**1. Introduction**

Researchers have identified many negative consequences of materialism. Materialists, compared to non-materialists, are less happy [1,2], have less satisfying social and family relationships [3], are less satisfied with their health and physical condition [4], are more anti-environmental [5], and experience financial problems more often [6]. Since materialism can be a threat to psychological health, it can be considered a public health problem [7]. According to self-determination theory (SDT), materialism negatively affects well-being because it leads to the pursuit of external aspirations (e.g., financial success). These aspirations do not directly fulfill intrinsic aspirations (e.g., social affiliation), which are crucial for well-being [8]. Therefore, practicing activities aimed at fulfilling internal needs should weaken the focus on external, materialistic aspirations. Such activities can include acts of kindness, which guide an individual's actions to foster relationships [9] and increase life satisfaction [10]. In turn, an increase in life satisfaction can lead to a decrease in materialism [11,12]. Thus, we investigated whether practicing acts of kindness influences a decrease in materialism and external aspirations by enhancing affiliation aspirations and increasing life satisfaction. Our results may contribute to a better understanding of the relationship between kindness and materialistic attitudes and consumption behaviors. This study is of grea<sup>t</sup> practical importance, as a researchers should focus on developing evidence-based measures to reduce materialistic attitudes, which may yield many personal, social, and health benefits [1] and can improve public health [7].

**Citation:** Dr ˛azkowski, D.; ˙ Trepanowski, R. A Longitudinal Experimental Study Examining How and Whether Practicing Acts of Kindness Affects Materialism. *IJERPH* **2022**, *19*, 16339. https://doi.org/10.3390/ ijerph192316339

Academic Editors: V. K. Kumar and Jasmin Tahmaseb-McConatha

Received: 15 October 2022 Accepted: 2 December 2022 Published: 6 December 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### *1.1. Materialism and Well-Being*

Richins and Dawson [13] highlighted three main dimensions of materialism: (1) material possessions as a definition of success, (2) material possessions as a source of happiness, and (3) the centrality of material possessions in one's life. Materialism is expressed, among other ways, in a higher frequency of impulsive purchases; that is, purchases made according to a powerful urge to make them immediately without careful consideration of the consequences [14,15].

A comprehensive meta-analysis by Dittmar et al. [3] demonstrated a clear, consistent negative association between materialism and personal well-being that was stable across different operationalizations of the construct and different personal and cultural characteristics. On average, materialists, compared to non-materialists, are less satisfied with their lives, relationships, friendships, and living standards [1,2,4,13,16,17]. Materialists, compared to non-materialists, are more depressed [18], feel less meaning in life [19], and experience greater anxiety [20]. Since high materialism may impair mental health and the social functioning of individuals, which are important in the perspective of public health, it can be perceived as a public health threat [7,21,22].

One theory that explains why materialists are less happy in comparison to nonmaterialists is SDT [23]. This broad theoretical framework systematically explains human motivation, needs, and well-being dynamics. SDT distinguishes between two basic types of motivation: intrinsic (the inherent tendency to seek out novelty, challenges, enjoyment, and the extension and exercise of one's capacities) and extrinsic (the performance of an activity for reasons other than inherent satisfaction). Kasser and Ryan [18,24] assumed that SDT links these two types of motivation with different aspiration types. According to them, internal aspirations are personal development, self-acceptance (a sense of competence and autonomy), relationships with others (satisfying relationships with family and friends), communality (the desire to actively and productively work for the global good), and health (the absence of illness or any health complaints). External aspirations include wealth (financial success and possession of material goods), fame or popularity (being famous, recognized, and admired), and attractiveness (fashionable clothes, an appealing face, and an attractive physique). The pursuit of external aspirations is closely linked to the possession of materialistic attitudes and values [19].

A person focused on external aspirations pursues activities related to earning rewards and being appreciated by others. In contrast, a person focused on intrinsic aspirations pursues activities that align with universal psychological needs, which provide satisfaction and lead to a greater sense of happiness than a focus on external aspirations. Past research has confirmed these assumptions by showing that people who predominantly adhere to extrinsic aspirations (relative to intrinsic aspirations) have a lower level of well-being [8,17,19,25]. Individuals who acquire material possessions to become happy are less concentrated on performing activities to achieve internal aspirations, and as a result, they experience a lower level of well-being [18,24]. Longitudinal studies have shown that people's well-being deteriorates as they place relatively more importance on materialistic, external aspirations and values [1]. Based on this reasoning, it can be expected that encouraging individuals to be more intrinsic aspiration–oriented will increase their happiness and make them less external aspiration–oriented, which is associated with a reduction in materialism.

#### *1.2. Kindness, Materialism, and Life Satisfaction*

Kindness refers to actions intended to benefit others [26,27]. No other study has directly examined the relationship between kindness and materialism. However, the relationships between materialism and constructs opposite to kindness, such as selfishness, are well documented [13,17]. For instance, previous research has found that materialists are less likely to be charitable and generous and to perform volunteer work [13,16,17]. In general, materialism harms relationships [17] and reduces cooperation [28].

Furthermore, materialism causes the erosion of friendships and prosocial behaviors by fostering the viewpoint that people, like items, exist for the benefit of others. Perhaps concentrating on material goods makes high materialists less open to the needs and problems of other people. Thus, it could be expected that kindness and materialism are negatively related. The above analysis indicates that there may be direct links between kindness and materialism, but mediating mechanisms can also be expected.

First, both kindness and materialism show relationships to life satisfaction. A recent systematic review and meta-analysis demonstrated that performing acts of kindness significantly improves well-being [10]. Performing daily acts of kindness can increase life satisfaction [29]. Different types of kindness can lead to increased well-being, e.g., being kind to others, being kind to yourself or actively observing the kindness happening around us [30]. Acts of kindness are likely to contribute to well-being when they are varied (not repeated) [31] and when they are autonomous (not forced) [32,33]. Performing acts of kindness can lead to an increase in well-being by satisfying the fundamental psychological needs from the SDT: autonomy, competence, and relatedness [34]. Evolutionary psychology, in addition, explains the relationship between kindness and life satisfaction [10] by positing that actions focused on survival and reproduction will produce an intrinsic reward in the form of increased happiness [30]. Several evolutionary theories explain why being kind, as expressed in helping others, can increase the chances of survival and reproduction [35]. Hence, evolution "rewards" kind individuals with an increase in happiness, to increase their chances of survival and reproduction. Thus, kindness may be at least partially genetically determined and innate [10]. These evolutionary roots of kindness have become the basis for diverse cultural norms that promote kindness between different peoples [36]. Therefore, kindness also depends on the culture and the historical time in which the individual lives. Regardless of the evolutionary and cultural determinants of kindness, research results on the intentional and conscious practice of acts of kindness shows that individuals can influence their own development of kindness [10].

Practicing acts of kindness, as described above, leads to an increase in life satisfaction. In addition, as other studies have shown, an increase in life satisfaction, e.g., through practicing gratitude (which arises when individuals receive acts of kindness from others) [26], can decrease materialism [11,12]. Thus, practicing kindness can increase life satisfaction, leading to a decrease in materialism. This leads to the following hypothesis:

**H1:** *Performing acts of kindness (vs. control activity) increases life satisfaction (H1a) and decreases materialism (H1b), external aspirations (H1c), and the intention to buy impulsively (H1d).*

#### **H2:** *Performing acts of kindness (vs. control activity) increases life satisfaction, which in turn decreases materialism (H2a), external aspirations (H2b), and the intention to buy impulsively (H2c).*

Second, SDT offers an alternative explanation for the effect of kindness on materialism. According to SDT [8,18,24], kindness can be considered as strongly related to intrinsic aspirations, especially affiliation aspirations. As previous research has shown, kindness may protect against the degradation of close social bonds, as it relates to feeling connected with other people [37] and can foster relationships [9]. Assuming that an increase in focus on internal aspirations decreases focus on external aspirations, practicing acts of kindness through an increased focus on affiliative aspirations can be expected to contribute to a reduction in emphasis on external aspirations, which will be associated with a decline in materialism. Building on the above reasoning, the following hypothesis is offered:

#### **H3:** *Performing acts of kindness (vs. control activity) increases affiliation aspirations.*

**H4:** *Performing acts of kindness (vs. control activity) increases affiliation aspirations, which in turn decreases materialism (H4a), external aspirations (H4b), and the intention to buy impulsively (H4c).*

#### *1.3. The Current Study*

The primary objective of our research was to explore the links between kindness and materialism. More specifically, we examined whether practicing acts of kindness decreases materialism, external aspirations, and the intention to buy impulsively. We expected

these relationships to be mediated by increased life satisfaction and a focus on affiliation aspirations. Thus we applied a mediation approach, which allowed us to understand the psychological processes through which the independent variable (i.e., practicing acts of kindness) affects dependent variables (i.e., materialism, external aspirations, and the intention to buy impulsively) [38]. As we have described, the theoretical basis for the relationship between practicing acts of kindness and life satisfaction, as well as life satisfaction and materialism, can predict the presence of an indirect effect. We employed a method of the practice of acts of kindness developed within the paradigm of positive interventions, whose effectiveness in enhancing life satisfaction has been confirmed in previous studies [10]. Using the positive intervention paradigm, it is possible to apply the practice of kindness to reduce materialism in everyday life. To verify our hypotheses, we designed an experimental study with two conditions: an experimental (practicing acts of kindness) and a control (practicing neutral activity) condition. We assessed levels of materialism, life satisfaction, and intrinsic and extrinsic aspirations before and after the experimental manipulation. However, we measured kindness only at the pretest to ensure that there were no differences in its level between the intervention and control conditions. In addition, we used a vignette to measure the propensity to make an impulsive, unnecessary purchase in the post-test only.

#### **2. Materials and Methods**

#### *2.1. Participants and Procedure*

We conducted a longitudinal intervention study. As the study was conducted in a social sciences faculty with a low percentage of male students, it was decided to include only females. In this way, a non-proportional sex distribution among participants was avoided at the cost of limiting the representativeness of the results to only females. In the pretest, 156 female students aged 18–39 ( *M* = 20.95, *SD* = 2.70) participated. All participants had completed secondary education and were in the process of acquiring higher education credentials. Of the participants, 122 (79%) remained in the study and participated in the post-test. To recruit prospective participants, we sent study invitations to the firstand second-year female students of the Faculty of Social Science at Adam Mickiewicz University in Poznan, Poland. The data are freely available in the Open Science Framework: https://osf.io/bc67z/?view\_only=bf4933a3537c4fb3be29baec43a5b761, accessed on 6 October 2020. All procedures performed in the study followed the ethical standards of the Ethical Committee of the Faculty of Psychology and Cognitive Science, Adam Mickiewicz University in Pozna ´n. All participants provided written informed consent. Participants were informed that the study aimed to investigate the factors influencing the effectiveness of exercises in increasing happiness. The participants who finished the study received a cinema voucher as promised. The voucher was used as an incentive to participate in the study.

There were six steps to the study: (1) pretest + first intervention (counting acts of kindness), (2–5) interventions (practicing and counting acts of kindness), and (6) posttest. The pretest was carried out during lectures at the university. After the pretest and before the first intervention, participants were randomly assigned to either the kindness intervention or active-placebo control activities and were emailed a link to a dedicated website with further instructions. The instructions for each condition that the participants were presented with are available in the supplementary file.

The participants received a message every three days inviting them to participate in the next step of the study. The participants were asked to complete the intervention (perform up to five acts of kindness or perform up to five activities related to studying) on the day they received the message or the day after. As a result, we collected data from most of the participants' activities in both conditions every 3–4 days. Reminders prompting the completion of the exercises were sent the day after the beginning of each step. On average, it took 21 days to complete the intervention. Verifications of whether interventions were implemented were made by analyzing the content of activities described in both conditions

on a dedicated website. After omitting two interventions, participants were removed from the study. At the end of the study, all participants were debriefed.

To increase the effectiveness of the kindness intervention, the participants were encouraged to perform a diverse range of acts of kindness and, along with a link to each subsequent step of the study, support messages from fictional participants of previous studies were sent. This method for enhancing the intervention and the created messages were based on the research of Nelson et al. [32], where the authors developed a six-weeklong intervention. Performing acts of kindness has been shown to increase happiness in participants in interventions lasting from one day [39] to 10 weeks [40]. In general, positive interventions are more effective if they last longer [41,42]. Because the recruitment process of the study participants (students) was stretched over several weeks, we were able to design a 3-week intervention so that the last recruited participant completed participation in the study before the start of the examination session. At each step, we provided the participants with a different message, for example:

Kindness condition: Hey! You can study anywhere and anytime! You'll surely have plenty of opportunities!

Control condition: Hey! You can do acts of kindness anywhere and anytime! You'll surely have plenty of opportunities!
