Our study involves 8 Treatments, each with 2 or 3 stages. In all Treatments, participants made a series of decisions in which they chose how to allocate tokens between themselves and a particular anonymous partner. In the first stage, allocators are endowed with ten tokens and are instructed to play a conventional dictator game with a recipient (reciprocator). The allocators reported contributing an average of 3.09 tokens (N = 128, M = 3.09, SD = 1.98, Min = 0, Max = 8), consistent with the literature indicating that dictators allocate 20 percent to 30 percent of the endowment5. The reciprocators then returned the favor by making the same allocation decision without knowing the number that the allocators had given to them. They have allocated a mean of 2.68 tokens. We also asked some reciprocators to estimate the number and gave a bonus for more accurate estimates. Later, we informed the reciprocators of the number of tokens that allocators had initially given to them. In addition, we reminded them of their allocations and estimates. Given the information, reciprocators have the option of adjusting their earlier allocations.
Reciprocity and Motivated Self-serving Beliefs
We searched for evidence that the self-serving bias is motivated by the self-serving beliefs of others' morality (e.g., the belief that others are selfish). We examined this possibility by probing the subjective beliefs of reciprocators regarding the number of tokens allocated to them. As the reciprocators were to reciprocate back the favor, we also manipulated the sequences of estimation and allocation of the reciprocators to see whether the timing of allocations affects estimations or vice versa. In Treatments 2 and 4, the reciprocators estimated before they made allocations, whereas, in Treatment 3, the sequence was inverted.
In addition, we introduced monetary incentives to motivate reciprocators' estimates to be accurate. In Treatments 2I, 3I and 4I, we offered monetary incentives that scaled directly with estimating accuracy. We anticipated that incentives would elicit reciprocators' true beliefs of the allocators. We hypothesized that those reciprocators who think allocators to be fair and generous (i.e., those who estimated the allocators to give them a fair number of tokens) would reciprocate this generosity (i.e., return a fair number of tokens to the allocators). In contrast, those who believe others to be selfish (i.e., those who estimated the allocators to give them nothing or few tokens) would do the same to them (i.e., return nothing or few tokens to the allocators).
To test this hypothesis, we dotted each pair of estimates and allocations for each reciprocator (N = 64). As predicted, despite the outliers, we found a strong, positive, linear correlation between estimates and allocations (see Fig. 1). The linear regression analysis (P < 0.001) also supports this conclusion (see Supplementary Information). This finding supports the idea that when individuals consider others to be giving, they will reciprocate by acting generously towards them.
Result 1 (Reciprocity): Reciprocators allocate more to those allocators they believe would do the same to them, indicating a substantial pattern of reciprocity.
Another main issue we focused on is whether self-interested reciprocators would endorse motivated, self-serving beliefs. We hypothesized that regardless of how the reciprocators genuinely perceive the allocators, they would prefer to distort their moral beliefs of them (i.e., believe that the allocators are more self-interested than they truly are). This belief would justify their selfish behavior, provide a justification for themselves behaving selfishly (e.g., allocate few or nothing), and eventually increase their payoffs. If our hypothesis is correct, the incentivized estimates should be closer to the actual number of tokens distributed and greater than those without incentives. Moreover, the estimates without incentives should be closer to the number returned by the reciprocators.
Across all Treatments, the allocations and the estimations were non-normally distributed (W = 0.84-89, p < 0.001; Shapiro - Wilk test). Thus, we report non-parametric statistics for key comparisons. All reported p-values are two-tailed.
We pooled the allocations of all the allocators (N = 128) across all treatments, as their allocations were not affected by other factors. To test our hypothesis, we compared the un-incentivized estimates of the reciprocators (E) with the actual number of allocations (AA). We found no significant difference between these two groups of data (W = 4230.5, p = 0.95; Mann–Whitney U test). Similarly, we also found no significant difference between the incentivized estimates and the actual number of allocations (W = 4195, p = 0.86; Mann–Whitney U test). Nevertheless, even if the reciprocators show no significant self-serving beliefs on the statistical level, we compared the mean value of these data, which would still partially support the hypothesis of self-serving beliefs (see Fig. 2). The average number of tokens the reciprocators gave (AR) was 2.63 (N = 64; SD = 2.20). The mean value of the reciprocators' un-incentivized estimates (E) is 2.84 tokens (N = 32; SD = 2.07), whereas the mean value of the incentivized estimates is 3.13 tokens (N = 32; SD = 1.74). We can see that the estimates with incentives were more accurate on average and higher than those without incentives. Moreover, the mean estimate without incentives was closer to the number of tokens returned by the reciprocators. These results are in accordance with our hypothesis.
In Treatments 2 and 4, the reciprocators made the estimations first and then the allocations. To rule out the possibility that the order between estimation and allocation could affect the reciprocators' elicited beliefs, in Treatment 3, the reciprocators made the allocation decisions first, followed by estimations. We found no difference in the reciprocators' estimations across Treatments 2, 3, and 4 (W = 258.5, p = 0.83; Mann–Whitney U test), indicating that the order of estimations and allocations has little effect on the reciprocators' beliefs regarding the amount allocated by the allocators.
Result 2 (Self-serving Beliefs): The order between estimation and allocation does not significantly affect the reciprocators' elicited beliefs on the allocated amount by allocators. Reciprocators' estimations are insignificantly lower in un-incentivized treatments than in incentivized treatments, providing weak evidence for self-serving beliefs.
Self-serving Regret
To test whether people regret when they realize their beliefs about others are biased, we allowed reciprocators to reallocate. We predicted that the reciprocators would make different adjustments under different circumstances: compared to the actual number given by the allocators, if the reciprocators had under-estimated, they would either slightly upward their previous allocation or make no adjustments; if they had over-estimated, they would downward their previous allocations without hesitation; if their estimations were accurate, they would either choose not to make adjustments or downward their allocations. Thus, we predicted that the reciprocators who under-estimated the allocated amount were less likely to make an upward adjustment compared to the likelihood of a downward adjustment made by those who over-estimated the allocated amount. In addition, the average range of the upward adjustments should be less than that of the downward adjustments. To test this hypothesis, we examined the direction and the intensity of reciprocators' regret (i.e., discrepancies between each reciprocator's estimations and reallocations). If our hypothesis is correct, then such post-decision regret should tend to be self-serving: there is an asymmetry between upward and downward adjustments.
We divided the reciprocators into an under-estimated group (N = 31), an over-estimated group (N = 21), and an accurate-estimated group (N = 12). Regarding the direction of the adjustments, 61.3 percent made upward adjustments for the under-estimation group. Among over-estimators, 80.9 percent made downward adjustments, which outnumbers the former by more than 33 percent. Even with a precise estimation, 16.7 percent of the reciprocators still chose the downward alternative (see Fig. 3). Regarding the range of adjustments, on average, reciprocators who over-estimated opted to decrease 1.9 tokens compared to their initial allocations. In contrast, those who under-estimated increased 1.41 tokes, and those who estimated accurately decreased 0.33 tokens (see Fig. 4). Such a self-serving pattern aligned with our hypothesis: reciprocators who over-estimated (i.e., thinking too good of others) chose to make downward adjustments without hesitation, while those under-estimated (i.e., thinking too bad of others) tended to make slightly upward adjustments.
Still, there is a possibility that reciprocators regret because of the differences in allocations between them and the allocators in the first two stages, which directly affect their payoffs. We compared the allocation differences and examined how they adjusted in reallocation. Our predictions are similar to the above. Compared to the actual number allocated by the allocators, if the reciprocators had under-allocated, they would either slightly upward their previous allocation or make no adjustments; if they had over-allocated, they would downward their previous allocations; if their allocations are the same, they would either choose not to make adjustments or downward their allocations. We also divided the reciprocators into three groups: the under-allocated group (N = 40), the over-allocated group (N = 25), and the same-allocated group (N = 15). Regarding the direction of the adjustments, as for the under-allocated group, 60 percent made upward adjustments. Among over-allocators, 92 percent made downward adjustments. One-fifth of the reciprocators still chose the downward alternative for the same-allocated group (see Fig. 3). Regarding the range of adjustments, on average, reciprocators who over-allocated decreased 2.24 tokens compared to their initial allocations, while those who under-allocated increased 1.50 tokens, and those who allocated the same as the allocators decreased 0.53 tokens (see Fig. 4).
Result 3 (Self-serving Regret): Reciprocators adjust their allocations more in the over-estimated group than in the under-estimated group and also more in the over-allocated group than in the under-allocated group, in terms of both extensive margin and intensive margin, exhibiting a significant pattern of self-serving regret.