Theory of Planned Behavior (TPB)

Theory of Planned Behavior (TPB)

Purpose

Apply Ajzen's Theory of Planned Behavior to diagnose the intention-action gap. TPB explains why people fail to do what they intend — by decomposing intention into three predictors (Attitudes · Subjective Norms · Perceived Behavioral Control) and intention into behavior (gated by actual control). When products show high stated interest but low conversion, the gap is usually one of TPB's components.

Frameworks & Standards

The Model

ATTITUDE TOWARD BEHAVIOR  ──┐
                            │
SUBJECTIVE NORMS           ──┼──→ INTENTION ──→ BEHAVIOR
                            │                    ↑
PERCEIVED BEHAVIORAL CTRL  ──┘                    │
                            │_____________________│
                                  (also directly affects behavior)

Attitude toward the behavior = personal evaluation (positive/negative feeling about performing it) Subjective Norms = perceived social pressure (what important others think you should do) Perceived Behavioral Control = perceived ease/difficulty (can I actually do this?) Intention = motivational readiness to perform the behavior Actual Behavior = the outcome (also gated by ACTUAL control, not just perceived)

Prompt Template

You are applying the Theory of Planned Behavior (TPB).

CONTEXT:
- Target behavior: [[behavior]]
- Population: [[description]]
- Current intervention or design: [[approach]]

THREE-COMPONENT DIAGNOSIS:
1. ATTITUDE diagnosis
   - Beliefs about outcomes (cognitive)
   - Affect toward outcomes (emotional)
   - Net attitude: positive / neutral / negative
2. SUBJECTIVE NORMS diagnosis
   - Important referents (who matters to this population?)
   - Perceived expectations from those referents
   - Motivation to comply with referents
3. PERCEIVED BEHAVIORAL CONTROL diagnosis
   - Self-efficacy beliefs
   - Perceived barriers
   - Perceived resources / facilitators

INTENTION-ACTION GAP DIAGNOSIS:
- Stated intention strength: high / medium / low
- Behavior conversion rate: %
- Gap source: weak intention | strong intention but low control | strong intention but social-norm violation

INTERVENTION DESIGN:
- For attitude gaps: salient-outcome highlighting
- For subjective-norm gaps: social-proof + referent-specific testimonials
- For perceived-control gaps: scaffolding + skill-building + barrier removal
- For intention-behavior gaps: implementation intentions ("when X happens, I'll do Y")

Core Principles

• Intention is a function of three things, not one. Persuading on attitude alone fails when subjective norms or control are negative.
• Subjective norms matter most in collectivist cultures and high-stakes decisions. In individualist contexts they're often weak; in family/health/career decisions they dominate.
• Perceived control predicts behavior even when intention is weak. Operators with high self-efficacy take action; operators with low self-efficacy delay even when motivated.
• Implementation intentions close the intention-action gap. "When X situation occurs, I'll do Y action" turns intention into automatic response.
• Actual control limits perceived control's predictive power. If barriers are real (cost · time · access), perceived control matters less than reducing the real barriers.

Applications & Use Cases

Reference Materials

• Ajzen, I. (1991). "The theory of planned behavior." Organizational Behavior and Human Decision Processes 50(2): 179–211.
• Ajzen, I. (2002). "Perceived Behavioral Control, Self-Efficacy, Locus of Control, and the Theory of Planned Behavior." Journal of Applied Social Psychology 32(4): 665–683.
• Constructing Theory of Planned Behavior questionnaires — https://people.umass.edu/aizen/tpb.measurement.pdf
• Ajzen's TPB resource page — https://people.umass.edu/aizen/tpb.html

Usage Guidelines

• Measure each TPB component separately in user research. A combined "would you do X?" question hides which component is the bottleneck.
• Implementation intentions are the lowest-cost, highest-leverage intervention to close intention-behavior gaps.
• Pair with TTM (stage-of-change determines which TPB component dominates).

Collaboration Protocol

• Inbound from: behavioral-designer · conversion-optimizer · decision-architect
• Outbound to: same agents + habit-formation-coach (where the target is repeated behavior)
• Cross-framework: pairs with Transtheoretical Model (stage informs which TPB component dominates), Fogg Behavior Model (Ability ≈ Perceived Behavioral Control), Cialdini (social proof informs Subjective Norms)

Ethical Guidelines

• Manufactured subjective norms (fake testimonials · invented "everyone is doing it" claims) are dark patterns
• Inflating perceived control beyond actual control sets users up for failure
• Targeting behavior change against the user's underlying values (manipulating attitude) is unethical

Success Metrics

• TPB-component-segmented conversion rates (which component is the bottleneck?)
• Intention-behavior gap closure rate after implementation-intentions intervention
• Behavior maintenance at 90 days (TPB predicts maintenance better than initial conversion)

Related Skills

• composable-skills/frameworks/transtheoretical-model/SKILL.md — stage determines TPB component dominance
• composable-skills/frameworks/fogg-behavior-model/SKILL.md — Ability ≈ Perceived Behavioral Control
• composable-skills/frameworks/cialdinis-6-principles/SKILL.md — Social Proof = Subjective Norms
• composable-skills/frameworks/self-determination-theory/SKILL.md — Autonomous motivation strengthens all three TPB components

Testing Strategy

• Pre/post TPB questionnaires segmented by intervention type
• A/B test attitude-focused vs control-focused vs norms-focused messaging on the same population
• Expected: 20–40% lift when intervention matches the diagnosed bottleneck vs random framing

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