Why are there different versions of the COM-B model diagram?

The Capability, Opportunity, Motivation-Behaviour (COM-B) model is used to understand and predict human behaviour, and develop interventions aimed at influencing behaviour. It has been presented in several different diagrams, varying in the specification of the causal links between capability, opportunity, motivation and behaviour. The differences arise from the different levels of elaboration of the model. For many purposes the simplest version as set out in the original paper describing the model is sufficient. This version represents causal influences from capability and opportunity to motivation and bidirectional influences between these and behaviour. However, in principle there can also be causal influences from motivation to capability and opportunity, and for greater precision the diagram can show capability and opportunity influencing the relationship between motivation and behaviour rather than behaviour directly. There may be occasions when it is useful to include one or more of these additional causal specifications in the COM-B model diagram.