Self-Identity and Purchase Intention: an Extension of the Theory of Planned Behaviour

ABSTRACT - To verify the influence of self-identity on purchase intention within the framework of the Theory of Planned Behaviour (Ajzen 1985, 1991) a research project was carried out. Two pre-tests and a main study were conducted ascertaining self-identity by using the self-schemata related to Abeing trendy@. Results showed that self-identity influences purchase intention in two distinct ways: directly, independently from the other behavioural determinants; and indirectly, through the behavioural beliefs related to the schemata with which self-identity has been defined.

Citation:

Stefano Puntoni (2001) ,"Self-Identity and Purchase Intention: an Extension of the Theory of Planned Behaviour", in E - European Advances in Consumer Research Volume 5, eds. Andrea Groeppel-Klien and Frank-Rudolf Esch, Provo, UT : Association for Consumer Research, Pages: 130-134.

European Advances in Consumer Research Volume 5, 2001      Pages 130-134

SELF-IDENTITY AND PURCHASE INTENTION: AN EXTENSION OF THE THEORY OF PLANNED BEHAVIOUR

Stefano Puntoni, Londong Business School, United Kingdom

ABSTRACT -

To verify the influence of self-identity on purchase intention within the framework of the Theory of Planned Behaviour (Ajzen 1985, 1991) a research project was carried out. Two pre-tests and a main study were conducted ascertaining self-identity by using the self-schemata related to "being trendy". Results showed that self-identity influences purchase intention in two distinct ways: directly, independently from the other behavioural determinants; and indirectly, through the behavioural beliefs related to the schemata with which self-identity has been defined.

In consumer behaviour literature several studies have regarded the analysis of the influence of self-identity on purchase intention and product preference (e.g., Aaker 1999; Graeff 1996; Landon 1974; Malhotra 1988; Sirgy 1982; Sirgy and Johar 1999). However, they have offered only an incomplete framework. None of them has conducted the discussion within a comprehensive model of the determinants of intention.

The Theory of Reasoned Action (Fishbein and Ajzen 1975) - and its recent development, the Theory of Planned Behaviour (Ajzen 1985, 1991) - are two models for the analysis of behavioural intention originating from social psychology and widely used in marketing contexts (e.g., Bagozzi, Baumgartner and Yi 1992; Bagozzi and Warshaw 1990; Caprara, Barbaranelli and Guido 1998; Notani 1997; Sheppard, Hartwick and Warshaw 1988). The purpose of this study is to test, within the framework of the Theory of Planned Behaviour, the existence of a significant effect of self-identity on purchase intention.

In this research self-identity is defined as the salient part of an actor’s self related to a particular behaviour, coherently with Conner and Armitage (1998) and Sparks and Guthrie (1998).

Following the approach employed by Aaker (1999), self-identity referred to a behaviour could be defined through the self-schemata related to that behaviour (Markus 1977). Given that socially visible products reveal users’ personal characteristics more than products not consumed in a social context, self-identity is likely to be a better predictor of intention and attitudes in the first case rather than in the latter (Sirgy and Johar 1999). Wanting to conduct the survey with products of large diffusion characterized by a social consumption, a suitable way to assess the effect of self-identity was therefore identified in the use of the schematic information related to "being trendy".

Contrary to what has been assumed by previous contributions dedicated to the analysis of the impact of self-identity on behavioural intention (e.g., Biddle, Bank and Slavings 1987; Charng, Piliavin and Callero 1988; Granberg and Holmberg 1990), we propose that the effect of self-identity is dichotomous in nature. According to this hypothesis, self-identity influences intention both directly, i.e. independently from the other behavioural determinants; and indirectly, i.e. through attitudes, and specifically through those behavioural beliefs that are related to the schemata with which self-identity has been defined.

RELEVANT LITERATURE AND HYPOTHESES

The Theory of Planned Behaviour

The purpose of the Theory of Reasoned Action (Fishbein and Ajzen 1975), hereafter TRA, and of the Theory of Planned Behaviour (Ajzen 1985, 1991), hereafter TPB, is the prediction and explanation of behaviour. The models assume that the proximal cause of behaviour is the intention to engage in that behaviour. According to the TRA, intentions are, in turn, functions of two variables: attitudes towards the behaviour (Ab) and subjective norm (SN), a factor of social pressure. Subjective norm represents the pressure generated by relevant "others" with respect to that behaviour.

The TPB postulates that in addition to these two predictors, in the study of non volitional behaviours, another factor, called the perceived behavioural control, is a significant determinant of intention and behaviour. The perceived behavioural control (PBC) represents the person’s beliefs as to how easy or difficult performance of the behaviour is likely to be (Ajzen and Madden 1986). Both the TRA and the TPB belong to the family of models called "expectancy-value" models. Therefore attitudes, subjective norm and perceived behavioural control are functions, respectively, of behavioural beliefs, normative beliefs and control beliefs, and of their evaluation, respectively: outcome evaluation, motivation to comply, and perceived power. To obtain an estimate of the determinants of intention, each salient belief must be multiplied by its evaluation, and then all these products must be summed (Fishbein and Ajzen 1975). To determine attitudes, for example, the most important consequences of the behaviour must firstly be identified through a pilot study. Secondly, in the main questionnaire two questions must be included for each of these consequences: "How likely is that Y occurs as a consequence of the behaviour X?" (representing the estimation of the behavioural belief Y) and "How important for you is the occurrence of the consequence Y?" (representing the outcome evaluation for the belief Y). Multiplying the results of these two questions and then adding all the products obtained in correspondence to each selected belief, we reach an indirect measure of attitudes.

Self-identity and the Theory of Planned Behaviour

In social psychology various studies have attempted to extend the determinants of behavioural intention postulated by the TRA or the TPB by including a measure of self-identity (e.g., Armitage, Conner and Norman 1999; Biddle et al. 1987; Charng et al. 1988; Granberg and Holmberg 1990; Sparks and Guthrie 1998; Sparks and Shepherd 1992).

These contributions suggest that self-identity has a significant effect on intention. The size of this effect varies with the behaviour investigated. The meta-analysis by Conner and Armitage (1998) recognises self-identity to be an independent predictor of intention, even controlling the effect of the other determinants postulated by the TPB. In the meta-analysis self-identity appears to explain in average 1% of the variance of intention. Armitage et al. (1999) have found evidence of a stronger effect. These authors investigated the significance of this construct in the explanation of intention together with the effect of mood on information processing. In a food choice context, self-identity was much more significant than attitudes in explaining intention (under positive mood condition for self-identity b=0.80, whereas for attitudes b=0.19; under negative mood condition for self-identity b=0.50, whereas for attitudes b=0.38).

With regards to the behavioural domain considered in this research, the purchase of products characterised by social consumption, like clothing, represents a common means of expression of the self. As noted by Ericksen and Sirgy (1992), in fact, "researchers have found that clothing is important in the perception of others (...), that is indicative of role (...), and that it creates a symbolic image (...). Therefore, it is an expression of personality and of self " (p. 408).

Shavitt and Fazio (1991) maintain, in a study about the way in which the salience of the attributes employed in the definition of attitudes influences the relationship between attitudes and intention, that "in evaluating an object that is perceived to create a particular social impression (e.g. trendy clothing, ...), attributes related to that social impression may be naturally salient and drive one’s evaluation" (p. 508).

Almost all the authors who assessed the effect of self-identity within the context of the TPB attributed to this construct an independent effect on intention (e.g., Biddle et al. 1987; Charng et al. 1988) or on behaviour (Granberg and Holmberg 1990). For example, Biddle et al. (1987) wrote: "although the assumption of consistency between self-identity labels and other cognition may sometimes be warranted, this is certainly not always the case. One can think of examples likely to be characterised by the following reasoning: I would enjoy doing A (...) but I am the type of person more oriented to doing C" (p. 326, Italic added).

Despite the evidence of a direct effect of self-identity on intention, Sparks and Shepherd (1992) are sceptical about the theoretical rationale at the grounds of its definition. They hypothesised that self-identity would influence attitudes but were unable to empirically demonstrate the existence of a mediational effect of attitudes. By finding a significant effect of self-identity in the prediction of brand attitude, Sirgy and Johar (1999) offered such evidence.

Hypotheses

We hypothesise that the mechanism with which self-identity influences purchase intention is that suggested by the self-congruence hypothesis (Sirgy 1982), that stats that purchase intention towards a certain product may be weaker or stronger depending on the amount of felt identification towards the image of the product, since such an identification leads to the satisfaction of the need for self-consistency (Sirgy and Johar 1999). The emergence of a relationship between purchase intention and the schemata related to the model that the product suggests is therefore possible, thanks to the presence of a contextual congruence between the image of the product and that of the self.

We contend that the effect of self-identity on purchase intention is dichotomous in nature. Self-identity is hypothesised to exert its influence on intention both independently from the other behavioural determinants and through those behavioural beliefs related to the schemata employed in the definition of self-identity.

According to Eagly and Chaiken (1993), the effect of self-identity could be subsumed under attitudes towards the behaviour because the outcomes of meeting or violating one’s self-concept are consequences of the behaviour. Yet the independent effect of self-identity on intention, shown in the studies listed above, even controlling the effect of the other determinants postulated by the TPB, leads to the following hypothesis:

H1: Self-identity towards the image of a product directly affects purchase intention towards that product.

As maintained by Shavitt and Fazio (1991), moreover, we hypothesise that self-identity labels would influence attitude - and then intention - through the behavioural beliefs related to the social model employed in the definition of those labels:

H2: Self-identity towards the image of a product affects purchase intention towards that product through its influence on the behavioural beliefs related to the schemata employed in the definition of self-identity.

The rationale behind this hypothesis is intuitive. Coherently with the self-congruence hypothesis (Sirgy 1982), depending on the extent to which a certain aspect of the self is important for a person, the more an object is perceived to contribute to enhance that aspect of the self - i.e. the higher the behavioural beliefs related to the object -, the higher will be the purchase intention towards that object.

Hypotheses H1 and H2 together suggest a mediational model of the relationship between self-identity and purchase intention (Baron and Kenny 1986). In such model, the behavioural beliefs linked to the schemata employed in the definition of self-identity, i.e. in our context related to "being trendy", act as mediator. These behavioural beliefs therefore "explain how external physical events take an internal psychological significance" (Baron and Kenny 1986, p. 1176).

METHOD

Sample and procedure

A branded product was chosen on the basis of a pilot study in which 85 undergraduate Italian students were asked to express their general attitudes towards a list of 10 branded products and their perception of the strength of the image of each brand. The branded products were: Adidas sport clothing, Calvin Klein perfumes, Diesel jeans, Hewlett-Packard calculator, Lacoste clothing, Levi’s jeans, Motorola mobile phone, Ray Ban sunglasses, Sony playstation and Swatch watches. The test clearly showed that Levi’s jeans was the brand with the highest score on both the requirements (attitude and brand image strength).

In a further pre-test with 35 undergraduate students we elicited the most salient beliefs regarding this brand for all the constructs included in the TPB, using the methodology proposed by Ajzen and Fishbein (1980) and widely employed in the literature.

The data for the main study was collected from Italian undergraduate students. The total sample size was 204, 54% male and 46% female (mean age=22.19, s.d.=1.94).

Questionnaire

According to the principle of compatibility (Ajzen and Fishbein 1977) the behaviour investigated was defined with respect to the four characteristics of every behaviour, as postulated by Ajzen and Fishbein (1977): action, target, context and time. We defined the behaviour as the purchase (action) of a pair of Levi’s jeans (target) in the three months after the experiment (time), therefore posing no constraints on context which is the norm for this kind of research (see, e.g., Caprara et al. 1998).

To measure the self-identity towards "being trendy" we used the methodology employed in the domain of green consumerism by Sparks and Shepherd (1992), Sparks and Guthrie (1998) and Armitage et al. (1999). The items were "I regard myself as a person preoccupied with always being in expensive and high quality clothing", "I think of myself as a person who is very concerned with the care of his clothes", "I think of myself as a trendy person".

The questionnaire contained 10 items for the measurement of attitudes towards the behaviour (5 behavioural beliefs and 5 evaluation of consequences), 6 for subjective norm (3 subjective norms and 3 motivations to comply), and 16 for perceived behavioural control (8 control beliefs and 8 perceived power). Intention has been measured by the means of 2 items ("How strong is your intention to buy a pair of Levi’s jeans in the next three months?", "Evaluate the likelihood that in the next three months you decide to buy a pair of Levi’s jeans").

TABLE 1

HIERARCHICAL REGRESSION OF PURCHASE INTENTION

TABLE 2

CORRELATION BETWEEN SI AND BEHAVIOURAL BELIEFS

Results

The observed level of Cronbach's alpha for the items about intention and self-identity is, respectively, 0.92 and 0.71. The data was analysed by the means of hierarchical regression, a methodology widely employed testing the TPB (e.g., Ajzen and Madden 1986; Armitge et a]. 1999; Fishbein and Stasson 1990; Sparks and Guthrie 1998).

In the first step attitudes (Ab), subjective norm (SN) and perceived behavioural control (PBC) were entered. In the second step self-identity (SI) was added to the previous predictors (Table 1).

By far the most significant predictor is PBC. Results show that self-identity has a significant, but not very strong, effect on purchase intention even after taking into account the other variables.

Introducing gender into the model, as expected for this product, this variable turns out to be a significant predictor of intention (0=-0.255, p<0.01) [The value zero was attributed to male subjects.]. In fact, the personality of Levi's is strongly characterised by a factor called "ruggedness" by Aaker (1997). This latent dimension is defined by adjectives such as "tough", "masculine", "outdoorsy", "rugged" and characterises brands such as Levi's, Marlboro, Nike and Harley-Davidson (Aaker 1997). We expect, therefore, the level of felt identification towards the model synthesized by Levi's jeans to be much stronger for males than for females, i.e. we expect gender to moderate the relationship between self-identity and behavioural intention. We then conducted another hierarchical regression splitting the sample according to gender. In the case of male subjects, self-identity was more significant than in the complete dataset (0=0.260, p<0.01) - as significant as PBC. Moreover, for male subjects multiple R was higher than that reported in Table 1 (0.579). For female subjects, on the contrary, SI was non significant at the level 0.05 and multiple R much lower than that observed for male subjects. These results strongly support the conclusions of Aaker (1997) about the nature of the personality of Levi's as well as the significance of self-identity in the prediction of purchase intention for male subjects, hence they strengthen the acceptance of HI.

Regarding the test of H2, Table 2 contains the correlations between self-identity and the salient behavioural beliefs selected within the second pilot study and employed in the main questionnaire - representing the subjective estimation of the consequences deriving from the purchase of a pair of Levi's jeans. The variable included in the analysis, for each behavioural belief considered, was the product between the belief and its evaluation.

For the total sample the correlation between the belief related to the self-schemata used in the definition of self-identity (B1) is more than twice the correlation between self-identity and the others beliefs. In particular, the correlation between SI and B1 is very strong for male subjects (0.63).

Nevertheless, the correlation between self-identity and attitudes, calculated as the sum of the expectancy-value products associated to each belief is weak (0.137). This is due to the fact that B1 is the least significant belief among those considered. In fact, the mean values for each belief listed in Table 2 are respectively: 14.77 (s.d. 10.98); 33.72 (s.d. 12.89); 22.82 (s.d. 12.54); 32.30 (s.d. 12.73); and 29.83 (s.d. 14.55). This means that being trendy as a result of the purchase of a pair of Levi’s jeans was perceived by the subjects as the least significant among the consequences selected for the main study. The weak correlation between SI and attitudes is, therefore, due to the low level of salience of B1.

To test the mediational model implied by the research hypotheses, we examined the significance of the mediation of the behavioural belief related to "being trendy" (B1) on the relationship between SI and purchase intention using the methodology described by Baron and Kenny (1986). Recently, the appropriateness of this methodology has also been underlined by Lehmann (2001).

SI is highly significant in explaining both the mediator variable (B1) and the dependent variable (intention). (In the first regression ¯=0.595, p<0.001 and in the second ¯=0.259, p<0.001). Moreover, including B1 in the regression of intention on SI, the significance of SI decreases considerably (¯ from 0.259 to 0.174, p from <0.001 to 0.04). The behavioural belief related to "being trendy" therefore acts as mediator of the relationship between SI and intention. Such conclusion still holds repeating the analysis considering instead of B1 (the multiplication between the behavioural belief and its evaluation) only the behavioural belief. These results lead to the acceptance of H2.

DISCUSSION

The results obtained are consistent with both research hypotheses and show that, in the particular context of application chosen, self-identity represents a useful predictor of purchase intention. Although significant, especially for male subjects, the strength of the direct effect of this construct on intention is not very strong (F_change significant at the level of 0.05 but not at that of 0.01). In their meta-analysis Conner and Armitage (1998) observed a stronger effect. However, the motivation associated with the behavioural domain investigated in this research is, usually, less intense than that related to the behaviours considered in the meta-analysis by Conner and Armitage (1998) - e.g. blood donation (Charng et al. 1988), or quitting college before finishing (Biddle et al. 1987) - and therefore this result was to be expected.

Concerning the original structure of the model, the research confirms the predictive power of attitudes and, especially, of the perceived behavioural control. As expected for the type of behaviour investigated, subjective norm was not significant. The definition of the determinants of intention made through the "expectancy-value" formulation appears to be a very useful approach, making possible a wide range of analyses of the mechanisms that lead to the formation of purchase intention.

Further research is needed to assess the role of gender in the determination of the link between self-identity and purchase intention. The study should be repeated using subjects belonging to other population segments and different categories of products, such as low involvement goods. The construct of involvement seems indeed to be linked to that of self-identity: the higher the felt identification towards the image of a product, the higher the involvement of the subject towards the purchase of that product. Further research is needed to verify the existence of a proportional link between the levels of the two constructs.

Conclusions

The purpose of the research was to verify, within the framework provided by the Theory of Planned Behaviour (Ajzen 1985, 1991), the existence of a significant relationship between self-identity and purchase intention, as well as to identify the mechanism that exerts such an effect.

A research project characterised by two pre-tests and a main study was carried out. Levi’s jeans was used as the stimulus product and self-identity was ascertained by using the self-schemata related to "being trendy".

From an analysis of past research two different ways of interpreting the relationship between self-identity and behavioural intention emerge. The first one singles out a direct effect of self-identity not mediated by other variables (e.g., Charng et al. 1988; Biddle et al. 1987), whereas the second claims the existence of a mediating effect of attitudes (e.g., Sparks and Shepherd 1992). Instead of assuming one of these two views, we proposed that the relationship between self-identity and purchase intention is dichotomous in nature.

Results were consistent with both hypotheses and suggest that self-identity influences purchase intention in two distinct ways: directly, independently from the other behavioural determinants; and indirectly, through attitudes, and specifically through those behavioural beliefs related to the schemata with which self-identity has been defined.

From a broader perspective, this research confirms the need, in the study of purchase intention, for considering structural factors linked to the personality of the consumer together with the cognitive processes represented by the determinants included in the TPB.

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