Gender differences in guilt aversion in Korea and the United Kingdom

Guilt aversion, which describes the tendency to reduce the discrepancy between a partner’s expectation and his/her actual outcome, is a key driving force for cooperation in both the East and West. A recent study based on functional magnetic resonance imaging and online behavioral experiments reported that men show stronger guilt aversion than women and also suggested that men’s predominance in guilt aversion arises from stronger sensitivity to social norms. However, since the participants of that study were all Japanese, it remains unaddressed how common the gender difference in guilt aversion is. Here, we conducted online behavioral studies on people from Korea and the UK (Korea; n = 294, UK; n = 347) using the same trust game. We confirmed that men exhibit stronger guilt aversion than women in both countries. Furthermore, consistent with the Japanese study, our Lasso regression analysis for UK participants revealed that Big Five Conscientiousness (rule-based decision) correlated with guilt aversion in men. In contrast, guilt aversion in Korean men correlated with Big Five Neuroticism. Thus, our results suggest that gender differences in guilt aversion are universal but the underlying cognitive processes may be influenced by cultural differences.

. Descriptive statistics for the online sample Table S2. GLM regression of gender differences for guilt Table S3.GLM regression of gender differences for the cognitive strategy of guilt aversion Table S4. Lasso regression of gender differences for inequity Instructions Personality questionnaire

Behavioral results of the gender differences for inequity.
For the inequity-aversion behavioral analysis, we replaced the target variable ( ) and performed the same Lasso regression as the one for guilt aversion (see Supplementary Fig. S2 and Table S4). Supplementary Fig. S2a and Table S4(1) present the Lasso regression results to identify the relationship between inequity aversion ( ( ) ) and gender under a controlled socioeconomic status. We found that gender had no weight in either the Korean or U.K. populations. However, this result is not consistent with previous empirical studies (for a review, see [1]). For the U.K., openness and education had large positive weights. Supplementary Fig. S2b and Table   S4(2) present the Lasso regression results to identify the cognitive mechanisms specific to gender. We found that the interaction term of gender with personality traits had no weight in the Korea or U.K. populations.

Why were there no gender differences for inequity aversion?
Although we found that both countries were inequity averse (see Table 1), we did not observe gender differences in inequity aversion. However, many previous studies have observed differences in inequity aversion, including studies on populations in Korea and the U.K. Those previous studies often used dictator games and social value orientation tasks, which are suitable for focusing on inequity aversion. On the contrary, our trust game was primarily designed to measure guilt aversion. Thus, a potential reason for the inconsistent results is the experimental tasks used. Another potential reason is that the mental concentration of the participants was lower while conducting the task online.
Indeed, the withdrawal rate in the present study was higher than in our previous study [2].
In any case, we believe we can remove the effect of inequity aversion from the analysis of guilt aversion using the present task.    Notes: Standard errors are in parentheses. All coefficients and standard errors are shown multiplied by 10 3 . Significance: * * P < 0.01; * P < 0.05. Notes: Standard errors are in parentheses. All coefficients and standard errors are shown multiplied by 10 3 . Significance: * * P < 0.01; * P < 0.05.  Notes: All scores are Lasso regression coefficients and are shown multiplied by 10 3 .

General introduction
In this experiment, you will be paired with another person. In each pair, one person will be Player A and the other will be Player B. You will be participating in a game, which will be explained later. During this experiment, you will be asked to make a number of decisions, and you will change pairs each time you make a decision so that you are paired with the same person only once. The experiment is strictly anonymous; that is, your identity will not be revealed to others, and others' identities will not be revealed to you.

Rules of the game
Please review and ensure that you understand the rules of the game by referring to the following figure. Every time you make a decision, a figure similar to the one below will be displayed, but the values in the figure will change.
1. In the first stage, Player A will make two decisions based on the amount of money in the game. For the first decision, Player A must choose W or Z. If Player A chooses Z, Players A and B will receive and pence, respectively. If Player A chooses W, then Player B will make the decision.
For the second decision, Player A must report a belief probability from 0% to 100% in increments of 10% that Player B (partner) will choose R.

3.
Procedure of the experiment Here, we will explain the tasks along the flow of the experiment. You will first make one decision as Player A and then make 45 further decisions as Player B.
1. First, a game will be displayed on your screen, and you (as Player A) will choose W or Z and reveal your belief probability that Player B will choose R based on the amount of money in the game. You will experience one trial as Player A. Your choices will be used when Player B makes their choice in the next stage.
In this experiment, many participants will make decisions as Player A, just as you did; therefore, it is uncertain whether the decision you make as Player A will be used in the next stage. If your choice is used in the next stage, you will receive money according to the choices made by both you and your partner. Therefore, if you choose Z in today's experiment and the earnings are already fixed, you will not be paid if it is not used in the experiment. We will contact you again if we have to pay.
2. Next, another game will be displayed on your screen. In this game, you will make