Research dealing with various aspects of the theory of planned behaviour (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 behaviours of different kinds can be predicted with high accuracy from attitudes toward the behaviour, subjective norms and perceived behavioural control; and these intentions, together with perceptions of behaviour control, account for considerable variance in actual behaviour. Attitudes, subjective norms and perceived behavioural control are shown to be related to appropriate sets of salient behaviour, normative and control beliefs about the behaviour, 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 behaviour 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 behaviour quite well in comparison to the ceiling imposed by behavioural reliability.

As every student of psychology knows, explaining human behaviour 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 behaviour. Concepts referring to behaviour dispositions, such as social attitude and personality trait, have played an important role in these attempts to predict and explain human behaviour (see Ajzen, 1988; Campbell, 1963; Sherman and Fazio, 1983). Various theoretical frameworks have been proposed to deal with the psychological processes involved. This special edition of Organizational Behaviour and Human Decision Processes concentrates on cognitive self-regulation as an important aspect of human behaviour.


Much has been made of the fact that general dispositions tend to be poor predictors of behaviour 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 and Fishbein, 1977, for a literature review). The failure of such general attitudes to predict specific behaviours directed at the target of the attitude has produced calls for abandoning the attitude concept (Wicker, 1969).

In a similar fashion, the low empirical relations between general personality traits and behaviour in specific situations has led theorists to claim that the trait concept, defined as a broad behaviour disposition, is untenable (Mischel, 1968). Of particular interest for present purposes are attempts to relate generalized locus of control (Rotter, 1954, 1966) to behaviours in specific contexts. As with other personality traits, the results have been disappointing. For example, perceived locus of control, as assessed by Rotter's scale, often fails to predict achievement-related behaviour or political involvement in a systematic fashion; and somewhat more specialized measures, such as health-locus of control and achievement-related locus of control, have not fared much better.

One proposed remedy for the poor predictive validity of attitudes and traits is the aggregation of specific behaviours across occasions, situations and forms of action. The idea behind the principle of aggregation is the assumption that any single ample of behaviour reflects not only the influence of a relevant general disposition but also the influence of various other factors unique to the particular occasion, situation and action being observed. By aggregating different behaviours, observed on different occasions and in different situations, these other sources of influence tend to cancel each other, with the result that the aggregate represents a more valid measure of the underlying behavioural disposition than any single behaviour. Many studies performed in recent years have demonstrated the workings of the aggregation principle by showing that general attitudes and personality traits do in fact predict behavioural aggregates much better than they predict specific behaviours, (see Ajzen, 1988, for a discussion of the aggregation principle and for a review of empirical research.)

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