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Short answer
The Theory of Planned Behavior (TPB) is a cognitive psychological model developed by Icek Ajzen that predicts human behavior through behavioral intentions. Intention is determined by three core constructs: attitude toward the behavior, subjective norms, and perceived behavioral control. Researchers operationalize TPB using formative elicitation and validated multi-item questionnaires across clinical, organizational, and health studies.
Definition and scope
The Theory of Planned Behavior was formulated by social psychologist Icek Ajzen in 1985 and formally published in his 1991 paper in Organizational Behavior and Human Decision Processes. The framework extends the Theory of Reasoned Action (TRA; Fishbein and Ajzen, 1975) by adding perceived behavioral control to account for factors outside complete volitional control.
TPB applies to deliberate, reasoned actions across healthcare delivery, public health interventions, and clinical research. It models how personal evaluations, perceived social expectations, and capability appraisals converge into an intention. It does not model involuntary reflexes or unreflective habits where conscious cognitive appraisal is absent.
How it works or how it is used in practice
Under the formalization by Ajzen (1991), human action is guided by three belief structures that produce corresponding direct constructs and drive behavioral intention.
Core constructs
- Attitude Toward the Behavior: The overall favorable or unfavorable appraisal of performing the action. Indirectly, attitude represents an expectancy-value summation (∑ b_i × e_i), where behavioral beliefs (b_i) are weighted by outcome evaluations (e_i).
- Subjective Norm: The perceived social pressure from important referents. Indirectly, it reflects normative beliefs (n_i) multiplied by the motivation to comply (m_i) with those referents (∑ n_i × m_i).
- Perceived Behavioral Control (PBC): The perceived ease or difficulty of enacting the behavior. Indirectly, it reflects control beliefs (c_i) multiplied by the perceived power (p_i) of each factor to facilitate or impede action (∑ c_i × p_i).
- Behavioral Intention: The immediate cognitive precursor to behavior, capturing the conscious effort an individual plans to exert.
The TACT principle in study design
In his 2002 measurement protocol, Ajzen established that operationalizing TPB requires defining behavior using the TACT principle with identical specificity across all survey items:
- Target: The specific entity or object involved (for example, clinical practice guidelines for sepsis screening).
- Action: The explicit behavior performed (for example, completing the digital screening checklist).
- Context: The setting where the action occurs (for example, during emergency department triage).
- Time: The observation window or frequency (for example, for every newly admitted adult patient over 30 days).
Questionnaire construction protocol
Developing a TPB instrument requires a four-stage empirical process rather than ad-hoc question writing:
- Formative Elicitation Pilot: Conduct open-ended interviews with 25 to 40 individuals from the target group to identify modal salient behavioral beliefs, normative referents, and control factors.
- Salient Belief Selection: Code responses by frequency; beliefs cited by 10% to 20% of participants form the modal belief set.
- Scale Construction: Measure direct constructs with 7-point bipolar Likert or semantic differential scales. Indirect belief items use 7-point scales scored via expectancy-value products.
- Validation: Assess scale internal consistency and construct validity. Combining qualitative elicitation with structured surveys bridges qualitative research vs quantitative research approaches.
Types or related concepts
Behavioral research leverages several interconnected social-cognitive frameworks. The table below outlines how TPB compares to sibling models.
| Theory or Model | Primary Focus | Key Distinguishing Feature | Canonical Source |
|---|---|---|---|
| Theory of Reasoned Action (TRA) | Purely volitional behaviors | Models attitude and subjective norm; assumes complete volitional control without measuring control barriers | Fishbein and Ajzen (1975) |
| Theory of Planned Behavior (TPB) | Actions with non-volitional barriers | Adds perceived behavioral control (PBC) as a predictor of intention and direct proxy for actual control | Ajzen (1991) |
| Health Belief Model (HBM) | Preventive health and disease risk | Focuses on perceived susceptibility, disease severity, benefits, barriers, and cues to action | Rosenstock (1974) |
| Social Cognitive Theory (SCT) | Triadic reciprocal determinism | Centers on self-efficacy, outcome expectations, and observational learning from the environment | Bandura (1986) |
| Transtheoretical Model (TTM) | Stages of behavior adoption | Structures change across temporal stages from precontemplation to long-term maintenance | Prochaska and DiClemente (1983) |
Where it matters for labs, clinics or supply decisions
As documented in the National Cancer Institute (NCI) monograph Theory at a Glance: A Guide for Health Promotion Practice, TPB is widely applied in implementation science, hospital administration, and health services research.
Clinical protocol adherence
Hospital quality teams apply TPB to diagnose behavioral barriers behind inconsistent clinical guideline adherence:
- Infection Control: Studies assessing hand hygiene or personal protective equipment evaluate whether lapses stem from negative attitudes, peer norms, or control barriers like empty dispensers.
- Antibiotic Stewardship: In outpatient clinics, prescribing decisions are often influenced by clinician perceptions of patient expectations. TPB interventions target both normative pressures and diagnostic decision support.
- Trial Design: In clinical trials testing workflow interventions, investigators treat TPB constructs as independent vs dependent variables to determine whether training successfully altered targeted attitudes or control perceptions.
Research administration and governance
Fielding TPB surveys among clinical staff requires human subjects compliance. Investigators submit measurement protocols to an IRB in psychology or institutional review board to ensure voluntary consent and survey confidentiality. During development, running an exploratory pilot study confirms instrument reliability before broad deployment.
Common misunderstandings
Investigators frequently encounter several methodological pitfalls when applying TPB:
- Conflating PBC with Locus of Control: Locus of control is a generalized personality trait regarding overall agency. Perceived behavioral control is strictly situation-specific and behavior-specific for one defined action.
- Assuming Intention Guarantees Behavior: The intention-behavior relationship weakens when time lags are long, unforeseen obstacles arise, or actual environmental control differs from perceived control.
- Omitting Formative Elicitation: Drafting questionnaire items from intuition without pilot elicitation often fails to capture the true salient beliefs held by the target population.
- Focusing Only on Injunctive Norms: Assessing solely what others approve of misses what peers actually do in daily practice (descriptive norms), which frequently exerts stronger influence.
Frequently asked questions
Can you provide a PDF version of Ajzen’s 1991 theory of planned behavior?
The 1991 article “The Theory of Planned Behavior” was published in Organizational Behavior and Human Decision Processes (Vol. 50, Iss. 2, pp. 179–211, DOI: 10.1016/0749-5978(91)90020-T). While the formal article is held behind publisher access on ScienceDirect, Professor Icek Ajzen maintains open-access measurement guidelines, survey construction documents, and working papers on his University of Massachusetts Amherst faculty portal at people.umass.edu/aizen.
What are the three types of behavioral theories?
In public health frameworks, including the National Cancer Institute’s classification, behavioral theories are divided into three ecological levels: individual (intrapersonal) theories focusing on cognitive beliefs and attitudes (such as TPB and the Health Belief Model); interpersonal theories examining social networks and observational modeling (such as Social Cognitive Theory); and community-level theories focusing on organizational structures, policies, and systems (such as Diffusion of Innovations).
What is the difference between tra and TPB?
The primary difference between the Theory of Reasoned Action (TRA) and the Theory of Planned Behavior (TPB) is the construct of Perceived Behavioral Control (PBC). TRA assumes behaviors are under complete volitional control, using only attitudes and subjective norms to predict intention. Ajzen introduced PBC in TPB to account for skills, resources, and environmental obstacles that affect whether an intention can be enacted.
Who is the author of Planned Behavior theory?
The Theory of Planned Behavior was authored by Icek Ajzen, Professor Emeritus of Psychology at the University of Massachusetts Amherst. Ajzen co-developed the Theory of Reasoned Action with Martin Fishbein in 1975, proposed the addition of perceived control in 1985, and published the canonical formalization of TPB in 1991.
Sources
- 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. Checked 2026-11-07.
- Ajzen, I. (2002/2006). Constructing a Theory of Planned Behavior Questionnaire. University of Massachusetts Amherst. https://people.umass.edu/aizen/pdf/tpb.measurement.pdf. Checked 2026-11-07.
- National Cancer Institute (NCI). Theory at a Glance: A Guide for Health Promotion Practice (2nd ed., NIH Publication No. 05-3896). U.S. Department of Health and Human Services, National Institutes of Health. https://cancercontrol.cancer.gov/sites/default/files/2020-06/theory_at_a_glance.pdf. Checked 2026-11-07.
- Fishbein, M., and Ajzen, I. (1975). Belief, Attitude, Intention, and Behavior: An Introduction to Theory and Research. Addison-Wesley. Checked 2026-11-07.
