• What is the difference between the theory of reasoned action and the theory of planned behavior? [Answer / Close]

    The theory of reasoned action (TRA) is a special case of the theory of planned behavior (TPB). The only difference between the two theories is that the TPB includes behavioral control as an additional determinant of intentions and behavior. In the development of the TRA it was assumed that people have volitional control over the behavior of interest (and that they realize that they are capable of performing the behavior if they so desire). Under these conditions, behavioral control becomes irrelevant and the theory of planned behavior reduces to the theory of reasoned action.

  • Where can I find the standard TPB questionnaire? [Answer / Close]

    There is no standard TPB questionnaire. In most published research papers, you can find detailed information about the questionnaire used by the investigator. A sample questionnaire is availabe online ( Sample Questionnaire). However, the items employed in previous research and the items shown in the sample questionnaire may not be appropriate for your behavior, population, or time period. Formative research is therefore required to construct a new questionnaire suitable for the behavior and population of interest. If beliefs are to be assessed, they must be elicited anew from a representative sample of the research population. Similarly, items designed to directly assess the theory's constructs must be validated prior to construction of the final questionnaire. (See Constructing a TPB Questionnaire.)

  • I am interested in using the TPB in a certain behavioral domain. How can I find out whether anybody has applied the TPB to this domain before, and where can I find relevant publications? [Answer / Close]

    Well over 1000 empirical studies have applied the TPB in a multitude of behavioral domains. To find articles relevant to your area of interest, you can search the list of TPB references on my website, at:

    http://www.people.umass.edu/aizen/tpbrefs.html

    You can also search online databases, such as PsycINFO or Google Scholar.

  • I am studying a category of behaviors, not a single action. How can I apply the TPB to a behavioral category? [Answer / Close]

    We are often interested in predicting, explaining, or changing categories of behavior, such as exercising, studying, or conserving energy -- not any single action. It is possible to deal with such a criterion by assessing attitudes, subjective norms, perceptions of control, intentions, and actual behavior with respect to each of a representative set of actions that comprise the category of interest. These measures can then be aggregated to arrive at indices representing the behavioral category.

    However, if the investigator has no particular interest in the individual actions that comprise the category, a simpler strategy can be adopted. Participants can be given a description of the behavioral category, and all TPB measures are obtained in relation to the category as a whole. For example, the participants could be told that we are interested in vigorous exercise defined as 30 minutes or more of physical activity that produces a sweat, at least three times a week. The TPB constructs are then assessed with respect to this criterion.

  • My behavioral criterion is a choice among alternative options. How can I use the TPB in this situation? [Answer / Close]

    Strictly speaking, every behavior involves a choice, even if the choice is between performing or not performing the behavior. In some cases, beliefs about not performing a behavior may largely be mirror images of beliefs about performing it. In this case, we can simply assess the TPB constructs in relation to performing the behavior.

    However, sometimes different beliefs are readily accessible in relation to the behavioral alternatives. For example, if we are interested in travel-mode choice, the beliefs that are readily accessible with respect to using public transportation may not simply be mirror images of using one's car. If practical, therefore, it is recommended that in this case the TPB constructs be assessed in relation to both options under consideration.

  • How many participants should I include in my pilot study to elicit readily accessible behavioral, normative, and control beliefs? [Answer / Close]

    The answer depends on the nature of the research population and on the objectives of the study. As a rule of thumb, the pilot study should include a sample of 25 to 30 participants representative of the general research population. However, if you are interested in differences among subpopulations (differences based on ethnicity, gender, age, etc.), you should stratify your sample accordingly with a sample size of 25 to 30 participants for each subpopulation.

  • Is it appropriate to use focus groups to elicit accessible behavioral, normative, and control beliefs? [Answer / Close]

    The preferred method for eliciting accessible beliefs is a free-response format in which individuals are asked to take a few minutes to list, with respect to the behavior of interest, the likely outcomes, normative referents, and control factors that come readily to mind (see Constructing a TPB Questionnaire).

    In the TPB, the beliefs that come readily and spontaneously to mind are assumed to be the prevailing determinants of attitude toward the behavior, subjective norm, and perceived behavioral control. These many not be the beliefs identified when employing focus groups. By encouraging discussion of ideas brought up by individual group members, focus groups can lead to the selection of beliefs that are not readily accessible for most people.

  • Can the belief composites (Σbiei, Σnimi, Σcipi) substitute, respectively, for direct measures of attitude, subjective norm, and perceived behavioral control? [Answer / Close]

    Not necessarily. Theoretically, attitudes are based on behavioral beliefs, subjective norms on normative beliefs, and perceived behavioral control on control beliefs. However, these propositions are subject to empirical test. The validity of the belief composite measures is typically tested by correlating each composite with the direct measure of the corresponding construct.

  • Do I have to assess behavioral, normative, and control beliefs in addition to obtaining direct measures of attitude, subject norm, and perceived behavioral control? [Answer / Close]

    The answer depends on the purpose of your research. If you just want to predict intentions and behavior, the direct measures of attitude, subjective norm, and perceived behavioral control are sufficient. Among other things, these measures allow you to examine the theory's predictive validity and to estimate the relative importance of attitude, subjective norm, and perceived behavioral control. However, if you would like to understand the factors that provide the basis for these variables (perhaps to design an effective behavior change intervention) you also must elicit and assess the accessible behavioral, normative, and control beliefs.

  • For the prediction of intentions, should I use the direct measures of attitude, subjective norm, and perceived behavioral control or the aggregates of behavioral, normative, and control beliefs? [Answer / Close]

    Standard attitude scaling procedures are used to assess attitude, subjective norm, and perceived behavioral control in a relatively direct manner. According to the theory, the composite indices of behavioral, normative, and control beliefs capture, respectively, the underlying determinants of these constructs. The direct measures should therefore be used to predict intentions.

  • Can I use a measure of intention as a proxy for a measure of behavior? [Answer / Close]

    Generally speaking, we cannot use a measure of intention as a substitute for a measure of behavior. Many factors can prevent people from carrying out their intentions (see question below). It follows that a measure of intention will not necessarily predict actual behavior, and that a change in intentions will not necessarily be followed by behavior change. How closely linked they are is an empirical question. We may be able to justify using intention as a proxy for behavior if we have independent evidence for a strong intention-behavior correlation with respect to the behavior, population, context, and time period under investigation.

  • Why is my measure of intention a poor predictor of actual behavior? [Answer / Close]

    We often observe a discrepancy between expressed intentions and actual behavior. Among the factors that can contribute to the intention-behavior gap are the following.
  • Lack of compatibility: The measures of intention and behavior are incompatible in terms of their levels of specificity/generality or in terms of the measurement scales used.
  • Restriction of range: There is little variance in the measures of intention and/or behavior.
  • Forgetting: People forget to act on their intentions in a timely manner.
  • Low control: People lack adequate control over performance of the behavior, despite their favorable intentions.
  • Change of mind: New information becomes available that changes previously assessed intentions such that they are no longer predictive of behavior.
  • Hypothetical bias: The beliefs that are readily accessible in memory when intentions are assessed differ substantially from the beliefs that are readily accessible in the behavioral context.
  • Is it possible and appropriate to assess behavior at the same time as intention (and the TPB's other components)? [Answer / Close]

    It is possible to measure intention and behavior at the same time. For example, we can measure intention to exercise in the next three months and, at the same time, obtain a measure of exercise behavior during the previous three months. Of course, the correlation between these two measures only provides an indication of the extent to which current intentions are consistent with previous behavior. The correlation can be taken as an indication of the intention's predictive validity only if there is independent evidence to suggest that the behavior in question has a high degree of temporal stability. Thus, if it is know that later exercise behavior correlates strongly with prior exercise behavior in the population of interest, then the measure of past behavior can serve as a proxy for a measure of future behavior. However, this correlation may be inflated if participants misremember, misconstrue, or misrepresent their reported past behavior such that it is more consistent with current intentions than it actually was.

  • How do I estimate the reliability and validity of my direct TPB measues? [Answer / Close]

    The reliability and validity of direct TPB measures are estimated in formative research. First, a TPB questionnaire is constructed in accordance with established guidelines (See Constructing a TPB Questionnaire). The direct items (reflective indicators) designed to assess the TPB constructs (attitude, subjective norms, perceived behavioral control, intention, and behavior) are then tested for convergent and discriminant validity. Confirmatory factor analysis is the preferred method, although many investigators only report Cronbach's alpha for each construct, a measure of internal consistency.

    Note that internal consistency is not a requirement of the behavioral, normative, and control belief composites because different accessible beliefs may well be inconsistent with each other. Also, if reliability in the sense of temporal stability is also considered important, the questionnaire must be administered a second time and test-retest correlations are computed.

    Evidence for predictive and construct validity is obtained when research using the measures developed by the investigator supports the predictions derived from the theory.

  • The items I have used to assess one or another of the components in the TPB (attitudes, subjective norms, perceived behavioral control, intentions, behavior) show low internal consistency. What should I do? [Answer / Close]

    Direct TPB measures should be developed in pilot work to make sure that they have satisfactory psychometric properties. If you have multiple items for each construct, you may be able to drop one or two and thereby increase internal consistency and discriminant validity. When this is not possible, the correct procedure is to start over again, develop adequate measures, and then collect your data.

  • Is it appropriate to use multiple regression analysis to determine the relative importance of beliefs, or to select beliefs to be targeted in a behavioral intervention? [Answer / Close]

    Theoretically, all readily accessible behavioral beliefs (usually elicited in a free-response format) are important determinants of attitude, all readily accessible normative beliefs are important determinants of subjective norm, and all readily accessible control beliefs are important determinants of perceived behavioral control. Consistent with this, all beliefs are given equal weight in the expectancy-value model. If you use each participant's personal beliefs, therefore, there is no need to identify their relative importance. However, when we use modal accessible beliefs (i.e., when we select the most frequently emitted beliefs in a sample of respondents), not all beliefs are readily accessible for everybody. In this case, multiple regression, structural equation modeling, latent class analysis, or other stastical methods may be used to identify the beliefs that are most important in the research population.

  • May I use 5-point (or 9-point) "Likert" scales instead of the recommended 7- point scales to assess the theory's constructs? [Answer / Close]

    Most investigators working with the TPB use 7-point bipolar adjective scales (e.g., harmful - beneficial), often mistakenly called "Likert" scales. The format of these scales is based on work with the semantic differential which found 7 points to be optimal. However, there is nothing sacred about 7 points and it is at the investigator's discretion to use fewer or more scale points.

  • In the TPB, beliefs are summed to produce composites of behavioral, normative, and control beliefs (Σbiei, Σnimi, Σcipi). However, my belief elicitation resulted in different numbers of modal behavioral, normative, and control beliefs. To control for this, should I compute the mean rather than the sum for each set of accessible beliefs? [Answer / Close]

    In the case of modal accessible beliefs (i.e., the same set of beliefs for all respondents), it is immaterial whether the beliefs are aggregated by summation or averaging. The mean is a simple linear transformation of the sum. Such a transformation has no effect on the correlation of the aggregate measure with any other variable.

    Note that different considerations apply to personal accessible beliefs, i.e., beliefs emitted by the participants themselves. Here, it is assumed that the beliefs listed represent a person's total set of accessible beliefs. Unlike modal accessible beliefs which are the same in number for all participants, different individuals may well hold different numbers of personal behavioral beliefs, different numbers of personal normative beliefs, and different numbers of personal control beliefs. According to the theory, the greater the number of favorable beliefs, the more favorable will be the attitude, subjective norm, or perceived behavioral control. Personal accessible beliefs should therefore be summed, not averaged, because computing a mean would eliminate these theoretically meaningful differences between individuals.

  • Does it make sense to measure outcome evaluations when the outcomes are obviously positive or negative? [Answer / Close]

    Some outcomes associated with a behavior receive uniformly positive or negative evaluations. For example, one of the behavioral beliefs about eating a low-fat diet may be that this behavior "reduces the risk of cardio-vascular disease." When asked to evaluate this outcome on, e.g., a 7-point good - bad scale, virtually all participants will give it a positive evaluation, and having the negative side of the scale may be irritating or confusing. Nevertheless, some people may value the outcome more favorably than others. To capture this variance, and avoid annoying the participants, we can use a unipolar evaluative scale, such as a 7-point scale that ranges from slightly good to extremely good. Alternatively, we could ask participants to rate how important it is for them to reduce the risk of cardio-vascular disease on, e.g., a 7-point not at all important to extremely important scale. Note, however, that importance ratings can be used only when the valence of the outcome (positive or negative) is clearly established because positive as well as negative outcomes can be judged important.

  • My measures of attitude, subjective norm, and perceived behavioral control correlate significantly with each other. Shouldn't these variables be independent? [Answer / Close]

    Attitude (A), subjective norm (SN), and perceived behavioral control (PBC) are conceptually independent predictors of intentions. However, empirically they are usually found to be intercorrelated because the same information can influence behavioral, normative, and/or control beliefs, the theoretical antecedents of A, SN, and PBC, respectively. For example, the information that medical research has established the superiority of an easy to prepare low-fat diet for lowering serum cholesterol may lead to the formation of the behavioral belief that "my eating a low-fat diet will reduce my serum cholesterol level," the normative belief that "my doctor thinks I should eat a low-fat diet," and the control belief that "I have the ability to prepare a low-fat diet."

  • How can I measure the relative importance of attitude, subjective norm, and perceived behavioral control in the prediction of intention? [Answer / Close]

    The relative importance of the three predictors is not measured but, instead, is estimated by means of multiple regression or structural equation analyses. The standardized regression or path coefficients serve as estimates of the relative importance (weights) of the predictors.

  • What is the difference between perceived behavioral control and self-efficacy? [Answer / Close]

    Conceptually, there is no difference between perceived behavioral control (PBC) and self-efficacy (SE). Both refer to people's beliefs that they are capable of performing a given behavior. Operationally, however, PBC and SE are usually assessed in different ways. Research with Bandura's concept of self-efficacy usually defines a graded series of potential obstacles to performance of the behavior, and participants are asked to indicate how likely it is that they could overcome each obstacle. To assess PBC, participants are usually asked to rate the extent to which they have the ability to perform the behavior, how much the behavior is under their control, etc. (see Constructing a TPB Questionnaire). It would be a mistake to assume that some of these items (e.g., rated ability to perform the behavior) assess SE whereas other items (e.g., the extent to which the behavior is under my control) assess PBC.

  • What is the difference between perceived behavioral control and locus of control? [Answer / Close]

    Perceived behavioral control (PBC) refers to people's beliefs that they are capable of performing a given behavior. Locus of control (LC) has to do with the generalized belief that events in one's life are caused by internal factors (e.g., ability or motivation) as opposed to external factors (e.g., other people, nature, or luck). Even domain-specific LC (e.g., health locus of control) has to do with a broad range of behaviors and events, not control over performance of a particular behavior. Moreover, internal control should not be equated with high PBC, nor should external control be equated with low PBC. Perceived lack of ability is an internal causal factor, but it would produce a sense of low PBC. Similarly, performance of a behavior may depend on the cooperation of others (an external factor), but people may believe that they nevertheless have high behavioral control because they are confident of obtaining the needed cooperation.

  • I know how to measure perceived behavioral control, but how do you measure actual behavioral control? [Answer / Close]

    In the TPB, actual behavioral control (ABC) moderates the effect of intentions on behavior. An essential prerequisite for assessing a person's ABC is a good understanding of the various internal factors (skills, knowledge, physical stamina, intelligence, etc.) and external factors (legal barriers, money, equipment, cooperation by others, etc.) that are needed to perform the behavior or that can interfere with its performance; as well as a way to assess the extent to which the person has or can obtain the requisite resources and overcome potential barriers. Because it is usually much more difficult to measure actual behavioral control than perceived behavioral control (PBC), most studies rely on PBC as a proxy for ABC.

  • Why doesn't the TPB account for more variance in my measure of intention or behavior? [Answer / Close]

    Several factors may be responsible for a relatively low proportion of explained variance in observed intentions or behavior.
  • There may be little meaningful variance in the criterion if, for example, most participants in the study intend to, and/or actually engage in the behavior under investigation.
  • Events intervening between questionnaire administration and observation of behavior may have produced changes in beliefs, attitudes, and intentions. As a result, the original measures are no longer predictive of the behavior.
  • The measures of the theory's constructs, including intention and behavior, may be unreliable, containing a large proportion of error variance.
  • The predictors and criteria are incompatible, i.e., they are measured at different levels of specificity or generality.
  • The factors included in the TPB are not sufficient. Other factors, such as moral norms or strong habits, may also influence the particular intention or behavior under investigation. It may be possible to measure some of these factors and add them to the theory in order to improve prediction.
  • It is, of course, also possible that the TPB, even with the inclusion of additional factors, is unable to provide accurate prediction of the intention or behavior under investigation.
  • May I expand the TPB by adding predictors that I believe are important determinants of intention and behavior? [Answer / Close]

    The TPB is, in principle, open to the inclusion of additional predictors. However, for the sake of parsimony, additional predictors should be proposed and included in the theory with caution, and only after careful deliberation and empirical exploration. Among the criteria that should be met by any proposed addition are the following.
  • Like the theory's existing predictors (attitude toward the behavior, subjective norm, perceived behavioral control, and intention), the proposed variable should be behavior-specific, conforming to the principle of compatibility. That is, it should be possible to define and measure the proposed factor in terms of the target, action, context, and time elements that describe the behavioral criterion.
  • It should be possible to conceive of the proposed variable as a causal factor determining intention or action.
  • Proposed additions should be conceptually independent of the theory's existing predictors, rather than be redundant with them.
  • The factor considered should potentially be applicable to a wide range of behaviors studied by social scientists.
  • The TPB focuses on dispositions to perform a particular behavior, but what about such more general dispositions as personality characteristics, values, demographic variables, and so forth? Aren't we missing out on important information if we neglect these variables? [Answer / Close]

    Personality traits, intelligence, demographic variables, values, and other variables of this kind are considered "background factors" in the TPB. They are not neglected but assumed to influence intentions and behavior indirectly by affecting behavioral, normative, and/or control beliefs. That is, the components of the TPB are assumed to mediate the effects of background factors on intentions and actions. The theory acknowledges that background factors can provide valuable information about possible precursors of behavioral, normative, and control beliefs, information not provided by the theory itself. Conversely, with the aid of the TPB it becomes possible to examine why a given background factor influences, or fails to influence behavior by tracing its effects via the more proximal antecedents of the behavior.

  • I have carefully followed instructions for the construction of a TPB questionnaire, yet one of the three predictors does not make a significant contribution to the prediction of intentions. Does this finding disconfirm the theory? [Answer / Close]

    No, there is nothing in the theory to suggest that attitude, subjective norm, and perceived behavioral control will each make a significant contribution to the prediction of intention. The relative importance of these three factors is likely to vary from one behavior to another and from one population to another. In some cases, one or another of the three factors will be found to have no significant effect on intention. Assuming that the factors were measured with equal reliability, lack of predictive validity merely indicates that for this particular behavior and population, the factor in question is not an important consideration in the formation of intention.

  • Is implementation intention the same as a very specific behavioral or goal intention? [Answer / Close]

    No, investigators define their behavioral criteria at a level of specificity or generality suitable for their purposes, typically at an intermediate level (e.g., donating blood or exercising on a regular basis). The details (mostly context and time) specified in an implementation intention are usually of no interest to the investigator. When forming an implementation intention, participants are asked to indicate when, where, and how they plan to implement their (goal) intentions to increase the likelihood that the intention will be carried out, not because of any inherent interest in these details. The behavioral criterion remains the more general goal intention.

    Furthermore, even when the goal intention of interest to the investigator is relatively specific (e.g., exercising every weekday in the gym during lunch hour), implementation intentions -- although also very specific as to place, time, and modality -- can be formulated only for positive goal intentions. Thus, it makes little sense to ask where, when, and how you plan to exercise if you have not formed an intention to engage in this behavior.

  • What is the role of knowledge or information in the theory of planned behavior? [Answer / Close]

    Knowledge, or correct factual information, plays no direct role in the TPB. Although information in the form of behavior-relevant beliefs is a central component of the theory, whether that information is correct or incorrect is immaterial. What matters is whether the information works for or against performance of the behavior.

    Consider, for example, a woman's belief that breast self-examination allows her to distinguish between benign lumps and malignant tumors. Although factually wrong, this item of "knowledge" would tend to support performing BSE. Thus, we cannot expect a direct correlation between amount of correct factual information on one hand and attitudes, intentions, and behavior on the other.

  • Can the theory of planned behavior be used in qualitative research? [Answer / Close]

    The TPB was developed to predict and explain human social behavior, and to serve as a framework for behavior change interventions. Like other theories of this kind, it can be used as a heuristic framework to guide questions to be raised in qualitative research. However, the standard methods developed over the years for use with the theory are largely quantitative in nature. The only part of these methods that requires qualitative research is the elicitation and coding of readily accessible behavioral, normative, and control beliefs (See Constructing a TPB Questionnaire).

  • The propositions in the theory of planned behavior seem to be self-evident. Can the theory be falsified? [Answer / Close]

    The TPB makes specific predictions that can be tested in empirical research. Among other things it predicts a number of mediating and moderating processes: (1) Intention mediates the effects of attitude and subjective norm on behavior; (2) Perceived behavioral control moderates the effect of intention on behavior; (3) Beliefs influence intentions and behavior indirectly by their effects on attitudes, subjective norms, and perceived behavioral control; (4) Background factors (e.g., personality traits, values, demographic characterists, etc.) influence behavior only indirectly by their effects on beliefs. In addition, the TPB specifies the way in which behavioral beliefs influence attitude, normative beliefs influence subjective norm, and control beliefs influence perceived behavioral control. Methodically sound empirical research that disconfirms these predictions would tend to falsify the theory.

  • How can I get permission to use the TPB in my research, or to include a figure of the theory in my thesis, dissertation, presentation, poster, article, or book? [Answer / Close]

    The theory of planned behavior is in the public domain. No permission is needed to use the theory in research, to construct a TPB questionnaire, or to include an original drawing of the model in a thesis, dissertation, presentation, poster, article, or book. However, if you would like to reproduce a published drawing of the model, you need to get permission from the publisher who holds the copyright. You may use the drawings on this website for non-commercial purposes, including publication in a journal article, so long as you retain the copyright notice.

  • Could you look at my research plan, questionnaire, model, or project and comment on it? [Answer / Close]

    I receive many requests for assistance and it is simply impossible for me to devote time to each. If you have a budget for consultation, I will be glad to discuss the terms with you. Otherwise, I suggest you carefully examine this website. On it you will find guidance on how to apply the theory of planned behavior, a sample TPB questionnaire, copies of many of my publications, a bibliography of TPB references, as well as answers to many questions you may have. If, after perusing the site, you still have one or two quick questions, email me and I'll try to answer them.