The COM-B model of behaviour change suggests that to engage in a behaviour (B), a person needs to have the capability (C), opportunity (O) and motivation (M) to perform that behaviour, so any behaviour change will require modifying at least one of those components [1].

In the context of COM-B, capability refers to a person’s psychological and physical ability to engage in a behaviour. Psychological capability includes having the necessary knowledge to perform a behaviour but also the necessary mental skills, such as attention, memory or decision-making skills. Physical capability refers to bodily functions, such as having the strength, stamina or dexterity needed to perform a behaviour.

Opportunity refers to the external factors – physical and social – that enable the behaviour. Physical opportunity refers to the environment where the behaviour takes place, but also to physical resources such as money or time. Social opportunity involves the behaviour of significant others and of our broader social networks. Motivation involves all the internal processes that trigger or inhibit a behaviour, and that ultimately result in us performing a particular behaviour instead of any other possible competing behaviour. These processes can be reflective, involving plans, beliefs, attitudes, or goals, and automatic, involving emotions and habits that may not enter conscious awareness. 

The COM-B components interact through positive and negative feedback loops, creating dynamic systems of behaviour. For example, a person following a well-designed running programme will be (and feel) more capable to run and, in turn, this might make this person want to run more, positively impacting their motivation. However, if someone lives in an area that isn’t well lit and where there are no safe tracks for runners, their motivation to run might decrease. 

Understanding the factors that influence behaviour is key to identifying barriers to behaviour change and COM-B allows you to diagnose barriers to behaviour change. However, if we need an even more detailed understanding of the behaviour we’re trying to change, we can further build on COM-B with the Theoretical Domains Framework (TDF). The TDF consists of 14 detailed domains essential for behaviour change, which link to the different COM-B components to add an extra layer of insight. For example, within the psychological capability component, the TDF identifies 4 relevant domains: knowledge, cognitive skills, memory, attention and decision processes and behavioural regulation [2].

Once we have diagnosed the barriers to behaviour, either at the basic (COM-B) or advanced level of detail and complexity (TDF), we can combine these insights with the Behaviour Change Wheel (BCW), which links each COM-B component to intervention functions that are likely to influence them according to evidence. The BCW also helps you identify types of policy that can be used to effectively deliver these interventions [3]. For example, if we had to address barriers in reflective motivation, educatio, persuasion, incentivisation or coercion could be useful. Within the ecosystem of tools that comes with COM-B, there is also a comprehensive taxonomy of Behaviour Change Techniques (BCTs) that can be leveraged to specify the contents within an intervention. BCTs are the ‘active psychological ingredients’ of an intervention, which can be used in isolation or in combination with other BCTs to change behaviour. For example, if we intend to influence reflective motivation through the use of persuasion, we might find that increasing the salience of the consequences of doing the behaviour is useful (e.g. telling a story about a young mother who died - consequences - after being run over by a drunk driver - behaviour to change -. 

When we put together all the tools that come with COM-B, we get a robust and actionable model that builds on complexity progressively, to go from diagnosis to intervention design, policy category and implementation content. 

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COM-B tip 

Categorising barriers to behaviour in terms of capability (physical or psychological), opportunity (physical or social) and motivation (reflective or automatic) gets easier with practice. To help you navigate the model, you can ask yourself these questions: 

Physical capability

Do people need to overcome physical limitations to do the behaviour?

Do people have the physical skills needed (dexterity, strength, eyesight…)

Psychological capability

Do people need to know more about the behaviour?

Do the people need to understand why the behaviour is important?

Do people need to overcome mental obstacles?

Do people need to pay attention to do the behaviour?

Do people find the behaviour easy to do?

Physical opportunity

Do people have the time to do the behaviour?

Do people have the financial resources to do the behaviour?

Do people need special tools to do the behaviour?

Are there triggers in the environment to prompt the behaviour?

Social opportunity

Do people have the social support required to do the behaviour?

Do other people encourage or discourage the behaviour?

Do other people behave in a similar way?

Reflective motivation

Do people feel like they want or need to do the behaviour?

Do people care about the consequences?

Does the behaviour align with people’s goals and values?

Do people have plans in action to achieve the behaviour?

Do people believe that they can do the behaviour successfully? 

Automatic motivation

Do people have the habit of doing it?

Do people feel good about doing/not doing the behaviour?

Do people feel bad about doing/not doing the behaviour?

Are people rewarded for doing/not doing the behaviour?

✅ COM-B recognises that behaviour is influenced by many factors, and it allows for a comprehensive approach to behaviour change. For example, by considering factors outside of the individual (opportunity).

✅️ COM-B is rigorous and evidence-based.

✅ COM-B offers a structured approach to identifying barriers to behaviour, and it can be presented at different levels of complexity, which makes it particularly useful to engage stakeholders from that come from different educational backgrounds.

⛔️ Although it has been praised for allowing for systematic categorisation and replication of behaviour change intervention, some authors have argued that COM-B obviates variability in behaviour by reducing it to capability, opportunity and motivation [4,5].

⛔️ COM-B is an academic model that tends to be used in the context of health behaviour, and its application to other contexts may be less straightforward.

⛔️ Although the main premise of COM-B is simple, the model can be difficult to explain once we start going deeper into the different layers of complexity.

🧠 For a journal article on COM-B and the Behaviour change Wheel read: The behaviour change wheel: A new method for characterising and designing behaviour change interventions. Read more about the Behaviour Change Techniques taxonomy here: The Behavior Change Technique Taxonomy (v1) of 93 Hierarchically Clustered Techniques: Building an International Consensus for the Reporting of Behavior Change Interventions

📢 For an introduction to COM-B from Prof Susan Michie watch: Introducing COM-B

📚 For a detailed guide on intervention design (COM-B diagnosis, link between COM-B and TDF, BCW and BCTs) get: The Behaviour Change Wheel: A guide to designing interventions