You may recall my blog post from last year on the Theory of Planned Behavior (TPB), titled "in praise of a failed model." My evaluation of this model was that it accurately describes the Narrative Mind, which does control intentions. But the ultimate goal of the TPB is to predict behavior, and the relationship between intentions and behavior is weak at best -- in fact, it is entirely attributable to the fact that when someone says they don't intend to do something, they probably won't do it. When they say they do intend to do it, their actual results are no better than chance, a result of the intention-behavior gap as described in Two Minds Theory.
The full TPB is shown in this diagram:
Cognitive constructs like attitudes, subjective norms, and perceived behavioral control (i.e., self-efficacy) are Narrative-system phenomena, and they do indeed have relationships with each other and with intentions (which are also products of the Narrative Mind). Perceived behavioral control has also demonstrated a weak, secondary effect as a direct predictor of behavior. That's probably because self-efficacy is related to past success or failure in performing similar behaviors, as noted in my post about Bandura's theory. In my view this is a predictive relationship and not a causal one.
As I described in my previous post, the TPB is a flexible model that has been improved over time, so it's perhaps not surprising that researchers have continued trying to improve it. In a 2008 paper, a research team from Iowa State University led by Dr. Meg Gerrard decided to add a construct called "prototypes" to the model. A prototype is defined as "the type of person who engages in specific behaviors" (p. 37). Gerrard's initial work was with risky behaviors in adolescents, so she was interested in how adolescents perceived the typical peer who engages in a risky behavior like substance use. Gerrard's version of the model described this perception as a "risk image," a characterization of the typical adolescent substance user in terms of features like intelligence, likability, selfishness, popularity, etc. The idea is that adolescents who engage in the risky behavior will then come to describe themselves that way also. Gerrard's work builds on earlier studies of prototype matching, the idea that smoking or drinking is more likely when a person's image of a smoker or drinker matches their own desired self-image (e.g., smoking cigarettes to be more like the Marlboro Man).
A prototype is a sort of archetype, with emotional features connected to social desirability and a person's self-image, which makes it different from the original TPB construct subjective norm. A subjective norm is a statistical judgment about what you think most people would do. A prototype is a mental image about what you think the person who does engage in a specific behavior is like, even if engaging in the behavior is unusual. In some cases, maybe being a rebel or iconoclast is even part of the appeal of the person who engages in the behavior.
Prototypes are posited to affect willingness to engage in a behavior, which is a more emotional type of readiness or openness that is distinct from the cognitively-focused construct of intentions. Gerrard defines willingness as "an acknowledgement that under certain circumstances, one might engage in a risk behavior that was not previously intended or sought" or as "an openness to engage in a behavior, or curiosity about a behavior that is internal rather than a reaction to social pressure" (2008 article, both definitions on p. 40). In some ways, then, willingness represents a prediction about future behavior independent of one's intentions, which is exactly the type of construct that has been found to outperform intentions in critiques of the TPB. Willingness is then predicted to have an independent effect on behavior that adds to the effect of intentions, as seen in Gerrard's 2008 modification of the TPB, which she called the Prototype Willingness Model (PWM):
Later research determined that the prototype construct had two distinct subcomponents, referred to as prototype similarity and prototype favorability. Similarity can be described as the extent to which a person sees the prototypical person engaging in the target behavior as similar to themself -- e.g., whether a person who drinks is similar to them in terms of interests, background, or personality characteristics. The favorability dimension rates whether the person likes or dislikes that prototypical example -- e.g., perhaps they think "I wish I could be more like that myself," or else "that is not the kind of person I would like to be." A simple thought experiment shows that these dimensions are orthogonal to one another: E.g., someone could easily say "yes, I'm like that, but those are the worst aspects of myself and I wish I wasn't." Or they might say "yes, I'm like that, and I love being that way!" or "no, that's not me, but I wish it was." A 2014 study found that adolescents had multiple prototypes to describe people who use alcohol excessively -- e.g., the "funny tipsy person" versus the abusive alcoholic -- and that these clusters could be readily distinguished on the basis of both favorability and similarity. Finally, the authors demonstrated that prototype similarity was a stronger predictor of adolescents' willingness to drink than prototype favorability, although both had independent effects. The figure at the top of this page, then, shows the most recent iteration of the PWM, with two different types of judgments about the prototypical person engaged in a behavior predicting the judgment-maker's willingness to engage in that behavior (i.e., their evaluation of whether they probably will do it or not). The willingness mechanism is separate from the intention mechanism as an influence on behavior, with intentions being the result of the three typical TPB factors shown at the top left of the figure.
Gerrard et al.'s 2008 article describing the PWM made reference explicitly to the Narrative/Intuitive Mind distinction that underlies Two Minds Theory (TMT). This version of the model begins with an explanation of Kahneman's System 1 (TMT's Intuitive Mind) and System 2 (TMT's Narrative Mind), and explicitly describes the Prototype Willingness Model as a "dual process" model. The original idea of the PWM, then, was essentially to graft an Intuitive-system mechanism onto the Narrative-system constructs of the existing TPB. Gerrard et al. wrote that "the reasoned, intentional process and the image-based, social reaction process can, and often do, operate simultaneously" (p. 36), and that the TPB could be improved "by combining elements of existing [Narrative-Mind-oriented] health behavior theories with heuristic [Intuitive-Mind-oriented] approaches to decision making" (p. 35). My version of the PWM at the top of the page shows the separation between the Narrative/TPB and Intuitive components of the PWM with a dotted line: The Narrative mechanisms are on top, and the Intuitive ones on the bottom.
Because of my view that the Intuitive Mind controls behavior, I would predict that the PWB's lower-level system of constructs focused on prototypes and willingness would actually outperform the upper-level system that operates at the level of the Narrative Mind. This is exactly what a 2016 meta-analysis found to be the case: At least for adult patients, the willingness pathway is more useful than the intention pathway in predicting behavior. A caveat is that the studies in this meta-analysis (like most studies of the TPB) used retrospective questionnaires, which I think means that even the data about Intuitive-Mind mechanisms are being filtered through a Narrative-Mind interpretation -- see my blog post about those measurement issues. I suspect that the advantage of PWM constructs over TPB constructs would be even more dramatic in studies that used ecological-momentary-assessment surveys instead of retrospective questionnaires. One quirk in the 2016 meta-analysis (although not in three more recent studies described below) was that the willingness pathway had a slightly lower effect size than the intention pathway in a subgroup of studies about adolescents, and the two pathways also seem to be more strongly related to one another in adolescents than they are in adults. I wonder if that’s because adolescents’ Narrative Minds (e.g., the prefrontal cortex) are less well developed, and therefore less clearly differentiated from the Intuitive-Mind variables that control their behavior.
A 2023 article on adolescents' bicycle safety found that prototype similarity and perceived behavioral control each predicted willingness, and that all three of the TPB predictors had effects on intention, but that willingness (r = .32) outperformed intention (r = .19) as a predictor of actual safety behavior. A 2021 article found that the PWM added to the explanatory power of the TPB for predicting COVID-19 prevention behaviors, although in this study the willingness construct was not measured, so the effect of prototypes showed only a weak effect on behavior that was largely by way of intentions. A 2020 articles found strong effects of both intentions (r = .53) and willingness (r = .54) on behavior, with prototypes operating via both mechanisms and also having relatively strong relationships with the TPB constructs of attitude and subjective norm. In a 2018 study of pedestrian traffic violations (e.g., jaywalking), the willingness variable had a much stronger effect on behavior (r = .51) than the intention variable (r = .10), and willingness was also found to predict intention when alternative structural equation models were compared. In that study, the effect of perceived behavioral control was also partially mediated by willingness, suggesting that even one of the original TPB constructs might be accounted for by looking at Intuitive-system mechanisms involving willingness. By the time that collinearity among the effects was taken out of the equation, the TPB attitude and subjective norm constructs had hardly any effect at all, even on intentions. The authors conclude that social-reactive mechanisms expressed in the PWM are much more useful in predicting pedestrians' unsafe behaviors than the reasoned-action mechanisms involved in the TPB. Overall, then, recent research continues to support the conclusion that PWM constructs can augment the TPB, and in at least one case the PWM constructs seem to have much more explanatory value than the original TPB constructs, to the extent that the original constructs are no longer necessary for the model.
With the addition of PWM constructs connected to the Intuitive Mind, I'm more optimistic than I was before about the future of the TPB. I can see several interesting directions for research: First, as suggested above, it would be helpful to collect some data on this updated model using daily survey methods that get closer to the actual time of behavior, and thereby help to filter out some of the static from Narrative-Mind interpretations of behavior. Second, there's some interesting work to be done on the construct of perceived behavioral control, which seems to predict both willingness and intention. Maybe this is because willingness is really measured as a prediction of future behavior, and a person's sense of how much control they have over their behavior factors into that prediction? Perceived control also still seems to have its direct effect on behavior, even after accounting for proposed mediators from both the PWM and the TPB. Finally, it would be useful to have more meta-analytic work on the relative contributions of TPB and PWM constructs in predicting behavior, in both adolescents and adults. It seems possible based on some of the findings that the TPB constructs will simply fall out of the model once the PWM constructs are accounted for. At that point, the PWM might look more like a completely new model of behavior, rather than a modification of an existing one.
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