Predicting and explaining intentions and behavior: How well are we doing?

Meta-analyses of research using the theory of reasoned action (TRA) and the theory of planned behavior (TPB) show that these models explain on average between 40% and 50% of the variance in intention, and between 19% and 38% of the variance in behavior. This paper evaluates the performance of these models in predicting and explaining intentions and behavior. It discusses the distinction between prediction and explanation, the different standards of comparison against which predictive performance can be judged, the use of percentage of variance explained as a measure of effect size, and presents 9 reasons why the models do not always predict as well as we would like them to do.