Theory of Planned Behavior (TPB)

Overview

The Theory of Planned Behavior (Ajzen, 1991) extends the Theory of Reasoned Action by adding perceived behavioral control as a predictor of both intention and behavior. Behavioral intention is determined by three factors: attitude toward the behavior, subjective norms, and perceived behavioral control. Intention is the proximal predictor of behavior, moderated by actual control.

When to Use

• Predicting whether a target population will adopt a new behavior (health, technology, policy)
• Diagnosing the intention-behavior gap — why people intend to act but do not follow through
• Designing persuasion or behavior change interventions by targeting the weakest predictor
• Evaluating campaign effectiveness on attitude, norm, and control dimensions

When NOT to Use

• For habitual or automatic behaviors where intention plays a minimal role
• When behavior is primarily driven by unconscious or emotional processes (use dual-process models)
• For behaviors under complete external control (no volitional component)