Predicting Intentions: Attitudes, Subjective Norms and Perceived Behavioural Control

The theory of planned behaviour postulates three conceptually independent determinants of intention. The first is the attitude toward the behaviour and refers to the degree to which a person has a favourable or unfavourable evaluation or appraisal of the behaviour in question. The second predictor is a social factor termed subjective norm; it refers to the perceived social pressure to perform or not to perform the behaviour. The third antecedent of intention is the degree of perceived behavioural control which, as we saw earlier, refers to the perceived ease or difficulty of performing the behaviour and it is assumed to reflect past experience as well as anticipated impediments and obstacles. As a general rule, the more favourable the attitude and subjective norm with respect to a behaviour and the greater the perceived behavioural control, the stronger should be an individual's intention to perform the behaviour under consideration. The relative importance of attitude, subjective norm and perceived behavioural control in the prediction of intention is expected to vary across behaviours and situations. Thus, in some applications it may be found that only attitudes have a significant impact on intentions, in others that attitudes and perceived behavioural control are sufficient to account for intentions and in still others that all three predictors make independent contributions.

Planned Behaviour.

Fig. 14.15: Planned Behaviour.


True to its goal of explaining human behaviour, not merely predicting it, the theory of planned behaviour deals with the antecedents of attitudes, subjective norms and perceived behavioural control, antecedents which in the final analysis determine intentions and actions. At the most basic level of explanation, the theory postulates that behaviour is a function of salient information, or beliefs, relevant to the behaviour. People can hold a great many beliefs about any given behaviour, but they can attend to only a relatively small number at any given moment. It is these salient beliefs that are considered to be the prevailing determinants of a person's intentions and actions. Three kinds of salient beliefs are distinguished: behavioural beliefs which are assumed to influence attitudes toward the behaviour, normative beliefs which constitute the underlying determinants of subjective norms and control beliefs which provide the basis for perceptions of behavioural control.

Behavioural Beliefs and Attitudes toward Behaviours

Most contemporary social psychologists take a cognitive or information-processing approach to attitude formation. This approach is exemplified by Fishbein and Ajzen's (1975) expectancy-value model of attitudes. According to this model, attitudes develop reasonably from the beliefs people hold about the object of the attitude. Generally speaking, we form beliefs about an object by associating it with certain attributes, i.e., with other objects, characteristics, or events. In the case of attitudes toward a behaviour, each belief links the behaviour to a certain outcome, or to some other attribute such as the cost incurred by performing the behaviour. Since the attributes that come to be linked to the behaviour are already valued positively or negatively, we automatically and simultaneously acquire an attitude toward the behaviour. In this fashion, we learn to favor behaviours we believe have largely desirable consequences and we form unfavourable attitudes toward behaviours we associate with mostly undesirable consequences. Specifically, the outcome's subjective value contributes to the attitude in direct proportion to the strength of the belief, i.e., the subjective probability that the behaviour will produce the outcome in question. As shown in Eq. (1), the strength of each salient belief (b) is combined in a multiplicative fashion with the subjective evaluation (e) of the belief's attribute and the resulting products are summed over the n salient beliefs. A person's attitude (A) is directly proportional (") to this summative belief index.

We can explore an attitude's informational foundation by eliciting salient beliefs about the attitude object and assessing the subjective probabilities and values associated with the different beliefs. In addition, by combining the observed values in accordance with Eq. (1), we obtain an estimate of the attitude itself, an estimate that represents the respondent's evaluation of the object or behaviour under consideration. Since this estimate is based on salient beliefs about the attitude object, it may be termed a belief-based measure of attitude. If the expectancy-value model specified in Eq. (1) is valid, the belief-based measure of attitude should correlate well with a standard measure of the same attitude.

A great number of studies have, over the years, tested the general expectancy-value model of attitude as well as its application to behaviour. In a typical study, a standard, global measure of attitude is obtained, usually by means of an evaluative semantic differential and this standard measure is then correlated with an estimate of the same attitude based on salient beliefs (e.g., Ajzen, 1974; Fishbein, 1963, Fishbein and Ajzen, 1981; Jaccard and Davidson, 1972; Godin and Shephard, 1987; Insko, Blake, Cialdini and Mulaik, 1970; Rosenberg 1956). The results have generally supported the hypothesized relation between salient beliefs and attitudes, although the magnitude of this relation has sometimes been disappointing.

Various factors may be responsible for relatively low correlations between salient beliefs and attitudes. First, of course, there is the possibility that the expectancy-value model is an inadequate description of the way attitudes are formed and structured. For example, some investigators (e.g., Valiquette, Valois, Desharnais and Godin, 1988) have questioned the multiplicative combination of beliefs and evaluations in the expectancy-value model of attitude. Most discussions of the model, however, have focused on methodological issues

Belief salience.

It is not always recognized that the expectancy-value model of attitude embodied in the theories of reasoned action and planned behaviour postulates a relation between a person's salient beliefs about the behaviour and his or her attitude toward that behaviour. These salient beliefs must be elicited from the respondents themselves, or in pilot work from a sample of respondents that is representative of the research population. An arbitrarily or intuitively selected set of belief statements will tend to include many associations to the behaviour that are not salient in the population and a measure of attitude based on responses to such statements need not correlate highly with a standard measure of the attitude in question. Generally speaking, results of empirical investigations suggest that when attitudes are estimated on the basis of salient beliefs, correlations with a standard measure tend to be higher than whey they are estimated on the basis of an intuitively selected set of beliefs. Nevertheless, as we will see below, correlations between standard and belief-based measures are sometimes of only moderate magnitude even when salient beliefs are used.

Optimal scaling.

A methodological issue of considerable importance that has not received sufficient attention has to do with the scaling of belief and evaluation items. In most applications of the theory of planned behaviour, belief strength is assessed by means of a 7-point graphic scale (e.g., likely-unlikely) and evaluation by means of a 7-point evaluative scale (e.g., good-bad). There is nothing in the theory, however, to inform us whether responses to these scales should be scored in a unipolar fashion (e.g., from 1 to 7, or from 0 to 6) or in a bipolar fashion (e.g., from -3 to +3). Belief strength (b) is defined as the subjective probability that a given behaviour will produce a certain outcome. In light of this definition, it would seem reasonable to subject the measure of belief strength to unipolar scoring, analogous to the 0 to 1 scale of objective probabilities. In contrast, evaluation (e), like attitudes, are usually assumed to form a bipolar continuum, from a negative evaluation on one end to a positive evaluation on the other (see Pratkanis, 1989, for a discussion of unipolar versus bipolar attitude structures).

From a measurement perspective, however, either type of scoring could be applied with equal justification. Rating scales of the kind used in research on the expectancy-value model can at best be assumed to meet the requirements of equal-interval measures. As such, it is permissible to apply any linear transformation to the respondents, ratings without altering the measure's scale properties. Going from a bipolar to a unipolar scale, or vice versa, is of course a simple linear transformation in which we add or substract a constant from the obtained values.*

There is thus no rational a priori criterion we can use to decide how the belief and evaluation scales should be scored (cf., Schmidt, 1973). A relatively easy solution to this problem was suggested by Holbrook (1977; see also Orth, 1985). Let B represent the constant to be added or substracted in the rescaling of belief strength and E the constant to be added or substracted in the rescaling of outcome evaluations. The expectancy-value model shown in Eq. (1) can then be rewritten as

Expanded, this becomes

and, disregarding the constant BE, we can write

To estimate the rescaling parameters B and E, we regress the standard attitude measure, which serves as the criterion, on Sb,e,-, Sbr and Ze;- and then divide the unstandardized regression coefficients of

and Ze;- by the coefficient obtained for Sb,e,- The resulting value for the coefficient of Ze;- provides a

least-squares estimate of B, the rescaling constant for belief strength and the value for the coefficient of Sb,- serves as a least-squares estimate of E, the rescaling constant for outcome evaluation.

Normative Beliefs and Subjective Norms

Normative beliefs are concerned with the likelihood that important referent individuals or groups approve or disapprove of performing a given behaviour. The strength of each normative belief (n) is multiplied by the person's motivation to comply (m) with the referent in question and the subjective norm (SiV) is directly proportional to the sum of the resulting products across the n salient referents, as in Eq. (2):

A global measure of SN is usually obtained by asking respondents to rate the extent to which "important others" would approve or disapprove of their performing a given behaviour. Empirical investigations have shown that the best correspondence between such global measures of subjective norm and belief-based measures is usually obtained with bipolar scoring of normative beliefs and unipolar scoring of motivation to comply (Ajzen and Fishbein, 1980). With such scoring, correlations between belief-based and global estimates of subjective norm are generally in the range of 0.40 to 0.80, not unlike the findings with respect to attitudes.

Control Beliefs and Perceived Behavioural Control

Among the beliefs that ultimately determine intention and action there is, according to the theory of planned behaviour, a set that deals with the presence or absence of requisite resources and opportunities. These control beliefs may be based in part on past experience with the behaviour, but they will usually also be influenced by secondhand information about the behaviour, by the experiences of acquaintances and friends and by other factors that increase or reduce the perceived difficulty of performing the behaviours in question. The more resources and opportunities individuals believe they possess and the fewer obstacles or impediments they anticipate, the greater should be their perceived control over the behaviour. Specifically, as shown in Eq. (3), each control belief (c) is multiplied by the perceived power (p) of the particular control factor to facilitate or inhibit performance of the behaviour and the resulting products are summed across the n salient control beliefs to produce the perception of behavioural control (PBC). Thus, just as beliefs concerning consequences of a behaviour are viewed as determining attitudes toward the behaviour and normative beliefs are viewed as determining subjective norms, so beliefs about resources and opportunities are viewed as underlying perceived behavioural control.

As of today, only a handful of studies have examined the relation between specific control beliefs and perceived behavioural control (e.g., Ajzen and Madden, 1986). Global assessments of the perceived case or difficulty of engaging in each of the five leisure activities were correlated with belief-based measures of perceived behavioural control. With respect to outdoor running or jogging, for example, control factors included being in poor physical shape and living in an area with good jogging weather. In computing the correlations bipolar scoring was used for control beliefs (c) as well as for the perceived power of the control factor under consideration (p). This scoring proved satisfactory for three of the five activities (mountain climbing, boating and biking), as can be seen by comparing the correlations with and without optimal rescoring (Rows 5 and 4, respectively). With regards to spending time at the beach, the optimal scoring analysis indicated that the perceived power components would better be scored in a unipolar fashion; and with respect to outdoor jogging or running, unipolar scoring would have to be applied to both the ratings of control belief strength and the ratings of the perceived power of control factors.

In conclusion, inquiries into the role of beliefs as the foundation of attitude toward a behaviour, subjective norm and perceived behavioural control have been only partly successful. Most troubling are the generally moderate correlations between belief-based indices and other, more global measures of each variable, even when the components of the multiplicative terms are optimally rescored. Note that responding to the belief and valuation items may require more careful deliberations than does responding to the global rating scales. It is, therefore, possible that the global measures evoke a relatively automatic reaction whereas the belief-related items evoke a relatively reasoned response. Some evidence, not dealing directly with expectancy-value models, is available in a study on the prediction of intentions in the context of the theory of reasoned action (Ellen and Madden, 19%). The study manipulated the degree to which respondents had to concentrate on their ratings of attitudes, subjective norms and intentions with respect to a variety of different behaviours. This was done by presenting the questionnaire items organized by behaviour or in random order and by using a paper and pencil instrument versus a computer-administered format. The prediction of intentions from attitudes and subjective norms was better under conditions that required careful responding (random order of items, computer-administered) than in the comparison conditions.

Our discussion of the relation between global and belief-based measured of attitudes is not meant to question the general ideas that attitudes are influenced by beliefs about the attitude object. This idea is well supported, especially by experimental research in the area of persuasive communication: A persuasive message that attacks beliefs about an object is typically found to produce changes in attitudes toward the object. By the same taken, it is highly likely that persuasive communications directed at particular normative or control beliefs will influence subjective norms and perceived behavioural control. Rather than questioning the ideas that beliefs have a causal effect on attitudes, subjective norms and perceived behavioural control, the moderate correlations between global and belief-based measures suggest that the expectancy-value formulation may fail adequately to describe the process whereby individual beliefs combine to produce the global response. Efforts need to be directed toward developing alternative models that could be used better to describe the relations between beliefs on one hand and the global constructs on the other. In the page below, we consider several other unresolved issues related to the theory of planned behaviour.

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