The Theory of Planned Behavior
ICEK AJZEN University of Massachusetts at Amherst Research dealing with various aspects of* the theory of planned behavior (Ajzen, 1985, 1987) is reviewed, and some unresolved issues are discussed. In broad terms, the theory is found to be well supported by empirical evidence. Intentions to perform behaviors of different kinds can be predicted with high accuracy from attitudes toward the behavior, subjective norms, and perceived behavioral control; and these intentions, together with perceptions of behavioral control, account for considerable variance in actual behavior. Attitudes, subjective norms, and perceived behavioral control are shown to be related to appropriate sets of salient behavioral, normative, and control beliefs about the behavior, but the exact nature of these relations is still uncertain. Expectancy— value formulations are found to be only partly successful in dealing with these relations. Optimal rescaling of expectancy and value measures is offered as a means of dealing with measurement limitations. Finally, inclusion of past behavior in the prediction equation is shown to provide a means of testing the theory*s sufficiency, another issue that remains unresolved. The limited available evidence concerning this question shows that the theory is predicting behavior quite well in comparison to the ceiling imposed by behavioral reliability. © 1991 Academic Press. Inc.
As every student of psychology knows, explaining human behavior in all its complexity is a difficult task. It can be approached at many levels, from concern with physiological processes at one extreme to concentration on social institutions at the other. Social and personality psychologists have tended to focus on an intermediate level, the fully functioning individual whose processing of available information mediates the effects of biological and environmental factors on behavior. Concepts referring to behavioral dispositions, such as social attitude and personality trait, have played an important role in these attempts to predict and explain human behavior (see Ajzen, 1988; Campbell, 1963; Sherman & Fazio, 1983). Various theoretical frameworks have been proposed to deal with the psychological processes involved. This special edition of Organizational Behavior and Human Decision Processes concentrates on cogniI am very grateful to Nancy DeCourville, Richard Netemeyer, Michelle van Ryn, and Amiram Vinokur for providing unpublished data sets for reanalysis, and to Edwin Locke for his comments on an earlier draft of this article. Address correspondence and reprint requests to Icek Ajzen, Department of Psychology, University of Massachusetts, Amherst, MA 01003-0034.
Copyright C 1991 by Academic Press. Inc.
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tive self-regulation as an important aspect of human behavior. In the pages below I deal with cognitive self-regulation in the context of a dispositional approach to the prediction of behavior. A brief examination of past efforts at using measures of behavioral dispositions to predict behavior is followed by presentation of a theoretical model—the theory of planned behavior—in which cognitive self-regulation plays an important part. Recent research findings concerning various aspects of the theory are discussed, with particular emphasis on unresolved issues. DISPOSITIONAL PREDICTION OF HUMAN BEHAVIOR
Much has been made of the fact that general dispositions tend to be poor predictors of behavior in specific situations. General attitudes have been assessed with respect to organizations and institutions (the church, public housing, student government, one*s job or employer), minority groups (Blacks, Jews, Catholics), and particular individuals with whom a person might interact (a Black person, a fellow student). (See Ajzen & Fishbein,...