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Theory of planned behaviour matters because it explains a gap many clinicians see, someone can fully intend to change and still not do it. Ajzen proposed that behaviour is best predicted by intention, and that intention is shaped by attitude, subjective norm, and perceived behavioural control, three separate influences on how strongly someone intends to act. For example, imagine a patient who wants to lose weight, whose family supports the plan, and who feels confident she can follow it: despite this strong intention, life events can still stop her acting on it. In practice, this intention-behaviour gap means clinicians should also address practical barriers to action, not just build motivation.

Attitude is the person's own positive or negative evaluation of the behaviour. Subjective norm is their perception of whether people who matter to them approve of the behaviour. Perceived behavioural control is how easy or difficult they believe the behaviour will be, reflecting confidence and access to resources. These three combine to form intention, which is the closest predictor of actual behaviour, though the theory itself calls this last step the intention-behaviour gap, since intention does not always convert into action. Take a doctor who intends to exercise daily, has a positive attitude, supportive colleagues, and feels able to do it, yet still skips most sessions once a busy on-call week begins. In practice, interventions that only target attitude and norms, e.g. education campaigns, often fail to close the intention-behaviour gap unless they also address perceived behavioural control, such as removing practical obstacles.

• In the theory of planned behaviour, one component is proposed to influence behaviour both through intention and directly. Which component has that dual pathway?
• The theory holds that each of its three components is itself built from underlying beliefs. Which belief type underlies the subjective norm component?
• A researcher wants to close the gap between a patient's strong intention to exercise and her actual behaviour. Which technique has the best evidence for bridging that gap?
• A critic argues the model predicts what people mean to do far better than what they actually end up doing. What does the evidence broadly show about this criticism?

• Health belief model, predicts action directly from susceptibility, severity, benefits, and barriers, unlike the theory of planned behaviour's intention step.
• Self-efficacy, overlaps with perceived behavioural control but is Bandura's broader, task-specific confidence construct, rather than one component of this specific model.
• Intention-behaviour gap, the theory's own named limitation for why intention sometimes fails to become action, unlike models that assume intention converts directly into behaviour.
• Locus of control, a general trait about who controls outcomes, unlike this theory's behaviour-specific attitude, norm, and control judgements.

• That is the mediating variable rather than a component with dual paths.
• That is not one of the model's three named components.
• That component acts on behaviour only through intention.
• Those beliefs form part of the attitude component.
• Restating a general intention does not create a concrete cue to act.

• Name the learning, social or research principle being tested before reading the options.
• Identify the antecedent, behaviour, consequence or cognitive process in the vignette.
• Compare the direction of effect with the nearest competing principle.
• Apply the same rule to a new example to confirm that the answer transfers.