Festinger (1954) proposed that human social behavior stems from the drive for self-evaluation and the need for such evaluation with others, which is innate and varies in the absence of a clear ranking of relevant behavioral standards. When individuals are in a low-certainty environment, they gain a sense of control by comparing themselves with others in the absence of objective criteria or perceived irrelevance. Social comparison involves a series of social and cognitive activities. People evaluate, improve, or enhance themselves by comparing their thoughts, feelings, and behaviors with those of others (Stapel and Koomen, 2001) and influence individuals’ social behaviors or emotions. The results of such influence are related to the direction of social comparison. In a related study on classroom behavior, researchers found that students prefer to compare their performance upwards, especially those who perform better than themselves but are like themselves in terms of related or unrelated attributes. This upward comparison affects students’ academic performance and self-concept (Dijkstra et al., 2008).

A related study on cancer patients showed that cancer patients with low self-esteem and a low ability to control their symptoms and disease may have a negative reaction to both downward and upward social comparisons (Buunk et al., 2007). Studies suggest that social comparison has a significant effect on altruism, which is related to the direction of comparison. Compared to upward social comparison, DSC has more positive effects on prosocial behavior (Ye et al., 2021). Through experiments, Klein (2003) found that feedback, especially comparative feedback, affects the degree to which recipients are willing to help others. Participants who received positive feedback on the task were more likely to provide useful hints to another participant on a follow-up task than those who received negative feedback, particularly in situations in which feedback was provided to other participants or the average person. Schlosser and Levy (2016) also found that people who make downward comparisons are more likely to view donations as a way to express altruistic values and are more willing to give donations than those who make upward comparisons. Based on this discussion, we propose the following hypothesis.

The concept of a just world was first proposed by Lerner (1965); individuals believe that the world in which they live is stable, orderly, and just, in which everyone will receive fair treatment, enjoy their employment rights, and reap what they have sown. BJW is a basic need for individuals, helping them rebuild their sense of fairness, enhancing their sense of control, reducing anxiety, and positively impacting their adaptive function (Lerner and Miller, 1978). BJW is generally divided into two fields: PBJW and GBJW. PBJW refers to the belief that individuals deem that they are treated as fairly as they deserve, while GBJW refers to the belief that individuals deem the world fair and that everyone is treated as they deserve (Dalbert, 1999).

According to attribution theory, socioeconomic status is closely related to people’s BJW, and those with higher socioeconomic status are more likely to support BJW; they must view the world fairly in order to believe that they have achieved success on their own. On the contrary, people with lower socio-economic status are less likely to support BJW, maintaining their self-esteem by blaming society rather than their own reasons. In this process, the essence of how wealthy people view the world is a downward comparison regarding wealth, which also leads to and enhances their BJW (Kehl, 2010). Previous studies have further proven this theory (Smith and Green, 1984; Smith, 1985).

The BJW has a positive social significance; the more individuals believe that the world is just, the more willing they are to engage in prosocial behaviors (Guo et al., 2022). BJW directly promotes altruism by increasing willingness to help others (Bierhoff et al., 1991). It promotes altruism through indirect variables. Individuals are happy to engage in acts of charitable giving in the community only if they are confident that their cooperative and caring attitude of kindness will not be taken advantage of Guo et al. (2022).

The GBJW and PBJW often function independently. Research shows that PBJW can be reliably distinguished from GBJW as it can independently and positively predict subjective well-being and self-esteem, and this positive effect is not affected by GBJW or good self-perception (Dalbert, 1999). Moreover, PBJW is positively correlated with job and psychological satisfaction (Otto et al., 2009). Compared with PBJW, the expression of GBJW is more sensitive to contextual changes (Alves et al., 2018). For example, in the context of collectivist cultures, GBJW is more recognized and independently predicts the mental resilience of the three samples (Wu et al., 2011). GBJW has also been found to protect the mental health of individuals facing major social disasters. High levels of GBJW can help individuals reduce negative emotions and increase positive emotions (Wang J. et al., 2021).

BJW involves the perception and understanding of the social environment. Different social comparison directions influence the effects of BJW. Bégue (2005) measured the self-esteem of participants in upward or downward comparison social situations and found that when faced with DSC, a high PBJW can help individuals maintain self-esteem under high self-efficacy. In a study related to relative deprivation, Pan and Zhao (2023) demonstrated that upward social comparison weakens PBJW, resulting in them not believing in future promises and adopting more short-sighted immediate reward strategies. In conclusion, DSC may have a more positive effect on BJW. Therefore, we propose the following hypotheses:

The GLS is an important component of subjective well-being and refers to a person’s overall assessment of his or her quality of life according to selected criteria (Shin and Johnson, 1978). GLS is a key factor that affects an individual’s mental health and social relationships. Fuller-Iglesias (2015) found that the higher the satisfaction with social support, the lower the pressure and fewer the depressive symptoms. Longstreet and Brooks’s (2017) study shows that GLS has a significant impact on generalized network addiction and social media addiction, when GLS, Internet addiction, and specific social media addiction are reduced. Bozoglan et al. (2013) found that GLS was significantly associated with self-esteem, loneliness, and Internet addiction. Moreover, it indirectly affects internet addiction through self-esteem and loneliness. Similar findings have been made in studies related to altruism: Ummet et al. (2015) found that the GLS level of college students can predict altruistic behavior, and with the improvement of GLS, their helping behavior toward others will also increase. Valentine et al. (2011) found that when employees have a high degree of career satisfaction, a company’s commitment to positive corporate ethical values significantly improves the degree to which employees help their colleagues.

Generally, life satisfaction involves cognitive judgment and life evaluation. Individuals’ GLS is affected only by what they see in others if they have a strong tendency to compare themselves with others (Buunk et al., 2007). Social comparisons, especially downward comparisons, are better predictors of GLS than factors such as expectations or comparisons with previous situations. In relevant studies on the elderly population, social comparison is a positive adaptive strategy used by the elderly to maintain their GLS (Frieswijk et al., 2004a). Intragroup social comparison has also been found to be a determinant of GLS across racial and ethnic groups (Davis and Wu, 2014). Studies of college students have also shown that social comparison affects students’ evaluations of their friendships, the quality of their social relationships, and their social lives (Buunk et al., 2007). Upward comparisons may reduce GLS (Antinyan, 2016), whereas downward comparisons may enhance it (Frieswijk et al., 2004b). Based on this, this study proposes the following hypothesis:

Regarding the relationship between BJW and GLS, research has shown that BJW is based on people’s belief that the world is just and that they can obtain what they deserve, which is a crucial factor affecting GLS. When BJW increases, GLS tends to increase (Tian, 2019), whereas a decrease in BJW decreases GLS (Chen et al., 2022). Hirshleifer (1987) believed that empathy was the driving factor in maintaining social fairness and justice. Individuals evaluate situations and clarify empathy through social comparisons with others (Buunk et al., 1990). The empathy generated during the comparison process also influence the subsequent behavior of an individual (Rotteveel and Phaf, 2007), which is supported by empirical research. Yu et al.’s (2018) study of 372 Chinese college students showed that BJW could significantly predict subjective well-being. Oishi et al. (2011) proposed that perceived inequity mediates the relationship between income inequality and GLS. Income inequality leads to high social comparison, and high social comparison levels lead to perceived inequity and a lack of trust, resulting in low GLS (Figure 1). Accordingly, we propose the following hypothesis:

Convenience samples of 1,764 university students were chosen in this study, including 739 males and 1,025 females from one college in Henan province, China. We distributed 1,900 Sojump online questionnaires and 1,850 responses, including data from two time points, were collected, resulting in an impressive 97.4% response rate. After carefully examining the survey data, 86 responses were excluded due to patent responses or excessive missing values. Consequently, the final analysis included a total of 1,764 valid responses. The inclusion criteria for our sample were students enrolled in this college, while the exclusion criteria included incomplete questionnaire responses or evident response patterns indicating non-serious participation. Participants were selected based on their willingness and ability to provide consistent responses over time. The average age (M_age) was 19.21 years, accompanied by a standard deviation (SD_age) of 1.00 years with the majority falling into the age groups of 18, 19, or 20 years, comprising 22.0, 40.0, and 25.7% of the sample, respectively. Notably, the highest proportion of participants, 40.0%, fell into the 19-year-old group, highlighting the significance of this age cohort in the study. We collected the data from two time points with an interval of 2 months. The study was conducted in 2022, collaborating with local education bureaus and ensuring voluntary participation.

Descriptive statistics and correlation analyses were performed using SPSS26.0, while Mplus 8.3 was used to analyze the multi-mediating effects.

This study showed that DSC positively predicted college students’ altruism, which was consistent with H1. This suggests that college students who scored higher on the downward social comparison variable are more likely to engage in altruistic behavior. Warneken (2009) argued that social factors are important variables that influence altruistic behavior. As individuals grow older, they selectively choose to understand and experience altruistic behaviors based on their social cognition. This argument is supported by the results of this study, in which DSC was a significant positive predictor of altruism. This study is also consistent with existing research showing that DSC promotes individuals’ tendencies to be generous (Ye et al., 2021) and sympathetic toward those they are comparing themselves to, thereby exhibiting more apparent altruistic attitudes and behaviors (Batson, 1991). According to the empathy-altruism hypothesis, empathy has significant positive correlation with altruistic behavior, and the sympathy and compassion generated by empathy promote altruism (Baston, 2010). Based on the contrast-empathy model, we found that when compared to those who are less fortunate, people’s feelings of pity and empathy are awakened. However, other scholars believe that in the process of downward comparison, individuals, especially college students with strong self-awareness, tend to feel their worth and will enhance themselves by further empathizing with others or helping them, which will manifest as altruism in the outside world (Song et al., 2019).

The mediating effect indicates that an independent variable on a dependent variable is transmitted through a third variable, which is called a mediator (VanderWeele and Vansteelandt, 2014). Our study found that BJW has a mediating effect between DSC and altruism. In other words, apart from direct effects, DSC also affects altruism through GBJW and PBJW (indirect effects). The social comparison theory states that people tend to compare themselves with others. This comparison impacts individual psychology and behavior, depending on the direction of the upward or downward comparison. Many studies believe that upward comparison has a negative impact on individuals (Wang et al., 2020) whereas downward comparison has a positive impact (Vrugt, 1994). This study confirms that this result also applies to the effects of social comparison on BJW. DSC can significantly and positively predict GBJW/PBJW and increases with an increase in DSC scores. By comparing downwards, individuals will gain a stronger sense of both GBJW and PBJW. This may explain why BJW is closely related to individuals’ social status. In DSC, individuals have a relative competitive advantage compared to individuals of a lower status or disadvantage, thus enhancing their BJW. In situations where individuals compare themselves to others with lower status or disadvantages, they may feel a sense of relative superiority and believe that they have earned their status through their efforts and deservingness, thus enhancing their BJW (Wang H. X. et al., 2021).

This study also found that PBJW could significantly and positively predict altruism, which indicates that college students with higher scores on PBJW are more likely to engage in altruistic behavior. BJW can enhance an individual’s sense of stability and control over the environment and promote the formation of altruism through the mediating role of gratitude and self-esteem (Jiang et al., 2017). In contrast to previous studies on collectivist cultures, in this study, PBJW showed a stronger mediating effect than GBJW. This may be related to the relationship between social comparison and altruism, which is the focus of this study. Bégue (2005) pointed out that PBJW plays a crucial role in helping individuals maintain their self-esteem when facing unfavorable social comparisons. Correia et al. (2016) showed that PBJW was significantly correlated with helping others, whereas GBJW was not. This may be due to the phenomenon of selfish bias in fair inference, referring to the tendency of individuals to perceive themselves as being more deserving of positive outcomes than others (Donat et al., 2018). This is possibly because the world itself is unjust, and there is a gap between the PBJW and GBJW. Some people are more likely to obtain justice than others (Thomas and Rodrigues, 2020). Therefore, we must acknowledge that when facing others less fortunate, people may not be motivated by their own desire to make the world fairer to everyone and bring happiness. However, their improved PBJW may encourage them to engage in altruistic behavior and demonstrate their superiority over those who are not as good as them.

The results show that GLS has a significant mediating effect on DSC and altruism. This suggests that individuals who prefer to make DSCs are more likely to achieve higher general satisfaction, which can prompt them to engage in altruistic behavior. Downward comparison provides a low reference point for people to evaluate themselves, which helps them define their situation more positively, thereby improving their GLS (Buunk et al., 2001). Self-enhancement is one motive for DSC. In the process of downward comparison, individuals feel their value, their GLS improves, and they tend to further enhance themselves by empathizing with or helping others, which manifests as altruism in the outside world (Song et al., 2019). Therefore, when an altruistic situation exists, such as donating or volunteering, people can make downward comparisons. Moreover, when people seize this opportunity to compare their lives with assistance, they feel higher GLS, which motivates them to engage in altruistic behaviors (Huang, 2016).

Multi-mediating effect refers to multiple mediation with more than one intermediate mediator that has a series of indirect effects of dependent variables on independent variables (Robins and Greenland, 1992). Our results found that in the path of DSC affecting altruism, BJW and GLS showed a significant multi- mediating effect in the relationship between DSC and altruism; that is, DSC affected altruism by affecting BJW and GLS. DSC is more likely to maintain PBJW. It consists of the social comparison theory, in which unique patterns of cooperation among humans are based on the fairness of social comparison. People often prefer fairness and seek to reduce the unfairness between those who are superficially similar to them (Gheorghiu et al., 2021). Thus, individuals’ BJW affects their GLS (Tian, 2019) and behavioral patterns (Herrmann et al., 2019). When individuals feel that others are treated unfairly, BJW will make them think that they are favored by the world (Correia et al., 2016). When individuals obtain what they deserve, their GLS increases (Correia et al., 2009), and they are expected to maintain their inner BJW by helping others (Igou et al., 2021), showing their altruistic attitude and behavior (Duncanson, 2007; Gheorghiu et al., 2021). Based on the results of this study, during educational practice, intervention in social comparison among college students can enhance their perceived BJW, thereby improving their general life satisfaction and encouraging them to engage in more altruistic behaviors.

Though the current study has found some interesting things, it is still open for challenge or improvement because of some limitations. First, this study only considers the impact of downward comparison on altruism, while Li et al. (2021) suggested that downward comparison may not always bring positive effects, and the different mechanisms of downward comparison and downward identification should be considered. Similarly, the addition of upward comparisons, including upward contrast and upward identification, will enrich research results. Second, this study considered the causal relationship between downward comparison and altruism; however, the research subject was limited to college students. Future studies should increase the sample contrast between middle school and college students to reveal the dynamic relationship between downward comparisons and altruism more clearly. Finally, this study only discussed the influence of individual factors on altruism, which could increase the perspectives of society and family in the future, leading to a more comprehensive understanding of the development of altruism.