The theory of planned behaviour distinguishes between three types of beliefs- behavioural, normative and control-and between the related constructs of attitude, subjective norm and perceived behavioural control. The necessity of these distinctions, especially the distinction between behavioural and normative beliefs (and between attitudes and subjective norms) has sometimes been questioned (e.g., Miniard and Cohen, 1981). It can reasonably be argued that all beliefs associate the behaviour of interest with an attribute of some kind, be it an outcome, a normative expectation, or a resource needed to perform the behaviour. It should thus be possible to integrate all beliefs about a given behaviour under a single summation to obtain a measure of the overall behavioural disposition.

The primary objection to such an approach is that it blurs distinctions that are of interest, both from a theoretical and from a practical point of view. Theoretically, personal evaluation of a behaviour (attitude), socially expected mode of conduct (subjective norm) and self-efficacy with respect to the behaviour (perceived behavioural control) are very different concepts each of which has an important place in social and behavioural research. Moreover, the large number of studies on the theory of reasoned action and on the theory of planned behaviour have clearly established the utility of the distinctions by showing that the different constructs stand in predictable relations to intentions and behaviour.

Perhaps of greater importance is the possibility of making further distinctions among additional kinds of beliefs and related dispositions. The theory of planned behaviour is, in principle, open to the inclusion of additional predictors if it can be shown that they capture a significant proportion of the variance in intention or behaviour after the theory's current variables have been taken into account. The theory of planned behaviour in fact expanded the original theory of reasoned action by adding the concept of perceived behaviour control.

Personal or Moral Norms

It has sometimes been suggested that, at least in certain contexts, we need to consider not only perceived social pressures but also personal feelings of moral obligation or responsibility to perform, or refuse to perform, a certain behaviour (Gorsuch and Ortberg, 1983; Pomazal and Jaccard, 1976; Schwartz and Tessler, 1972). Such moral obligations would be expected to influence intentions, in parallel with attitudes, subjective (social) norms and perceptions of behavioural control. There are three unethical behaviours: cheating on a test or exam, shoplifting and lying to get out of taking a test or turning in an assignment on time. It seemed reasonable to suggest that moral issues may take on added salience with respect to behaviours of this kind and that a measure of perceived moral obligation could add predictive power to the model.

Participants in the study completed a questionnaire that assessed the constructs in the theory of planned behaviour, as well as a three-item measure of perceived moral obligation to refrain from engaging in each of the behaviours. Result concerning the theory's ability to predict intentions, averaged across the three behaviours, displays the results of hierarchical regression analyses in which the constructs of the theory of planned behaviour were entered on the first step, followed on the second step by perceived moral obligation. It can be seen that although the multiple correlations in the first step were very high, addition of perceived moral obligation further increased the explained variance by 3 to 6%, making a significant contribution in the prediction of each intention.

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