Null Results for the Steal-Framing Effect on Out-Group Aggression

doi:10.21203/rs.3.rs-936427/v1

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Null Results for the Steal-Framing Effect on Out-Group Aggression

https://doi.org/10.21203/rs.3.rs-936427/v1

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published 13 Jan, 2022

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Whether intergroup conflict is a necessary condition for the evolution of human prosociality has been a matter of debate. At the center of the debate is the coevolutionary model of parochial altruism—that human cooperation with in-group members has coevolved with aggression toward out-group members. Studies using the intergroup prisoner’s dilemma–maximizing difference game to test the model have repeatedly shown that people do not exhibit out-group aggression, possibly because of an inappropriate operationalization and framing of out-group aggression. The coevolutionary model predicts out-group aggression when the actor understands that it will lead to the in-group’s benefit. However, in the game, such an aspect of out-group aggression that benefits the in-group is typically not well communicated to participants. Thus, this study tested the hypothesis that out-group aggression in the game would be promoted by a framing that emphasizes that attacking out-group members enhances the in-group’s gain. Results of two laboratory experiments with 176 Japanese university students in total showed that such a framing did not promote out-group aggression and individuals invested more money to cooperate with in-group members only, avoiding the strategy of cooperating with in-group members to harm out-group members. These results do not support the coevolutionary model.

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Null results

steal-framing effect

out-group aggression

evolution

human prosociality

laboratory experiments

coevolutionary model

Intergroup conflict, including the extreme case of war, is ubiquitous in human social life [1–3]. Given the importance of understanding the nature of intergroup conflict, researchers from diverse disciplines, such as sociology, political science, economics, and other social sciences, have conducted studies to unravel its causes or reasons [4–6]. In social psychology, intergroup conflict has been attributed to intergroup bias [7, 8], which is the human tendency to behave altruistically or cooperatively toward members of the group to which they belong (i.e., in-group) and/or competitively or aggressively toward members of the group to which they do not belong (i.e., out-group). Various theories have been proposed as a psychological explanation of it [8, 9–11].

Recent experimental studies in social and evolutionary psychology have revealed that intergroup bias mainly stems from in-group cooperation, and out-group aggression rarely occurs in economic games [12–14]. However, based on an evolutionary perspective [15], the absence of out-group aggression in previous studies may be due to the lack of a critical condition, such as a cue that attacking the out-group would increase the benefit to the in-group. Thus, the current study introduces such a cue to an experimental game paradigm and examines whether out-group aggression emerges.

1.1 Coevolutionary model of intergroup bias

Intergroup bias is present even between arbitrarily created experimental groups (i.e., minimal groups) [16]. Intergroup bias in minimal groups—in which no conflict of interest, negative stereotypes, or face-to-face interactions within or between groups exist—has been consistently observed in student [17] and non-student samples [18] across various cultures [19, 20]. Evolutionary and social psychologists have formed several hypotheses on the evolutionary origin of intergroup bias [21, 22].

One of the evolutionary hypotheses explaining intergroup bias is the coevolution model (CO model) [15, 23, 24]. The CO model holds that humans simultaneously acquire in-group cooperation and out-group aggression. Choi and Bowles [15] used an agent-based simulation and showed that agents who displayed both in-group and out-group aggression thrived, suggesting that in-group and out-group aggression co-evolved. The validity of the CO model has been examined using various datasets, ranging from ethnohistorical and archaeological [25] to experimental [26, 27], although evidence for the model has been mixed [14, 28–30].

A feature of the CO model that distinguishes it from other evolutionary models of intergroup bias [22] is the assertion of the existence of out-group aggression. Previous studies have typically employed the intergroup prisoners’ dilemma–maximizing difference game (IPD–MD) [12] to test the CO model experimentally. In the IPD–MD, players are randomly divided into two groups. They receive a fixed amount of money from the experimenter. They decide how much to keep for themselves and to invest in the two pools: the within-group and the between-group pools. The total amount of money invested in the within-group pool by the members of the group is doubled and divided among in-group members equally. In contrast, the total amount of money invested in the between-group pool is doubled; all in-group members receive an equal split and out-group members lose half the amount of the money (equal to the total invested amount before doubling). In other words, any investment in the between-group pool includes harming out-group members, i.e., out-group aggression. If people are inclined to pursue self-interest, they would keep the entire amount of the initial endowment for themselves. If people are inclined only to cooperate with in-group members, they will invest their money in the within-group and/or between-group pools, without distinguishing between the within- and between-group pools. Meanwhile, if people intend to cooperate with in-group members and harm out-group members, they would invest in the between-group pool that reduces the resource of out-group members.

The CO model predicts that individuals are inclined to invest more in the between-group pool than in the within-group pool in the IPD–MD [31]. Nevertheless, several studies have revealed that individuals, in general, invest more money in the within-group pool than in the between-group pool [12, 32–35]. The same pattern has also been observed in studies in which researchers modified the game to encourage investment in the between-group pools [36–41]. Their findings offer conflicting evidence for the CO model: the empirical evidence does not suggest that individuals simultaneously acquire the tendency for in-group cooperation and out-group aggression.

1.2 Out-group aggression in the IPD–MD

Behavioral evidence from studies using the IPD–MD does not support the CO model. Nonetheless, in-group and out-group aggression not evolving together would be a premature conclusion given the uncertainty of whether out-group aggression in the IPD–MD (i.e., investment in the between-group pool) corresponds to the operationalization of this concept in the CO model. Thus, the present study argues the vital importance of revisiting whether the IPD–MD offers contextual cues to elicit out-group aggression that is arguably acquired during evolution.

Human minds are thought to have domain-general and domain-specific features [42, 43], and evolutionarily acquired psychological mechanisms are often characterized as domain specific [44]. For instance, the percentage of accuracy in performing logical reasoning tasks increases when the task is framed to detect norm violators [45, 46]. That is, “cheater detection” is thought to be an adaptive reasoning system specific to the domain of social exchange [47]. Previous studies have identified various domain-specific psychological systems [47], including theory of mind [48], intuitive physics [49], and folk biology [50]. Most importantly, intergroup bias is also considered a domain-specific feature [51].

Situational cues that imply a certain adaptive task reportedly activate a corresponding domain-specific mindset and behavior. An example is in the way disease priming, which induces pathogen infection threat assessment, leads to the preference for a symmetrical face, which indicates a high-functioning immune system [52], and negative attitudes toward immigrants, who are associated with the possibility of unknown pathogens [53, 54]. Cues of an important social exchange situation may also facilitate cooperation in a prisoner’s dilemma game [55, 56]. If intergroup bias stems from an evolutionarily acquired domain-specific mindset [51], then out-group aggression may be triggered by the cue of an adaptation task, such as intergroup conflict.

Choi and Bowles [15] described out-group aggressions predicted by the CO model as in-group-benefitting behavior. One of the main causes of intergroup conflicts is the competition for resources, such as food, territory, and mating opportunities [57–59]. The in-group-benefitting aspect of out-group aggression is an important tenet of out-group aggression in the CO model. Several evolutionary models and simulations have suggested that out-group aggression might evolve when individuals gain resources from an out-group [24, 60]. Moreover, people display hostile intergroup behavior when out-group resources can be acquired [61]; people also tend to be sensitive to threats arising from hostile intergroup relationships [62, 63]. These findings suggest that out-group aggression is favored when it benefits the in-group.

However, out-group aggression in IPD–MD seems to show a discrepancy with how it has been theoretically defined in the CO model. More specifically, previous studies using the IPD–MD have operationalized out-group aggression as simply reducing the payoff of out-group members: investment in the between-group pool is typically framed as merely about increasing and decreasing payoffs for in-group and out-group members, respectively [12]. Thus, the in-group-benefitting aspect of out-group aggression seems to be missing in the IPD–MD, and this might be why previous studies using the game have yielded inconsistent results with the CO model. In other words, if out-group aggression in an IPD–MD (i.e., investment in the between-group pool) is framed such that it leads to financial gain for the in-group, then out-group aggression would emerge, which provides empirical support for the CO model.

1.3 The present research

The present research aimed to test the effect of framing in an IPD–MD and examine whether out-group aggression would emerge when the contribution to the between-group pool is framed as having benefits to the in-group. More specifically, this study formulated two conditions that varied in the framing of the between-group pool: a control condition and a steal condition. In the former, the instructions on the two pools were identical to that of a basic IPD–MD. In the latter condition, the investment in the between-group pool was framed such that it led to stealing money from an out-group for their own group.

The current research tested two hypotheses regarding the framing effect on out-group aggression. Böhm [31] proposed the “weak” and “strong” hypotheses of out-group aggression based on the CO model: the amount invested in the between-group pool should be interpreted not only in terms of its absolute amount but also as a relative amount compared with the amount invested in the within-group pool, and “a larger contribution to the between-group pool relative to the within-group pool may be interpreted as negative attitude toward the out-group, an equal contribution to both pools as indifference regarding the out-group’s welfare, and a smaller contribution to the between-group pool as positive attitude toward the out-group” [13] (p. 2). Based on the CO model, a negative attitude toward the out-group can be expected to lead to aggressive behavior in the steal-framing condition. Therefore, the present study set the “strong” hypothesis (hypothesis S) as follows:

Hypothesis S: In the steal condition, individuals would contribute more to the between-group pool than to the within-group pool.

Even if hypothesis S is not supported, as in previous studies [36, 38, 40, 64], steal framing may nonetheless lead to a less positive attitude. Therefore, the current study set the “weak” hypothesis (hypothesis W) as follows:

Hypothesis W: Individuals in the steal condition would invest more money in the between-group pool than those in the control condition.

The research aimed to further explore how the steal framing would influence out-group aggression. Framing effects in experimental economic games can be divided into effects of changes in preference and belief [65]. Preference tends to be stable regardless of the actions and reactions of an interacting partner. Meanwhile, belief refers to an expectation about others’ behavior. If the framing affected the investment in an IPD–MD, then whether the effect would be attributable to changes in preferences and/or beliefs merits investigation.

2.1 Method

Study 1 was reviewed and approved by the ethical committee at Kochi University of Technology. In accordance with the Declaration of Helsinki, all participants provided written informed consent.

2.1.1 Participants

The study was advertised in a large student-participant pool at [redacted for peer review], and 72 participants (34 women) voluntarily participated in the current study. Their mean age was 19.53 years (SD = 1.12).

2.1.2 Procedure

Upon arrival at the experimental lab, participants were given a participant ID and instructed not to share it with anyone. They were then escorted individually to an experimental cubicle, in which they completed the study on a computer without the physical presence of others. Once they were seated, they received instructions about the IPD–MD. Participants were first randomly divided into two groups, and each was given 600 JPY by the experimenter. Next, they had a one-shot interaction in which they each decided how much of the 600 JPY to keep for themselves and to invest in the within- and inter-group pools. The amount invested in the within-group pool was doubled by the experimenter and the total was distributed equally to all members of the participants’ own group.

Participants were randomly assigned to one of the two framing conditions (i.e., the control and steal conditions) and received different instructions on the between-group pool. In the control condition, they were informed that the total amount invested in the pool would be doubled and then distributed equally among in-group members regardless of their contribution. Moreover, they were told that out-group members would lose half the amount of money that in-group members received. The instruction in the control condition was identical to that in a normal IPD–MD. To put it concretely, in a game between Groups X and Y, each of which has five participants, if Participant A from Group X invests 100 JPY in the between-group pool, then all participants in Group X, including participant A, would receive 40 JPY each, and 20 JPY are deducted from each of the five participants in Group Y. In the steal condition, the amount of money invested in the between-group pool would be equally distributed to all the members of the in-group. Moreover, the in-group members could steal the same amount of the money they receive from out-group members and distribute it to each in-group member. For example, if Participant A of Group X invests 100 JPY in the between-group pool, all members of Group X, including A, would receive 20 JPY each. They receive additional 20 JPY that is taken from out-group members. In other words, the amount of money deducted from Group Y is given to Group X. Thus, the payoff structure of each individual was identical in both conditions. The participants were told that all of them would decide simultaneously, and that they could complete the game only once. The experiment also emphasized that the rules of the game were the same for out-group members. After reading the instructions about the IPD–MD, the participants input their decisions on a computer screen.

The participants then completed a post-experiment questionnaire. They first answered the comprehension and manipulation check questions. The tool contained three comprehension check questions: C1) “Whose money does the investment in the within-group pool increase?” C2) “Whose money does the investment in the between-group pool increase?” and C3) “Whose money does the investment in the between-group pool increase?” They selected one of the following options: “increase (decrease) the money of my group as a whole,” “increase (decrease) the money of others’ group as a whole,” “increase (decrease) the money of both groups,” “increase (decrease) the money of neither group,” or “don’t know.” For the manipulation check, they were asked the following question: “Who received the money subtracted from the members of the other group owing to the investment in the between-group pool?” They answered this with one of the following options: “the money went to my group,” “the experimenter collected the money,” or “I don’t know.”

After the comprehension and manipulation checks, the participants inferred how other members of their own group and the other group had completed the game. More specifically, they were asked to indicate how much other members of their own group and other group had kept and invested in the within- and between-group pools, in units of 50 JPY. For exploratory analyses, the study administered items measuring identification with the in-group and out-group and social dominance orientation (see S4 for more details). Finally, the participants provided demographic information (e.g., sex and age), received rewards according to the results of the game, and were dismissed. The entire experiment took approximately 50 minutes.

2.2 Results

2.2.1 Comprehension and manipulation checks

The correct answer rates for C1, C2, and C3 were 97.3%, 91.8%, and 90.4%, respectively. The study found no significant differences in the correct response rate between conditions (Fisher’s exact tests: all ps >.05). The participants’ understanding of the rules of the game was satisfactory. The correct response rate for the manipulation check was 94.5%. In the control condition, 89.2% of the participants answered correctly, and 10.8% answered incorrectly or chose “I don’t know.” All participants in the steal condition answered correctly. The correct response rate between the two conditions showed no significant difference (Fisher’s exact test, p = .115). Given that most of the participants correctly answered the comprehension and manipulation check questions, the study did not need to carry out data exclusion. Data exclusion based on these questions did not change results in a meaningful manner (see S1 for more details).

2.2.2 Behavioral data analysis

On average, participants kept 397.26 JPY (SD = 191.10), invested 147.95 JPY (SD = 171.28) in the within-group pool, and invested 54.79 JPY (SD = 103.47) in the between-group pool. The means and standard deviations of their investments under different conditions are shown in Figure 1. Following Halevy et al. [12], the study conducted a 2 (framing: control vs. steal) × 2 (pool: within- vs. between-group) mixed ANOVA. The results showed a significant main effect of pool, F(1, 71) = 14.33, p <.001, η_p² = .17. The main effects of framing (F(1, 71) = 0.54, p = .465, η_p² = .01) and the interaction effect (F(1, 71) = 0.004, p = .953, η_p² < .001) were not significant.

2.2.3 Hypothesis testing

The mean amount of investment in the between-group pool was 45.94 JPY (SD = 100.95) in the control condition and 63.89 JPY (SD = 106.64) in the steal condition, with no significant difference between them (t(71) = 0.74, p = .46, d = 0.17). In the steal condition, the participants invested a significantly lower amount in the between-group pool than in the within-group pool (M = 155.56, SD = 159.81, t(35) = 2.75, p = .009, d = 0.68). Therefore, hypotheses S and W were not supported.

2.2.4 Inference about others’ behavior

Although the effect of the framing manipulation was not significant, the present study examined the participants’ inferences about other in-group and out-group members’ investment decisions (see Figures 2 and 3). In the control condition, the mean estimated amount of money that other in-group members kept for themselves was 377.03 JPY (SD = 144.14). The expected amount invested in the within- and between-group pools by other in-group members was 148.65 JPY (SD = 103.74) and 64.86 JPY (SD = 75.34), respectively. In the steal condition, the expected amount that other in-group members kept was 334.72 JPY (SD = 130.83). The estimated amount invested in the within- and between-group pools by in-group members was 163.89 JPY (SD = 93.05) and 91.67 JPY (SD = 84.09), respectively. A 2 (framing: control vs. steal) × 2 (pool: within- vs. between-group) mixed ANOVA on the estimated amount of money invested by in-group members revealed that the main effect of the pool was significant, F(1, 71) = 29.26, p <.001, η_p² = . 29. The main effect of framing (F(1, 71) = 1.90, p = .173, η_p² = .03) and the interaction effect (F(1, 71) = 0.16, p = .690, η_p² = .002) were not significant. Thus, the steal framing did not alter the expectation about how other in-group members would complete the game.

Regarding inferences on out-group members’ behavior, participants in the control condition expected that out-group members kept 360.81 JPY (SD = 159.05), invested 155.41 JPY (SD = 133.74) in the within-group pool, and invested 89.19 JPY (SD = 106.81) in the between-group pool. In the steal condition, the estimated amount that out-group members kept was 331.94 JPY (SD = 136.88). They expected out-group members to invest 195.83 JPY (SD = 99.55) and 83.33 JPY (SD = 75.59) in the within- and between-group pools, respectively. A 2 (framing: control vs. steal) × 2 (pool: within- vs. between-group) mixed ANOVA on the estimated amount of money invested by out-group members revealed a significant main effect of pool, F(1, 71) = 23.15, p < .001, η_p² = .25. The main effect of framing (F(1, 71) = 1.09, p = .299, η_p² = .02) and the interaction effect (F(1, 71) = 1.55, p = .217, η_p² = .02) were not significant. These results indicated that the framing did not alter the behavioral expectation of out-group members.

2.3 Discussion

Both hypotheses were not supported in Study 1: the results showed that steal framing did not increase out-group aggression in IPD–MD. Thus, even when out-group aggression was framed as being beneficial for the in-group, the CO model was not empirically supported.

Study 1 had fewer than 40 participants in each condition, smaller than the number of participants recruited in the majority of studies that used the IPD–MD [31, 38, 64]; except for Halevy et al. [40]. Thus, the present research conducted Study 2 with more participants and re-tested the hypotheses.

3.1 Method

Study 2 was reviewed and approved by the ethical committee at Kochi University of Technology. In accordance with the Declaration of Helsinki, all participants provided written informed consent.

3.1.1 Participants and procedure

Study 2 intended to recruit 50 participants for each condition. A total of 107 Japanese undergraduate students signed up for the study (53 females, 51 males, and 3 neither or respondent refusals). Their mean age was 18.87 years (SD = 1.18). Participants were recruited from a large participant pool at [redacted for peer review] with an emphasis on monetary incentives. The procedure and materials were identical to those in study 1.

3.2 Results

3.2.1 Comprehension and manipulation checks

The correct answer rates for the three comprehension check questions were 96.1%, 91.3%, and 94.2%. The two framing conditions showed no significant differences (Fisher’s exact test: all ps >.05). The correct response rate for the manipulation check item was 91.3%. In the control condition, 83.3% of the participants answered it correctly, and 16.7% answered it incorrectly or chose “I don’t know.” All (100%) of the participants answered correctly in the steal condition, and the difference was significant (Fisher’s exact test: p = .003). The exclusion of participants in the control condition who failed to answer the questions correctly did not change the results of subsequent analyses in a meaningful way. Thus, results without data exclusion are reported here (see S2 for analyses with data exclusion).

3.2.2 Behavioral data analysis

The participants, on average, kept 352.43 JPY (SD = 202.84) for themselves and contributed 156.31 JPY (SD = 170.31) and 91.26 JPY (SD = 150.72) to the within- and between-group pools, respectively (see Figure 2 for the descriptive statistics by condition). A 2 (framing: control vs. steal) × 2 (pool: within- vs. between-group) mixed ANOVA on the amount of investment revealed a significant main effect of pool (F(1, 101) = 7.72, p = .007, η_p² = .07) and a significant interaction effect (F(1, 101) = 4.06, p = .047, η_p² = .04). In contrast, the main effect of framing was not significant, F(1, 101) = 2.06, p = .154, η_p² = .02. Post hoc comparisons using the Holm method revealed that the amount of investment in the within-group pool was higher in the steal condition than that in the control condition (p = .014), but the difference in investment in the between-group pool between the two conditions was not significant (p = .518). In addition, the amount of investment between the within- and between-group pools in the control condition did not significantly differ (p = .581). Meanwhile, the difference in the steal condition was significant (p = .001).

3.2.3 Hypothesis testing

The mean amount of investment in the between-group pool was 100.93 JPY (SD = 156.76) in the control condition and 80.61 JPY (SD = 144.63) in the steal condition, with no significant difference between them (t(101) = 0.68, p = .497, d = 0.13). In the steal condition, the amount invested in the between-group pool was significantly lower than that in the within-group pool (M = 196.94, SD = 187.47, t(48) = 3.18, p = .003, d = 0.70). Therefore, hypotheses S and W were not supported.

3.2.4 Inference about others’ behavior

In the control condition, the in-group members kept a mean estimated amount of 337.04 JPY (SD = 158.17). Participants expected other in-group members to invest 152.78 JPY (SD = 115.09) in the within-group pool and 125.00 JPY (SD = 128.40) in the between-group pool. In the steal condition, in-group members expected their peers to keep 279.59 JPY (SD = 153.07) for themselves and estimated the latter’s investment of 218.37 JPY (SD = 134.90) in the within-group pool and 110.20 JPY (SD = 80.35) in the between-group pool. A 2 (framing: control vs. steal) × 2 (pool: within- vs. between-group) mixed ANOVA on the estimated amount of money invested by in-group members revealed that the main effect of pool (F(1, 101) = 15.32, p <.001, η_p² = .13) and the interaction effect (F(1, 101) = 5.36, p = .023, η_p² = .05) were significant. Meanwhile, the main effect of framing was not significant, F(1, 101) = 2.8, p = .097, η_p² = .03. Post hoc pairwise comparisons with the Holm method revealed that the level of inferred investment in the between-group pool was not different between the two framing conditions (p = .52). In contrast, that in the within-group pool in the steal condition was significantly higher compared with in the control condition (p = .005). These results showed that although steal framing increased the inference of cooperation among in-group members, it did not increase the inference that other in-group members would attack out-group members.

In the control condition, the out-group members estimated their peers to have kept 347.22 JPY (SD = 150.29) and invested 155.56 JPY (SD = 116.01) in the within-group pool and 120.37 JPY (SD = 126.09) in the between-group pool. In the steal condition, they expected out-group members to have kept 280.61 JPY (SD = 157.39) for themselves and invested 230.61 JPY (SD = 139.87) and 127.55 JPY (SD = 84.20) in the within- and between-group pools, respectively. A 2 (framing: control vs. steal) × 2 (pool: within- vs. between-group) mixed ANOVA on the estimated amount of money invested by out-group members revealed that the main effect of framing (F(1, 101) = 7.19, p = .009, η_p² = .07) and pool (F(1, 101) = 15.35, p <.001, η_p² = .13) were significant. The interaction effect was not significant (F(1, 101) = 3.7, p = .057, η_p² = .04). Thus, steal framing generated an inference that out-group members would no longer pursue self-interest, but this did not mean that they would invest more in out-group aggression.

3.3 Discussion

Study 2 showed the same patterns as those in Study 1. The amount of investment in the between-group pool in IPD–MD did not increase with steal framing and exceeded the amount invested in the within-group pool. These results were inconsistent with the CO model.

Given that Studies 1 and 2 employed identical procedures and study materials, the author combined the data from both experiments to increase the statistical power. The sample size was 176. The number of participants in the control condition was 91, and that in the steal condition was 85. They, on average, kept 371.02 JPY (SD = 198.74) for themselves and invested 152.84 JPY (SD = 170.27) and 76.14 JPY (SD = 134.05) in the within- and between-group pools, respectively (see Figure 1).

A 2 (framing: control vs. steal) × 2 (pool: within- vs. between-group) mixed ANOVA on the amount of investment revealed a significant main effect of pool, F(1, 174) = 19.66, p <.001, η_p² = 0.10. In contrast, the main effects of framing (F(1, 174) = 2.41, p = .122, η_p² = 0.01) and the interaction effect (F(1, 174) = 2.59, p = .109, η_p² = 0.02) were not significant.

The mean amount of money invested in the between-group pool was 78.57 JPY (SD = 138.87) in the control condition and 73.53 JPY (SD = 129.47) in the steal condition, with no significant difference between them, t(174) = 0.25, p = .804, d = 0.04. In the steal condition, participants invested significantly less in the between-group pool than in the within-group pool (M = 179.41, SD = 176.49, t(84) = 4.19, p <.001, d = 0.69). Therefore, hypotheses S and W were not supported.

4.1 Inference about others’ behavior

In the control condition, the mean estimated amount of money that other in-group members kept was 353.29 JPY (SD = 153.08), the amount invested in the within-group pool was 151.10 JPY (SD = 110.04), and the amount invested in the between-group pool was 100.55 JPY (SD = 113.41). In the steal condition, the mean estimated amount kept was 302.94 JPY (SD = 145.85), the amount invested in the within-group pool was 195.29 JPY (SD = 121.41), and the amount invested in the between-group pool was 102.35 JPY (SD = 81.98). A 2 (framing: control vs. steal) x 2 (pool: within- vs. between-group) mixed ANOVA on the estimated amount of money invested by in-group members revealed that the main effect of framing (F(1, 174) = 4.26, p = .041, η_p² = .02) and pool (F(1, 174) = 36.59, p <.001, η_p² = .17) were significant. The interaction effect was not significant (F(1, 174) = 3.19, p = .076, η_p² = .02).

In the control condition, the mean estimated amount of money that out-group members kept was 352.75 JPY (SD = 153.18), and that invested in the within- and between-group pools was 155.49 JPY (SD = 122.80) and 107.69 JPY (SD = 119.01), respectively. In the steal condition, the amount of money they expected out-group members to keep was 302.35 JPY (SD = 150.38), and that invested in the within- and between-group pools was 215.88 JPY (SD = 124.93) and 108.82 JPY (SD = 83.16). A 2 (framing: control vs. steal) × 2 (pool: within- vs. between-group) mixed ANOVA on the estimated amount of money invested by out-group members revealed that the main effect of framing (F(1, 174) = 7.22, p = .008, η_p² = .04) and pool (F(1, 174) = 36.39, p <.001, η_p² = .17) and their interaction effect (F(1, 174) = 5.33, p = .02, η_p² = .03) were significant. Multiple comparisons using the Holm method showed that the difference between the two framing conditions was not significant in the between-group pool (p = .95), but participants in the steal condition expected out-group members to invest more in the within-group pool, compared with the control condition (p = .001).

The current research tested the framing effect on out-group aggression in the IPD–MD. In both Studies 1 and 2, steal framing did not promote aggression toward out-group members, and individuals preferred in-group cooperation without harming out-group members regardless of the game framing. Thus, these studies did not provide support for the hypotheses that were based on the CO model.

Previous studies using experimental economic games, such as the public goods game, have shown that framing can change behavior [65–68]. In the IPD–MD, group framing promotes aggression toward out-group members [64]. Given that framing manipulations can affect behavior in the IPD–MD, the findings from the two studies can be interpreted as suggesting that a cue of out-group deprivation (i.e., stealing money from them) does not promote out-group aggression.

In the current study, regardless of the framing condition, the amount of investment in the between-group pool was not higher than that in the within-group pool, consistent with previous findings [14, 64]. These findings support another evolutionary model of intergroup bias, namely, bounded generalized reciprocity (BGR) [17, 22]. The BGR model holds that in-group bias is caused by cooperation with in-group members rather than aggression toward out-group members [20, 69, 70]. The BGR model assumes that people have an intuitive belief that indirect reciprocity exists within the in-group, and that acting cooperatively toward in-group members is of vital importance to establishing a good reputation. In contrast, individuals do not suppose that out-group members are part of the system of indirect reciprocity, and consequently, they are not motivated to display altruistic behavior to earn a reputation not only with respect to out-group members but also strangers. In other words, the BGR model assumes only that humans do not act altruistically toward out-group members, not that they proactively attack them. Although the current study did not aim to validate the BGR model, the results are consistent with the model.

Out-group aggression can emerge when it can defend an ingroup [71, 72]. For example, Böhm et al. [36] showed that, although not the framing manipulation, the amount of investment in the between-group pool increases when it can prevent attacks from the out-group. In addition, the framing instruction used in Weisel and Zultan [64], which supports the “weak hypothesis” in IPD–MD, seems to have an in-group defense-like phrase. Further research is needed to investigate whether out-group aggression can occur by setting framing characterized by a defensive function.

The CO model has been criticized not only for its theoretical assumptions [30, 73] but also for the conflicting empirical findings [72, 74, 75]. These do not necessarily mean, however, that humans have not evolutionarily acquired any aggressive tendency toward out-group members. There may be several types of out-group aggression [71, 76, 77], and as such, it will be necessary to examine theoretically and empirically what types of aggression are directed toward out-group members.

Acknowledgements

I would like to thank Nene Tabuchi and Kuniyuki Nishina for their support in conducting the experiments, Editage (www.editage.com) for English language editing, and Hirotaka Imada for his valuable comments on an earlier version of this manuscript. This work was supported by the JSPS KAKENHI grant number 17K13903 and 21H00934.

Author contribution

NM developed the research concept, created the experimental materials, conducted two experiments and data analysis, and drafted the manuscript.

Additional Information

Competing interests

The author declares no competing interests.

Preregistration

The author did not preregister the two studies.

Data Availability

The data associated with this research are temporarily available at [https://osf.io/f6jn8/?view_only=0c6f225cab0d49fcb4d6b5e9e8909421] (The original link contains information on the author).

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Null Results for the Steal-Framing Effect on Out-Group Aggression

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Abstract

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1 Introduction

1.1 Coevolutionary model of intergroup bias

1.2 Out-group aggression in the IPD–MD

1.3 The present research

2 Study 1

2.1 Method

2.1.1 Participants

2.1.2 Procedure

2.2 Results

2.2.1 Comprehension and manipulation checks

2.2.2 Behavioral data analysis

2.2.3 Hypothesis testing

2.2.4 Inference about others’ behavior

2.3 Discussion

3 Study 2

3.1 Method

3.1.1 Participants and procedure

3.2 Results

3.2.1 Comprehension and manipulation checks

3.2.2 Behavioral data analysis

3.2.3 Hypothesis testing

3.2.4 Inference about others’ behavior

3.3 Discussion

4. Combined Analysis

4.1 Inference about others’ behavior

5 General Discussion

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References

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