parsimony in habit conceptualisation for simple and complex behaviours, whereas Rebar et al. (2022) argue for even greater complexity in our conceptualisation and measurement of complex health behaviours and habits. However, we articulate in this commentary how there is much agreement, as well as room for continued debate, among these viewpoints and those in Phillips and Mullan (2022). In sum, we argue in this commentary for a practical approach to habit research for complex behaviours that is both parsimonious and appropriately complex. We contend, as do Gardner and Lally (2022), that our definition and conceptualisation of habit should be useful – useful for achieving our ultimate goal, which is to help individuals change their behaviour and to maintain behaviour changes for optimal health.