How are habits formed: Modelling habit formation in the real worldy

To investigate the process of habit formation in everyday life, 96 volunteers chose an eating, drinking or activity behaviour to carry out daily in the same context (for example ‘after breakfast’) for 12 weeks. They completed the self-report habit index (SRHI) each day and recorded whether they carried out the behaviour. The majority (82) of participants provided sufficient data for analysis, and increases in automaticity (calculated with a sub-set of SRHI items) were examined over the study period. Nonlinear regressions fitted an asymptotic curve to each individual’s automaticity scores over the 84 days. The model fitted for 62 individuals, of whom 39 showed a good fit. Performing the behaviour more consistently was associated with better model fit. The time it took participants to reach 95% of their asymptote of automaticity ranged from 18 to 254 days; indicating considerable variation in how long it takes people to reach their limit of automaticity and highlighting that it can take a very long time. Missing one opportunity to perform the behaviour did not materially affect the habit formation process. With repetition of a behaviour in a consistent context, automaticity increases following an asymptotic curve which can be modelled at the individual level. Copyright # 2009 John Wiley & Sons, Ltd. Performing an action for the first time requires planning, even if plans are formed only moments before the action is performed, and attention. As behaviours are repeated in consistent settings they then begin to proceed more efficiently and with less thought as control of the behaviour transfers to cues in the environment that activate an automatic response: a habit. How long does it take to form a habit? This question is often asked by individuals who want to acquire healthy habits or those who want to promote behaviour change. However, we are not aware of any studies that have systematically investigated the habit formation process within individuals, and none have examined the development of ‘real world’ habitual behaviours. The past decade has seen a resurgence of interest in the topic of habitual behaviour within social psychology. There is still debate over how habits should be conceptualized and operationalized, but there is consensus that habits are acquired through incremental strengthening of the association between a situation (cue) and an action, i.e. repetition of a behaviour in a consistent context progressively increases the automaticity with which the behaviour is performed when the situation is encountered (Verplanken, 2006; Wood & Neal, 2007). ‘Automaticity’ is evidenced by the behaviour displaying some or all of the following features: efficiency, lack of awareness, unintentionality and uncontrollability (Bargh, 1994). Historically, habit has been measured by assessing the frequency of past behaviour (Sheeran, 2002; Ajzen, 2002). However, this assumes that the relationship between repetition and automaticity is linear, which is unlikely because it implies that every repetition, whether early on in the habit formation process or after a large number of repetitions, would result in the same increase in automaticity. More plausibly, a behaviour becomes as automatic as it can get after some European Journal of Social Psychology Eur. J. Soc. Psychol. 40, 998–1009 (2010) Published online 16 July 2009 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/ejsp.674 *Correspondence to: Phillippa Lally, Cancer Research UK Health Behaviour Research Centre, Department of Epidemiology and Public Health, University College London, Gower Street, London, WC1E 6BT, UK. E-mail: [email protected] yThis research was conducted by Phillippa Lally when she held aMedical Research Council PhD studentship and has been written up during an Economic and Social Research Council postdoctoral fellowship. Copyright # 2009 John Wiley & Sons, Ltd. Received 5 June 2009 Accepted 12 June 2009 number of repetitions, and further repetition no longer increases automaticity. In addition, early repetitions could be expected to result in larger increases as the association between situation and action is created. Hull’s early work (1943, 1951) suggested that the relationship between repetition and habit strength follows an asymptotic curve in which automaticity increases steadily—but by a smaller amount with each repetition—until it reaches an asymptote (plateau). This idea was based on laboratory data from human and animal studies where habit strength was inferred from behavioural responses (e.g. drops of saliva secreted in response to a cue) rather than the subjective experience of automaticity. However, because outcomes were averaged across groups, it was not clear whether the curve applied at an individual level. The exact nature of the relationship between repetition and automaticity, and the time it takes for habit acquisition to occur, have been relatively unexplored because the recent literature has focused largely on established habits rather than the process of habit development. There is a clear need to extend Hull’s work by examining individual responses and real-world behaviours. This idiographic approach allows conclusions about the general process of habit formation to be drawn from examination of the process across individuals. THE PRESENT RESEARCH The aim of the present study was to investigate the development of automaticity in a series of volunteers whowere asked to repeat a behaviour of their choice, in response to a cue, in an everyday setting, and complete a measure of automaticity on a daily basis. As described above, it is generally agreed that repeating a behaviour in a consistent situation allows cueresponse links to be formed.We therefore tried to control context stability by asking participants to carry out the behaviour in the same situation each day. We selected situations rather than times as cues, because prospective memory research indicates that situations permit external cueing of an intended action whereas time cues require monitoring to identify the time to act (McDaniel & Einstein, 2000). We used daily automaticity scores as the outcome to model increases in automaticity over time within individuals, and assess the time taken for each participant to reach their maximum automaticity. The role of reinforcement/rewards in habit development and maintenance is unclear. In the behaviourist tradition, habit strength has been considered to be a function of repetition only when rewards are received for performing the behaviour upon encountering a cue (Hull, 1943, 1951); without reinforcement there can be no habits. However, it is unclear whether external rewards need to be provided after each repetition if the behaviour is inherently rewarding. In the present study, participants chose behaviours they wanted to perform; we assumed these to be intrinsically rewarding and no extrinsic rewards were given for performing the behaviour. In the habit literature, three different methods have been used to quantify habit strength in humans, although they have predominantly been used to characterize existing behaviours as habitual or not, rather than to examine the process of habit acquisition. The response frequency measure (RFM) (Verplanken, Aarts, van Knippenberg, & van Knippenberg, 1994) assesses generalized habits across different situations (e.g. car use when travelling to different locations) and so is not applicable to assessing change in a specific behaviour in a specific situation. A second approach (Wood, Quinn, & Kashy, 2002; Wood, Tam, &Witt, 2005) is derived from multiplying ratings of the frequency of performance of the behaviour by the consistency of performance context. Because this is based on an assessment of behavioural frequency, it does not lend itself to tracking habit formation in response to deliberate daily repetition. The third measure is the self-report habit index (SRHI) (Verplanken & Orbell, 2003), which assesses a respondent’s subjective experience of several features of habits, three of which are seen as central to automaticity (lack of awareness, lack of control and efficiency), along with two others (history of repetition and identity), in a 12-item questionnaire. The SRHI has been shown to have good test–retest reliability, to correlate well with the RFM and past behaviour measures, and can differentiate between behaviours that are performed with different frequencies (Verplanken & Orbell, 2003). The SRHI has discriminant validity over and above past frequency of behaviour in predicting future behaviour. It has also been used to show that for the same number of repetitions a simple behaviour has a higher habit score than a complex behaviour (Verplanken, 2006). Habit strength measured using the SRHI (or a subset of SRHI items) has been shown to be associated with various eating behaviours including snacking and fruit and vegetable consumption in adults, and sugar-sweetened beverage consumption in adolescents (Brug, de Vet, de Nooijer, & Verplanken, 2006; Verplanken & Orbell, 2003; Kremers, van der Horst, & Brug, 2007; Verplanken, 2006; Reinaerts, de Nooijer, Candel, & de Vries, 2007; de Bruijn, Kremers, de Vet, de Copyright # 2009 John Wiley & Sons, Ltd. Eur. J. Soc. Psychol. 40, 998–1009 (2010) DOI: 10.1002/ejsp Habit formation 999