Background
Social decision-making, including a variety of phenomena such as reciprocity, cooperation, fairness perceptions and fairness judgment, refers to decision-making behavior in the context of social interaction [
30,
36]. For humans living in a complex social environment, it is during social interaction that many crucial decisions are made [
8]. Adolescence is a developmental period characterized by dramatic changes in both physiology and psychology, and it is a time when individuals are engaged in more social communication and faced with more social decisions [
51,
78]. For instance, Zhang, Xu and Ding [
79] demonstrated that the cooperative behavior of adolescents appeared to decline with increase in age. Although adolescents could perform similarly to adults in cognitive decision abilities [
53], the unique characteristics of the social decision-making of adolescents are determined by their emotional sensitivity, instability, and poor self-control [
4]. Therefore, exploring the characteristics, and capturing the rules of social decision-making in adolescents could serve to improve their social decision-making ability and promote scientific psychosocial education.
The Ultimatum Game (UG) is a standard paradigm used to explore social decision-making, in which the behavioral response of participants toward different levels of unfairness can be investigated by simulating the allocation of funds in social interaction [
31,
37]. Typical UG involves a “Proposer” and a “Responder”, and a certain sum of money is shared by both at the beginning of each round. The proposer then proposes a share of this money to the responder, who can either accept or reject this proposal. If the responder accepts the proposal, money is shared in proportion to the proposal; however, if the responder refuses, both players gain nothing in that round. According to the principle of benefit maximization in game theory, responders should accept any nonzero proposals; rejecting an unfair proposal would be considered irrational from this economic perspective [
11]. Nevertheless, studies indicate that unfair proposals are often rejected [
14,
75,
81]. Thus, there are two potential outcomes of decision-making for responders—to accept or to refuse. While making decisions, the responder must judge the acceptability of the proposal according to her or his own fairness standards [
44]. Therefore, indicators such as the acceptance rate of proposals and fairness perceptions are usually used to investigate the decision mode of the responder [
32,
82].
Adolescents experience dramatic changes in both physiology and psychology [
51,
78]. As a result, social decision-making in adolescents has attracted the attention of researchers [
49]. This is a vulnerable period when the occurrence rate of depression increases dramatically [
48], with the detection rate of depression ranging from 20 to 44% [
26]. Depression and decision-making are closely connected [
21]. Relative to healthy people, those with depression perform somewhat maladaptively in terms of fairness, cooperation, altruism and other social principles (e.g., decrease in cooperation, excessive altruism). As such, the acceptance rate of unfair allocation appears to be higher in individuals with depression, suggesting that they attempt to maintain “group fairness” at the expense of self-interest. However, Scheele et al. [
55] suggested that individuals with depression are more likely to reject unfair proposals and tend to regard others’ proposals as unfair ones. The inconsistent conclusions reported by studies of decision-making in individuals with depression may be due to the different levels of depression they are experiencing [
68] or the consumption of different psychotropic drugs [
19]. Indeed, the significant relationship between pubertal transition and depressive mood that does not meet the diagnostic criteria for depression has also been emphasized in several studies [
27,
28,
38]. Specifically, depressive mood was found to increase linearly for 10–19 year-olds, presenting as a persistent symptom of dispiritedness [
66]. This raises the question of whether adolescents with depressive mood show differences in social decision-making from their normal mood peers. Based on the available evidence, we propose that adolescents with depressive mood may manifest higher acceptance rates of unfair allocation than their healthy counterparts, while their fairness perceptions may be lower. These proposals are formalized in terms of the following hypotheses.
A prominent change in adolescents’ evaluation of fairness, trust and reciprocity might alter their considerations of fairness, which would then have an effect on their social decision-making [
16]. In line with fairness theory, individuals consider whether their costs and benefits are basically the same in comparison with others; hence, responders care not only about their own benefit but also about proposers’ relative gains. This suggests that different perceptions of fairness for different allocation proportions may lead to different social decision-making behaviors.
Allocation proposals were categorized inconsistently in previous studies using UG. According to the proportion that responders and proposers gained, proposals could be categorized into two levels. For example, Wu and Zhou [
70] categorized proposals into fair (5:5, 4:6) and unfair (2:8, 1:9) levels; Destoop et al. [
19] categorized proposals into fair (5:5) and unfair (3:7, 2:8 and 1:9) levels; and Gradin et al. [
29] categorized proposals into fair (38–50%) and unfair (8–33%) levels according to the percentage of the total money that responders gained. Meanwhile, some researchers set three levels of proposals. For example, Huang et al. [
39] categorized proposals into fair (5: 5), generous (9:1, 8:2) and selfish (1:9, 2: 8) levels; Wang et al. [
68] categorized proposals into fair (50–40%), unfair (33–25%) and extremely unfair (20–10%) levels. Other researchers have set five levels of proposals according to the specific amount of money [
64,
83]. As we can see, most of the studies set two, three or five levels of allocation proposals based on the levels of fairness. However, it is too complicated to compare experiments using previous sets because of the one-to-many relationship, which means that there are multiple allocations in one level. Thus, in the current study, to better explore the effect of fairness perception differences caused by different proposals on the social decision-making of adolescents, the allocation proposals were categorized into three levels (fair (5:5), unfair (3:7) and extremely unfair (1:9)), which would not only simplify the proposers’ choices and the experiments, but also increase the representativeness of the proposals for different levels of fairness. Hypothesis 2 was posited based on this notion:
Decision-making is more likely to be influenced by social comparison in the context of social interaction [
54]. Festinger [
24] proposed that, following typical social comparison theory, individuals could not help but make comparisons with others to learn about themselves, and the results of such comparisons could have an effect on their own decision-making behavior. For adolescents studying in a collective environment and interacting with peers frequently, their behavior and decision-making would be particularly affected by social comparison [
43]. Social comparison is concerned with the processes involved in comparing the position and status (including ability, social status, behavioral pattern) of oneself with others [
58,
72]. However, it is the tendency toward social comparison [
41,
81], in particular, its frequency, that came to the attention of researchers, with less attention given to the different ways in which comparisons are made. From the perspective of social comparison, there are three types: lateral comparison, downward comparison and upward comparison. Lateral comparison is comparing oneself with those who are similar, while downward and upward comparison refer to comparing oneself with those who are, respectively, weaker in some respects, or better off. The different types of social comparison certainly have an impact on individuals’ social decision-making [
62,
74]. Specifically, Brickman et al. [
7] demonstrated that upward comparison might hurt an individual’s self-esteem and make her or him perceive threats and experience negative emotions elicited by this comparison, which may lead to a higher rate of rejection toward unfair allocation proposals. Additionally, it was found that individuals’ self-esteem and happiness could be raised by downward comparison, which may also moderate their negative emotions when facing unfair allocations and thereby increase their rate of acceptance [
69]. Given the strength of the evidence, it is certain that the type of social comparison has a noteworthy impact on social decision-making. Despite previous studies focused on one aspect of social comparison, little is known about the effect of social comparison on social decision-making. Therefore, we intended to comprehensively explore the effect of upwards and downwards social comparison on social decision-making. Hypothesis 3 was proposed with this aim in mind:
In light of their development of cognitive ability and increase in social communication, adolescents may make more social decisions that are significantly affected by social comparison, depressive mood and levels of fairness of proposals. Studies have shown that social comparison is related to depression and further indicated that depressive individuals compare themselves with others more frequently and use more upward comparisons [
1]. Additionally, social comparison is also under the effect of fairness level in UG; that is, unfair proposals could trigger more downwards comparisons to allow individuals to maintain a position of relatively higher self-esteem [
46].
Thus, we reasoned that the effect of social comparison, depressive mood, and levels of fairness of proposals on social decision-making would be interactive and complex, rather than completely independent.
-
H4: The interaction of fairness level, social comparison and depressive mood is significant in the process of social decision-making among adolescents. Fairness level, social comparison, and depressive mood have a common effect on the social decision-making of adolescents.
Social decision-making usually contains two situations—gain or loss—with individuals valuing the trade-off of loss more than gain [
32]. The framing effect on social preferences proposes that individuals are influenced by the framework of optional proposals when making decisions, which then alters their tendency toward cooperation, reciprocity and altruism [
18]. Previous studies using UG have revealed that, for responders, comparing their profits to that of proposers could influence their perceptions of fairness in the situation of gain, whereas the impact of loss on their perceptions of fairness remains unclear [
44]. With a typical UG, there is no difference between decisions in the gain situation, whereas the proposer and the responder both share the loss in the loss situation. If the proposal is accepted, the money is divided between both players according to the proposal (i.e., they experience the gain together according to the proportion in the proposal). By contrast, both players split the loss of the total amount if the proposal is rejected. It was found that individuals show lower fairness perceptions and a higher rejection rate of unfair proposals in the condition of loss [
32]. However, Li et al. [
44] demonstrated that the acceptance rate is higher in loss situations than in gain situations. In summary, studies of social decision-making in different contexts have not reached a consensus, suggesting that further clarification is required. Accordingly, in the following experiments we explore the social decision-making of adolescents in gain and loss situations.
Taken together, starting with multiple variables and using the UG, we examine the effect and interaction mechanism of fairness level, social comparison and depressive mood on the social decision-making of adolescents in different situations. First, experiment 1 examines the effect of depressive mood and social comparison on the social decision-making of adolescents in gain situations. Subsequently, experiment 2 explores the effect of depressive mood and social comparison on the social decision-making of adolescents in a loss situation.
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