Theory of Planned Behavior (TPB) - Ajzen (1991)

Theory Publication Information

Citation Information

Why Was the Model Created?

Icek Ajzen developed the Theory of Planned Behavior to address critical limitations in the Theory of Reasoned Action and provide a more comprehensive framework for understanding behavior across diverse domains. The fundamental motivation stemmed from recognizing that TRA, while successful in predicting behavior under conditions of volitional control, failed adequately when individuals lacked complete control over behavior performance.

While TRA successfully predicted voting, family planning, and consumer choice, it operated under an assumption that behavior results solely from conscious intentions determined by attitudes and subjective norms. This assumption proved problematic in real-world contexts where individuals often cannot fully control behavior performance due to resource constraints, skills limitations, environmental obstacles, or structural barriers. Many significant behaviors, including technology adoption, involve elements beyond complete volitional control.

Ajzen explicitly constructed TPB to overcome this limitation by adding perceived behavioral control - the extent to which individuals believe they can successfully perform behavior even when facing obstacles. By incorporating control perceptions, the TPB creates applicability to behaviors where volitional control varies. Beyond technology adoption, the framework aims to explain intentional behavior across health, education, environment, relationships, and organizational contexts with consistent theoretical structure while allowing domain-specific applications.

Core Concepts and Definitions

TPB operationalizes five core constructs, including the three primary determinants of behavioral intention:

• Attitudes Toward Behavior: Overall favorable or unfavorable evaluations of performing a specific behavior. Reflect underlying beliefs about behavior consequences weighted by desirability of those consequences.
• Subjective Norms: Perceived social pressure to perform or not perform behavior. Capture perceptions of what important others think the individual should do, weighted by motivation to comply with each referent.
• Perceived Behavioral Control:People’s perception of the ease or difficulty of performing the behavior of interest. Unlike generalized locus of control, PBC is behavior-specific and varies across situations. Reflects both internal factors (skills, knowledge) and external factors (opportunities, resources, cooperation of others).
• Behavioral Intention: Readiness or plan to perform behavior. Represents the immediate antecedent to actual behavior performance.
• Behavior: The observable action performed, whether individuals actually perform intended behaviors.

What Does the Model Measure?

The Theory of Planned Behavior is a measurement model. Ajzen (1991) and Ajzen’s subsequent TPB measurement guidance specify how each construct is operationalized:

• Attitude Toward the Behavior (AB): Overall favorable/unfavorable evaluation of performing the behavior; typically measured via semantic-differential items (good-bad, pleasant-unpleasant, beneficial-harmful, wise-foolish).
• Subjective Norm (SN):Perceived social pressure from important referents; measured via direct perception items and underlying normative-belief × motivation-to-comply products.
• Perceived Behavioral Control (PBC):Perceived ease/difficulty of performing the behavior, including both self-efficacy and controllability facets. Measured via direct items (e.g., “For me to perform X is easy/hard”) and underlying control-belief × power-of-factor products.
• Behavioral Intention (BI): Self-reported plan or willingness to perform the behavior.
• Behavior (B): Observed action, ideally matched to intent on action, target, context, and time (principle of compatibility inherited from TRA).
• Underlying Beliefs:Behavioral beliefs (bi) × outcome evaluations (ei), normative beliefs (nj) × motivation to comply (mj), and control beliefs (ck) × power factors (pk) - typically elicited through open-ended belief elicitation before scale construction.

Ajzen (1991) and the accompanying construction guidance (Ajzen, 2006) describe belief elicitation, pilot testing, and scale construction procedures. TPB has an extensive validation record across health, consumer, and technology adoption behaviors; meta-analyses commonly report that TPB variables explain a substantial portion of variance in intention and a smaller but meaningful portion of variance in behavior.

Preceding Models or Theories

TPB built logically upon several prior theoretical traditions:

• Theory of Reasoned Action (Fishbein & Ajzen, 1975): Provided the foundational structure where intentions mediate the attitude-behavior relationship.
• Self-efficacy theory (Bandura, 1977): Developed the self-efficacy construct - beliefs about personal capability to perform actions - which TPB draws on via perceived behavioral control.
• Locus of control research:Documented how individuals’ beliefs about control over outcomes influence behavior.
• Expectancy-value theories: Grounded the concept that attitudes form from expected consequences weighted by their evaluations.
• Behavioral decision theory: Provided foundations for understanding how people make deliberate behavior choices.

Describe the Model

The Theory of Planned Behavior specifies that attitudes, subjective norms, and perceived behavioral control determine behavioral intention, which in turn predicts actual behavior. Perceived behavioral control additionally exerts direct effects on behavior when control accurately reflects actual constraints. This hierarchical structure is:

Attitudes & Subjective Norms & Perceived Control → Behavioral Intention → Behavior

What does the model measure?

• Attitudes toward behavior: Evaluative scales capturing favorable/unfavorable judgments of performing specific behaviors.
• Subjective norms: Perceived social pressure and normative expectations from important referent others.
• Perceived behavioral control: Beliefs about factors facilitating or impeding behavior performance and power of each factor.
• Behavioral intention: Readiness and plans to perform behavior measured through likelihood and expectancy items.
• Actual behavior: Whether individuals actually perform intended behaviors, measured through self-report or behavioral observation.

Main Strengths

• Theoretical comprehensiveness: Incorporates personal evaluation, social influence, and self-efficacy into single coherent framework.
• Clear causal structure: Articulates explicitly specified relationships enabling precise hypothesis testing and systematic investigation.
• Measured flexibility: Can be applied to any specific behavior by conducting formative research identifying relevant beliefs and control factors.
• Cross-domain validation: Demonstrates predictive validity across health, education, environment, workplace, and consumer domains.
• Distinction of indirect and direct effects: Specifies that perceived control affects behavior both through intentions and directly, reflecting control factor complexity.
• Practical intervention guidance: Explicitly specifies attitudes, norms, and control as change targets, directing practitioners toward psychosocial factors requiring modification.

Main Weaknesses

• Measurement circularity concerns: Perceived and actual behavioral control may coincide or diverge due to biased perceptions, creating ambiguity about what perceived control predicts.
• Limited attention to structural barriers: Treats barriers primarily through individual perceptions; real structural barriers preventing adoption receive less theoretical attention.
• Temporal dynamics underspecified: Provides limited specification of how intentions change over time or how to maintain intentions across extended implementation periods.
• Past behavior undertheorized: Focuses on rational deliberation processes but provides limited mechanism for habit formation and automaticity in repeated behavior.
• Affective factors underemphasized: Attitude construct focuses on instrumental evaluations rather than emotional or affective responses to behavior.
• Domain-specific inconsistency: Relative importance of attitudes, norms, and control varies substantially across domains, limiting ability to predict which factors dominate without empirical investigation.

Key Contributions

• Control factor integration: Incorporated perceived behavioral control as explicit construct affecting both intentions and behavior directly.
• Theoretical extension accomplishment: Expanded Theory of Reasoned Action applicability to behaviors beyond volitional control.
• Multi-factor integration framework: Provided model integrating attitudes, norms, and self-efficacy into unified behavioral prediction framework.
• Belief system emphasis: Moved beyond monolithic constructs toward understanding them as built from specific belief systems.
• General behavior prediction template: Provides a general framework that has been applied across health, education, environment, workplace, and consumer domains.
• Practical intervention specification: Explicitly specified psychological factors requiring modification to influence behavior, enabling targeted intervention design.

Internal Validity

Ajzen established TPB’s internal validity through multiple strategies:

• Theoretical coherence: Articulates clear causal structure with explicitly specified relationships between constructs.
• Construct operationalization: Provides explicit measurement guidance for attitudes, norms, and control through multi-item scales with clear theoretical basis.
• Empirical grounding: Builds on extensive self-efficacy, locus of control, and behavioral research, importing validity support from established literature.
• Logical extension of established theory: Maintains TRA core structure while adding perceived behavioral control, demonstrating that TPB incorporates TRA as special case.
• Specification precision: Precisely specifies which constructs exert indirect effects through intentions and which exert direct effects on behavior.

External Validity

The Theory of Planned Behavior established substantial external validity through diverse applications:

• Cross-domain applicability: Applied across health, occupational, educational, environmental, and consumer behaviors, with reported effect sizes varying by domain.
• Population diversity: Found consistent relationships across demographic groups, educational levels, and cultural contexts.
• Behavioral complexity variation: Applied to simple discrete behaviors through complex sustained behaviors requiring multiple action sequences.
• Time frame generalization: Maintained predictive validity across immediate behavior through months and years of follow-up.
• Laboratory and field study convergence: Found consistent relationships in both controlled settings and real-world behavioral contexts.

Relevance to Technology Adoption

TPB is directly relevant to technology adoption because it explains how attitudes, social influences, and perceived capability determine whether individuals intend to adopt technologies. Unlike simpler models, TPB acknowledges that individuals may intend to adopt but face actual barriers preventing adoption.

Barriers to Technology Adoption Identified by TPB

• Unfavorable attitudes: Negative evaluations of adoption consequences including job security threats, autonomy loss, or insufficient benefits relative to effort.
• Negative subjective norms: Lack of adoption pressure or active resistance from supervisors, peers, or organizational leaders.
• Low perceived behavioral control: Beliefs that learning technology requires skills one lacks, that insufficient resources exist, or that organizational impediments prevent adoption.
• Technology anxiety and confidence deficits: Fears of technology malfunction, data loss, or personal inadequacy reducing perceived control despite capability.
• Interaction barriers: Strong negative attitudes combined with normative pressure against adoption, or control barriers occurring alongside negative attitudes.

Leadership Actions TPB Prescribes

• Attitude change targeting specific beliefs: Conduct formative research identifying beliefs creating negative attitudes, then design targeted interventions addressing specific concerns.
• Normative influence interventions: Secure explicit advocacy from organizational influencers, involve respected peers in implementation planning, address cultural conflicts explicitly.
• Perceived control enhancement: Provide comprehensive training ensuring capability development, create support systems, remove actual environmental obstacles.
• Multi-factor intervention design: Address all three barrier types simultaneously rather than focusing on single-factor solutions.
• Monitoring and adaptive management: Measure attitudes, norms, and control periodically to assess whether interventions effectively address barriers and enable course correction.

Following Models or Theories

TPB provided the structural foundation for numerous extensions and integrated models:

• Technology Acceptance Model extensions: Applied TPB structures to technology-specific adoption contexts.
• Unified Theory of Acceptance and Use of Technology (UTAUT): Integrated TPB with other adoption models into comprehensive framework.
• Task-Technology Fit models: Built on TPB by incorporating how technology characteristics align with job requirements.
• Protection Motivation Theory applications: Extended TPB structures to threat-and-coping contexts.
• Health behavior adoption models: Applied TPB to diverse health behaviors and organizational health promotion.

References

1. Ajzen, I. (1991). The theory of planned behavior. Organizational Behavior and Human Decision Processes, 50(2), 179-211. https://doi.org/10.1016/0749-5978(91)90020-T
2. Bandura, A. (1977). Self-efficacy: Toward a unifying theory of behavioral change.Psychological Review, 84(2), 191-215.Back to citation 1

Further Reading

1. Ajzen, I., & Fishbein, M. (1980). Understanding attitudes and predicting social behavior. Prentice-Hall.
2. Fishbein, M., & Ajzen, I. (1975). Belief, attitude, intention, and behavior: An introduction to theory and research. Addison-Wesley.
3. Triandis, H. C. (1977). Interpersonal behavior. Brooks/Cole.
4. Armitage, C. J., & Conner, M. (2001). Efficacy of the theory of planned behaviour: A meta-analytic review. British Journal of Social Psychology, 40(4), 471-499.

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