Theory of Planned Behavior — Ajzen (1991)
The Theory of Planned Behavior (TPB) explains intentions and behavior through attitude, subjective norm and perceived behavioral control (Ajzen, 1991). Its measures are built for each study following Ajzen's guidelines, not as one fixed scale.
What it measures
TPB predicts behavioral intention and behavior from three constructs: attitude toward the behavior, subjective norm (perceived social pressure) and perceived behavioral control (PBC). Intention is the main proximal predictor of behavior.
TPB is a framework, not a single off-the-shelf scale. Items are written for the specific behavior under study, following Ajzen's recommendations. Intention, subjective norm and PBC are usually measured as reflective factors, while attitude often uses semantic-differential evaluative items — and belief-based composites (behavioral, normative and control beliefs) are formative indices, so internal-consistency statistics do not apply to them.
Scale items
The item wording is under the publisher’s copyright, so we do not reproduce it here. You can find the full items in the original article (see the citation below). In Explonia, signed-in users get this scale complete in the built-in library and can add it to their own study — no need to find the items yourself. For use in your own research; please cite the original source.
How to use and cite it
Cite Ajzen (1991), Organizational Behavior and Human Decision Processes, for the theory, and follow Ajzen's published guidance for constructing the questionnaire for your specific behavior. Because items are context-specific, you write them yourself for your behavior and population rather than copying a fixed item set.
In Explonia (Academic tier) you can build the TPB constructs, then run reliability on the reflective ones, CFA and SEM, with an exportable APA write-up. For wording help, see writing good survey questions.
Reporting reliability and validity
Apply internal-consistency statistics (alpha, omega, composite reliability ≥ .70) and AVE (≥ .50) only to the reflective constructs (typically intention, subjective norm, PBC and reflective attitude items). Do not apply Cronbach's alpha to formative belief composites — they are not expected to be internally consistent; instead assess indicator weights and collinearity. Keep at least three items per reflective factor, and report validity evidence separately from reliability.
Reference table
| Property | Detail |
|---|---|
| Construct | Attitude, subjective norm, perceived behavioral control, intention |
| Type | Mixed: reflective constructs + formative belief composites; multidimensional |
| Number of items | Context-specific — researchers build items per behavior following Ajzen's guidelines |
| Response format | Typically 7-point Likert and semantic-differential items |
| Original source | Ajzen, I. (1991). Organizational Behavior and Human Decision Processes, 50(2), 179–211. |
| DOI | 10.1016/0749-5978(91)90020-T |
| Reported reliability | Varies by study and behavior — report per construct (and not for formative composites) |
| Domain | Social psychology / behavior prediction |
Frequently asked questions
Is there a standard TPB questionnaire?
No single fixed questionnaire. TPB is a framework; you write items for the specific behavior following Ajzen's published construction guidelines. Cite Ajzen (1991) for the theory and report your exact measures.
Should I run Cronbach's alpha on TPB belief measures?
Only on the reflective constructs (such as intention, subjective norm and PBC). Belief-based composites (behavioral, normative, control beliefs) are formative, so internal-consistency coefficients do not apply — assess indicator weights and collinearity instead.
How to cite this page
If this page helped your research, you can cite it (APA 7):
Szymkowiak, A. (2026). Theory of Planned Behavior Scales (Ajzen 1991). Explonia. https://explonia.com/scales/theory-of-planned-behavior/
Last updated: July 2026
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