Principal findings

The aim of this study was to investigate the determinants of sustainable purchasing behaviour and to generate valuable insights for social entrepreneurs and policy makers to enhance their ability to promote sustainable consumer behaviour. The research questions associated with this aim were: What is the relationship between self-interest and sustainable purchasing behaviour of Dutch consumers? What is the role of age and gender on this relationship? Is the relationship between self-interest and sustainable purchasing behaviour mediated by status consumption, and what is the role of materialism on this indirect effect?

Firstly, the main hypothesis stated that there is a positive relationship between self-interest and sustainable purchasing behaviour, such that a higher level of self-self-interest, results in a higher level of sustainable purchasing behaviour. In this study, self-interest was measured as the inverted value of altruism, as it was assumed that these concepts are opposites of each other. The correlation matrix showed a small positive correlation between altruism and sustainable purchasing behaviour (r = 0.10, p < 0.05). This relationship was further investigated by conducting a regression analysis.

The regression analysis showed that altruism predicts sustainable purchasing behaviour in a positive way (F(1, 475) = 5.28, p < .05), specifically that if altruism increases by one point on a 5-point Likert scale, it results in an increase in sustainable purchasing behaviour by 0.175 points. This suggests a negative relationship between self-interest and sustainable purchasing behaviour. However, since hypothesis one indicated a positive relationship between self-interest and sustainable purchasing behaviour, this hypothesis was rejected. This finding contradicts the current literature, where it was found that self-interest positively influences sustainable purchasing behaviour since caring for the environment benefits egoistic consumers (De Dominicis et al., 2017; Schradin, 2022). This was suggested since this increases their

fitness, linking it back to the evolutionary bases of behaviour (Griskevicius et al., 2012).

Therefore, this finding contradicts the current literature on this sustainability topic.

However, it can also be a possibility that both relationships are positive, not only the relationship between altruism and sustainable purchasing behaviour but also with self-interest as predictor. Since altruism is revolved around putting other interests above your own, this can also imply prioritizing the needs of the planet over your own needs. Or, for instance, putting the interests of future generations above your own interests. Both of these options demonstrate altruistic behaviour that would result in sustainable purchasing behaviour. Whereas for self-interested individuals, there are other reasons to engage in sustainable purchasing behaviour.

One of them is to gain status or to ensure their own future on this planet. Therefore, the possibility of a positive relationship between self-interest and sustainable purchasing behaviour cannot be ruled out. However, a reliable scale to measure the direct effect of self-interest was not present in the literature.

This reasoning can be supported by exploring the literature regarding the differences between altruism and self-interest in the context of sustainability. Altruism can be seen as “the condition under which the consumer acts on another’s behalf without expecting any type of benefit” (Uddin & Khan, 2018, p. 272). Whereas a self-interested individual will focus on the consequences for themselves when considering a certain behaviour (Clark et al., 2003). Since these two concepts are opposites, it was assumed that a positive relationship between altruism and sustainable purchasing behaviour would reflect a negative relationship between self-interest and sustainable purchasing behaviour, as depicted in the literature (De Dominicis et al., 2017). Where the motive for altruistic consumers might be caring for the planet, for self-interested people this could also be of benefit since this means protecting their future (De Dominicis et al., 2017). Thus, further research is necessary to clearly outline the relationship between self-interest and sustainable purchasing behaviour.

Secondly, hypothesis 2a stated that the positive relationship between self-interest and sustainable purchasing behaviour is moderated by age, such that this relationship is stronger for younger levels of age. The moderation analysis found no significant interaction effect for age as a moderator (b = -.007, p = .178). This is not in line with the literature on the moderating effect of age on the relationship between self-interest and sustainable purchasing behaviour.

According to the literature, younger consumers have a higher level of status consumption (Eastman & Liu, 2012). This implied that the effect of self-interest on sustainable purchasing behaviour would be stronger for younger consumers, since self-interested individuals would have a need for prestige. However, this study did not find a moderating effect of age, thus, hypothesis 2a was rejected.

Nonetheless, an interesting finding was that age has a significant direct relationship with sustainable purchasing behaviour, specifically when a Dutch consumer increases one year in age, sustainable purchasing behaviour increases by 0.048 on a 7-point Likert scale (b = 0.048, p < 0.05). This is in line with the literature, since Casalegno et al. (2022) indeed found that older people buy more eco-friendly and sustainable products. Thus, the older the buyer, the higher the sustainable purchasing behaviour. Moreover, this complements the findings of Wiernik et al. (2013), who also found an increased concern for nature, avoiding harm by engaging in sustainable purchasing behaviour.

A second moderation analysis was conducted to investigate hypothesis 2b. This depicts the moderating effect of gender on the relationship between self-interest and sustainable purchasing behaviour, such that this relationship is stronger for men and weaker for women.

The moderation analysis found no support for a moderating role of gender (b = .269, p = .193), rejecting hypothesis 2b. This is not in line with the literature since Roux et al. (2017) found that the desire for uniqueness and status consumption positively influences exclusivity and

elitism for men. Therefore, it was expected that the desire for prestige, a self-interested motive for sustainable purchasing behaviour, was strengthened for men rather than for women.

In addition, this study investigated a moderated mediation model, with hypothesis 3 being that the positive relationship between self-interest and sustainable purchasing behaviour is mediated by status consumption. However, the mediation analysis using the PROCESS macro by Hayes (2018) showed no significant results for a mediation effect of status consumption on the relationship between self-interest and sustainable purchasing behaviour (b

= -.001, 95% CI = -.013, .010). Since the 95% confidence interval shows that this indirect effect is not statistically different from zero, it can be implied that hypothesis 3a was rejected. This is not in line with the literature, which stated that egoistic drivers of sustainable purchasing behaviour are to obtain status (Schradin, 2022). When someone is self-interested, their behaviour will correspond to actions that benefit themselves. One of these benefits is to gain status (Clark et al., 2003; Tascioglu et al., 2017). Therefore, a positive relationship between self-interest and status motivation was expected, as well as a positive relationship between status motivation and sustainable purchasing behaviour. Since sustainable purchasing can be used as a way to demonstrate status. (Eastman & Iyer, 2021; Tascioglu et al., 2017).

Hypothesis 3b stated that the positive relationship between status consumption and sustainable purchasing behaviour is moderated by materialism, such that this relationship is stronger for higher values of materialism. However, the moderation analysis showed no signification moderation effect of materialism on the relationship between status consumption and sustainable purchasing behaviour (b = .40, p = .744) This study, therefore, contradicts the findings of Tascioglu et al. (2017), who found that materialism can in fact act as a moderator between status motivation and sustainable consumer behaviour. Furthermore, it is not in line with the findings of Goldsmith and Clark (2012), as well as Talukdar and Yu (2020) and Kaur

et al. (2022) who all found that high materialism strengthens the purchase intention of sustainable luxury products because of the status attained when buying a luxury product.

Regarding the total moderated mediation as proposed in this study, which means that the positive relationship between self-interest and sustainable purchasing behaviour through mediator status consumption is moderated by materialism; it cannot be concluded that there is a moderated mediation on the relationship between self-interest and sustainable purchasing behaviour (b = .031, p = .801). This contradicts the literature on the different relationships of this model, as described above.