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THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 1 of 50
This paper has been accepted at the Journal of Economic Behavior and Organization. It may not exactly 1
replicate the final version published in the journal. It is not a copy of record. 2
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The Psychology of Intergroup Conflict: A Review of Theories and Measures 6
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Robert Böhm1,*, Hannes Rusch2,3, Jonathan Baron4 9
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1 School of Business and Economics, RWTH Aachen University, Germany 12
2 School of Business and Economics, University of Marburg, Germany 13
3 TUM School of Management, TU München, Germany 14
4 Department of Psychology, University of Pennsylvania, USA 15
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* Corresponding author: 18
Robert Böhm, School of Business and Economics, RWTH Aachen University, 52062 Aachen, 19
Germany, Phone: +49 241 8097000, Email: robert.boehm@rwth-aachen.de 20
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Abstract 21
We review psychological research on intergroup conflict. First, we outline psychological 22
perspectives on forms and functions of groups. Second, we present the most influential 23
psychological theories of intergroup conflict and describe their similarities and differences in 24
predicting individual prejudice, discrimination, and conflict engagement. Third, we review 25
popular measures of intergroup discrimination, including rating measures, behavioral 26
measures, and allocation tasks. Furthermore, we call for a refined semantic framework to 27
structure and differentiate between different measures of intergroup bias. Fourth, we highlight 28
several interventions that can de-bias intergroup relations and facilitate conflict resolution. 29
Lastly, we propose that research on the psychology of intergroup conflict may benefit from a 30
stronger interdisciplinary orientation regarding both theoretical perspectives and methods 31
used and point out promising avenues for future research. 32
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Keywords: Intergroup Conflict; Intergroup Bias; Discrimination, Conflict Resolution 34
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1. Introduction 35
Human prosociality is a Janus-faced phenomenon. Although cooperation within groups is 36
common, cooperation with outsiders is often impaired by prejudice, discrimination and spite. 37
Tensions between groups quickly arise and frequently escalate into intergroup conflicts. In 38
fact, intergroup conflicts have been with us for a long time (Esteban et al., 2012; Gat, 2015), 39
and also today conflict between countries, as well as between ethnic and religious groups 40
remains omnipresent. Taken together, wars and genocides have been estimated to account for 41
more than 200 million deaths in the 20th century (Rummel, 1994). More recently, in 2014 42
alone, 180,000 people died in intergroup violence worldwide and 20,000 individuals in 69 43
countries were killed in terrorist attacks (Institute for Economics & Peace, 2015). 44
Research on the cognitions, emotions, and motivations underlying intergroup conflict 45
has a long history in psychology. In fact, intergroup conflict has even been named the 46
“problem of the century” in social psychology (Fiske, 2002).1 This research has concerned 47
such diverse topics as perceptions of group membership, behavioral consequences of 48
categorizing oneself and others into groups, or the effects of situational and personality 49
differences on intergroup relations. Accordingly, as can be seen in Figure 1, there has been a 50
steady increase in the number of research articles focusing on topics related to intergroup 51
conflict in leading social psychology journals over the last 25 years. 52
1 Social psychology, as a sub-discipline of psychology, deals with human thoughts, feelings, and behaviors in
the actual of imagined presence of others. Since intergroup interactions are by definition social phenomena,
much psychological research dealing with intergroup conflict can be attributed to social psychology (but see
section 6.3 for research in cognitive psychology relevant to intergroup conflict, and Cameron et al., 2001, for a
review of research on the ontogeny of prejudice and discrimination in developmental psychology).
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Figure 1. Conflict-related papers published in some of the leading journals of (social) psychology, 1990-54
2015. Note. Web of Science search for terms ‘intergroup conflict’, ‘intergroup bias’, ‘ingroup bias’, 55
‘discrimination’, or ‘war’ in the publication titles of the journals Psychological Science, Journal of Personality 56
and Social Psychology, Journal of Experimental Social Psychology, Personality and Social Psychology Bulletin, 57
European Journal of Social Psychology. 1990 was selected as start point as Psychological Science began 58
publishing then. 59
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After a brief introduction to the terminology used in psychological research on forms 61
and functions of social groups (section 2), this paper provides an overview of selected 62
psychological theories of intergroup conflict (section 3). Naturally, we cannot review this 63
abundant literature exhaustively. Rather, we focus on those theories and pioneering empirical 64
works that have emerged as the most influential ones in the literature. Second, we provide a 65
structured overview of the measures used to assess conflict-related individual attitudes and 66
behaviors (section 4). Third, we suggest a refined way of classifying phenomena relevant to 67
the study of intergroup conflict (section 5). To this end, we outline how the ‘social semantics’ 68
developed by West and colleagues (West et al., 2007) could be extended by a group-69
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membership dimension. Such ‘social group semantics’ may provide a useful framework for 70
structuring and connecting previous and future research. Finally, we summarize important 71
empirically informed interventions that can be used to de-bias intergroup relations (section 6). 72
2. Prologue 73
2.1 Definitions of Groups 74
Humans are a group-living species. In modern times, we grow up in family groups, study in 75
classes, work in teams, do team sports ourselves or support sports teams as members of fan 76
clubs. Moreover, we are all members of national and ethnic groups, gender groups, and 77
cultural groups. Most of us see ourselves as belonging to several groups at the same time. But 78
what exactly is a group? A very broad psychological definition defines a group “as two or 79
more individuals who are connected to one another by social relationships” (Forsyth, 2014, p. 80
3). As is common in the psychological literature, we will use the label ‘in-group members’ to 81
refer to those individuals who share a given group membership with the target individual and 82
‘out-group members’ to refer to individuals who are members of other groups, i.e., who do 83
not share that group membership with the target individual. 84
Different characteristic features of groups have been used to define what constitutes a 85
group. These include structural, rather objective characteristics like outcome interdependence. 86
In this view, whether a set of individuals represents a group depends on how these 87
individuals’ outcomes of social interaction relate to each other. Such outcome 88
interdependence can vary in degree (weak vs. strong) and type (positive vs. negative). For 89
instance, strong positive interdependence between individuals can create a ‘common fate’ 90
(Lewin, 1948), which, in turn, can lead to group formation by the respective individuals. 91
Likewise, differentiated but interdependent roles, such as the possibility for some individuals 92
to control the scope of action of other individuals or their outcomes (Sherif and Sherif, 1969), 93
may also prompt group formation. Other definitions rest on more subjective aspects like 94
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identifying oneself as belonging to a certain group and/or being recognized as a member of 95
that group by others (Brown, 1988; Tajfel, 1981). Cues that may lead to such social 96
identification range from minimal, apparently meaningless criteria (e.g., similar preferences 97
for paintings; Tajfel et al., 1971) to shared firm beliefs (e.g., moral views regarding issues 98
such as refugees or abortion; Parker and Janoff-Bulman, 2013). 99
2.2 Perceptions of Groups 100
The ability to differentiate between different groups as well as to identify oneself as a member 101
of certain groups relies on a number of socio-cognitive principles. Humans can categorize 102
themselves at various levels of abstraction, for example as a singular and independent 103
individual (called ‘personal identity salience’) or as part of an inclusive social category 104
(‘social identity salience’). At the highest (superordinate) level of abstraction, neither the 105
personal nor the social identity is salient, but all humans are perceived as belonging to a 106
single category, which is then set off against non-human animals. Accordingly, personal 107
identity is defined as those aspects of the self that make an individual unique, whereas social 108
identity is thought of as those characteristics of the self that classify it in relation to social 109
categories. Importantly, interacting individuals can perceive the exact same objective 110
interaction very differently, depending on which level of categorization is salient for them at 111
the moment. For example, the interaction of two individuals can be represented as an 112
interindividual interaction (i.e., two unique individuals), as an intragroup interaction (i.e., two 113
members of the same group) or as an intergroup interaction (i.e., two members of different 114
groups). This observation is important for understanding why much psychological research on 115
intergroup conflict investigates individuals or dyads, while trying to activate and manipulate 116
these individuals’ personal vs. social identity salience. 117
Building on cognitive principles of categorical perception, the social categorization 118
processes just described have been analyzed further in self-categorization theory (Turner et 119
al., 1987). According to this theory, individuals can differ in their ‘relative accessibility’, i.e., 120
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in their abilities to cognitively access the different levels of categorical abstraction, 121
depending, for example, on their past experiences, expectations, current goals or motives. For 122
instance, snowboarders may be ready to differentiate between skiers and snowboarders 123
whereas someone who is not interested in winter sports may perceive skiers and 124
snowboarders as a single social category. 125
The theory further poses that social categorization also depends on ‘comparative fit’, 126
i.e., different social identities are easier to distinguish when the difference within social 127
categories is perceived as small, compared to the difference between social categories (the so-128
called ‘meta-contrast principle’). For instance, in the presence of a skier, a snowboarder might 129
categorize another snowboarder as an in-group member and the skier as an out-group 130
member. But in the presence of a skier, a snowboarder, and a swimmer, the snowboarder 131
might categorize the skier and the snowboarder as in-group members and the swimmer as an 132
out-group member. 133
Lastly, self-categorization theory assumes that in addition to relative accessibility and 134
comparative fit, ‘normative fit’ may influence the categorization process. To evaluate 135
normative fit, a target individual’s attributes and behaviors are compared to own expectations 136
about what ordinary in-group members and ordinary out-group members are likely to be and 137
act like. 138
Beyond the principles of mere social categorization, perceptions of the cohesiveness of 139
different groups (by both group members and outsiders) can differ substantially. Even if a set 140
of people meets all criteria for what constitutes a group, groups can still differ in how strongly 141
they are perceived as cohesive units, i.e., groups can differ in ‘entitativity’ (Campbell, 1958). 142
Interaction frequency, common goals and outcomes, group member similarity, and subjective 143
importance of the group are all related to perceptions of entitativity, whereas factors like 144
group size, continuance, and permeability of group boundaries are less important (Lickel et 145
al., 2000). Based on their level of entitativity, groups have been categorized as ‘intimate 146
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groups’ and ‘task groups’, both with high entitativity, ‘social categories’ with medium 147
entitativity, or ‘loose associations’ with low entitativity. Judgments of a group’s entitativity, 148
in turn, are likely associated with perceptions of and reactions to intergroup conflict (Lickel et 149
al., 2001; Stenstrom et al., 2008). 150
2.3 Functions of Groups 151
Although these approaches to the study of group formation and reactions to group 152
membership differ in their subtleties, they all agree that the group dimension of social 153
interaction is an integral part of human cognition and behavior. They all take for granted that 154
humans have a tendency to readily identify with and interact within groups. In light of the 155
evolutionary history of our species, many scholars argue, this is not surprising, as homo 156
sapiens was not the first to discover and reap the benefits of group living. Likely, already the 157
common ancestors of humans and chimpanzees or even earlier species in our lineage did so 158
(see e.g., Glowacki et al., in press, this issue). Obviously, living in self-organized groups can 159
have crucial advantages compared to being on one’s own (e.g., Brewer and Caporael, 2006; 160
Wilson, 2012). Hunting and protection against natural hazards or conspecific enemies, for 161
example, are more effective if carried out by a group. More generally, task sharing and 162
specialization within groups yield efficiency advantages. Thus, it is likely that human 163
psychology is adapted to group living (Tooby and Cosmides, 2010). 164
In line with this evolutionary perspective, psychological research has shown that 165
humans have a ‘need to belong’, i.e., an inherent desire to be accepted as a group member, 166
and thus to be part of a greater social unit with positive and stable relationships (Baumeister 167
and Leary, 1995). Accordingly, humans are prone to bond and synchronize with others who 168
are physically and psychologically similar, which is particularly important for the question of 169
whom they form groups with. Moreover, there is some indication that a lowered sense of 170
belonging is associated with depression (e.g., Pittman and Richmond, 2007) and suicidal 171
behaviors (Joiner et al., 2002). The need to belong is also related to the individual tendency to 172
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conform, i.e., to match attitudes, beliefs, and behaviors to group norms, under both 173
informational uncertainty (‘informational influence’, i.e., individuals conform to other group 174
members when they do not know what is ‘right’ or ‘wrong’; e.g., Sherif, 1936) and certainty 175
(‘normative influence’, i.e., individuals conform to other group members despite knowing that 176
this is ‘wrong’; e.g., Asch, 1951). Normative influence is stronger, for example, when the 177
individuals’ own group is in competition with another group (Deutsch and Gerard, 1955). 178
Furthermore, normative influence is stronger when individuals are observed by in-group 179
members, whereas informational influence is stronger when individuals act in private (for a 180
meta-analysis, see Bond, 2005). Hence, individuals’ need to belong lays the psychological 181
groundwork for shared beliefs, values, and norms, all of which are important features of many 182
groups. 183
Being connected to others in a group also comes with the risk of being exploited, 184
though, because actions in the interest of the in-group often involve costs for the individual 185
group member (e.g., Bornstein, 2003). The interplay of individual costs and benefits that 186
eventually leads to either effective and stable groups or the dissolution of unstable groups is 187
described in social exchange theory (Thibaut and Kelley, 1959). In a similar vein, optimal 188
distinctiveness theory (Brewer, 2003) describes a continuum between individual uniqueness 189
(i.e., differentiation from others) and psychological homogeneity (i.e., assimilation to others) 190
and states that an optimal distinctiveness level exists that satisfies both these opposing needs. 191
Optimal distinctiveness theory concedes, however, that this optimal level can differ among 192
individuals because of different cultural norms and individual socialization. Thus, optimal 193
distinctiveness theory provides a more general psychological framework for the level of 194
identification with different in-groups, both in terms of selection and strength, as well as the 195
need for differentiation from out-groups. 196
In summary, groups are units of two or more people connected through social 197
relationships, often accompanied by a positive interdependence in goals and outcomes, as 198
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well as a social hierarchy. Perceptions of others as in-group or out-group members are the 199
result of a cognitive categorization process. Everyone belongs to various groups that may 200
differ in their level of perceived entitativity. Becoming a member of and conforming to stable 201
groups, as well as differentiating the in-group from other groups, is an integral characteristic 202
of human psychology. In the next section, we introduce and summarize major psychological 203
theories that describe the relations between groups, and hence, the causes of intergroup 204
conflict. 205
3. Intergroup Conflict 206
3.1 Definition and Types of Intergroup Conflict 207
From a psychological perspective, broadly defined, intergroup conflict is the perceived 208
incompatibility of goals or values between two or more individuals, which emerges because 209
these individuals classify themselves as members of different social groups. Several scholars 210
have suggested distinguishing between different types of conflict. For instance, conflicts have 211
various sources. They can arise over (scarce) economic resources (e.g., money, territory), 212
values (e.g., what is ‘right’ and ‘wrong’), power (e.g., influence on the other party’ behaviors 213
or outcomes), or a combination of these (Katz, 1965). Moreover, conflicts can be located on a 214
scale ranging from tractable to intractable conflicts (Bar-Tal, 2011). Tractable conflicts 215
concern goals of low importance that are partially compatible and partially incompatible 216
between the involved parties (‘mixed-motive’ situations). Hence, they are likely to be 217
resolved quickly and are rather short-lived. Intractable conflicts, in contrast, concern goals of 218
high importance (e.g., resources indispensable for the group’s existence) and are perceived as 219
unsolvable (‘zero-sum’ situations). Intractable conflicts often have a longer duration than 220
tractable ones, leading to a history of hostility between the parties involved. 221
3.2 Psychological Theories of Intergroup Conflict 222
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Intergroup conflict affects the perceptions (e.g., stereotyping, prejudice), emotions (e.g., fear, 223
hate), and behaviors (e.g., discrimination, aggression) of the individuals involved. A plethora 224
of theories have been proposed to explain this ‘psychology of intergroup conflict’. In this 225
section, we largely ignore differences in the methods used to test these theories (but see the 226
next section for an overview). Rather, we focus on the underlying processes assumed to be 227
responsible for positive discrimination against in-group members and negative discrimination 228
against out-group members. Note that the following overview of theoretical accounts is by no 229
means exhaustive. Instead, we focus on the most influential accounts from a historical 230
perspective. In addition, we include several more recent accounts that appear to us as being of 231
particular interest for an interdisciplinary audience. 232
3.2.1 Personality Theories 233
After WWII, scholars tried to explain how people could actively engage in, or willingly 234
accept, the cruelties of the Holocaust. In their famous book The Authoritarian Personality 235
(1950), the sociologist Theodor W. Adorno and his colleagues argued that such a fascistic 236
potential must be rooted in a dysfunctional personality syndrome, that is, a certain 237
combination of basic personality traits. The most important of these traits was assumed to be 238
authoritarianism, which is characterized by the belief in absolute obedience or submission to 239
an authority, leading to the (acceptance of) oppression of subordinates. Adorno et al. (1950) 240
proposed that the authoritarian personality develops in early childhood as a result of 241
hierarchical and authoritarian parent-child relationships. Accordingly, children who are 242
strongly dominated and threatened by their parents should be more likely to develop an 243
authoritarian personality. 244
Later research refined the concept, renamed it as ‘right-wing authoritarianism’ (RWA; 245
e.g., Altemeyer, 1998), and particularly focused on its psychometric assessment. Empirical 246
research using respective questionnaires showed that people who score high on RWA are 247
more favorable of punishment and control of norm deviators (Narby et al., 1993). Moreover, 248
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it was found that RWA correlates positively with prejudice against ethnic and racial 249
minorities (e.g., Duckitt and Farre, 1994). 250
Another individual difference variable that seems important for an individual’s 251
proneness to be prejudiced and discriminatory toward out-groups is ‘social dominance 252
orientation’ (SDO; Sidanius and Pratto, 2001). SDO predicts an individual’s endorsement of 253
in-group dominance and a general orientation toward group-based inequality (Ho et al., 254
2015). Social dominance theory provides a psychological explanation of support for group-255
based social hierarchies. According to this perspective, group-based hierarchies can be age-256
based, gender-based, or based on more arbitrary characteristics (e.g., race, ethnicity, religious 257
affiliation, sexual orientation). These hierarchies assign more power and higher status to 258
people at the top (e.g., older people in age-based hierarchies, men in gender-based 259
hierarchies). In such hierarchies, discrimination is legitimized by culturally shared ideologies. 260
There are legitimizing beliefs, captured by SDO, that enhance the hierarchy and therefore 261
intergroup inequality (high SDO; e.g., racism) or attenuate the hierarchy and therefore 262
increase intergroup equality (low SDO; e.g., diversity). 263
Note that measures of RWA and SDO are typically moderately positively correlated, 264
but recent meta-analytical evidence suggests that they are largely independent and operate via 265
different psychological processes (Perry et al., 2013; Sibley and Duckitt, 2008). However, 266
SDO and RWA share a major limitation with all purely personality-based approaches: 267
situational factors are largely ignored (e.g., relationship and interdependence between 268
groups). Other theoretical approaches therefore focus more on the identification of situational 269
factors that may increase individuals’ willingness to engage in intergroup conflict, while 270
conceding that personality characteristics may have a moderating role in this process. 271
3.2.2 Realistic Group Conflict Theory 272
Muzafer Sherif and his colleagues, for instance, proposed a highly influential situation-based 273
perspective on intergroup conflict. Based on Campbell’s (1965) original formulation, Sherif’s 274
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realistic group conflict theory states that prejudice and discrimination are the result of 275
competition over limited resources between groups (e.g., money, power, social status; Sherif, 276
1966). Such a negative interdependence in the groups’ (incompatible) goals leads to a zero-277
sum representation of intergroup interactions in which the strength of perceived conflict 278
depends on the level of negative group interdependence (i.e., the scarcity of the contested 279
resources). In contrast, if groups have a positive interdependence, e.g., because they need to 280
jointly work on a task to reach a superordinate goal, intergroup relations are positive. Hence, 281
realistic group conflict theory identifies the causes of intergroup conflict in external and 282
‘realistic’ factors, i.e., actual needs. 283
Realistic group conflict theory is based on one of the most famous social psychological 284
study series – the Robber’s Cave experiments (Sherif et al., 1961; Sherif and Sherif, 1953). 285
These field experiments took place at Robber’s Cave State Park (Oklahoma, US). One of the 286
studies involved 20 twelve-year-old boys who were unknown to each other but had a similar 287
family background (white, middle-class, protestant). The boys were randomly assigned to two 288
groups and separately brought to the study site without awareness of the existence of the other 289
group. In the first stage of the experiment (in-group formation), the groups had to complete 290
some joint within-group tasks that required cooperative planning and execution (e.g., carrying 291
a canoe through rocky terrain). The boys also chose names for their groups and decorated 292
flags and shirts with these names. This stage aimed to create some identification with and 293
attachment to the own group. In the second stage (friction phase), the groups were made 294
aware of each other and competed over resources (e.g., in tug-of-war contests). That is, 295
members of just the wining team received prizes (e.g., a pocket knife). Out-group hostility 296
increased, starting with name-calling and culminating into burning the opponents’ flag and 297
stealing out-group members’ private property. In fact, this stage was cut short because the 298
hostilities between the groups became too intense. In the third and final stage of the 299
experiment (integration phase), the researchers introduced superordinate goals that could be 300
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achieved only by joint collaboration between the two groups (e.g., repair of the common 301
drinking water supply). Subsequently, the experimenters observed a slow but substantial 302
increase of positive intergroup relations (e.g., joint activities in the evening). Hence, these 303
findings provide support from an ecologically valid experiment that competition over limited 304
resources between groups may lead to severe perceived intergroup conflict, even among 305
otherwise ‘normal’ individuals. Despite potential criticism that may be raised regarding 306
ethical issues of the Robber’s cave experiments and its generalizability to (male and female) 307
adults, Sherif’s studies certainly had a great impact on the understanding of the psychology of 308
intergroup conflict. 309
3.2.3 Social Identity Theory 310
Henry Tajfel and John Turner’s social identity theory (Tajfel and Turner, 1986, 1979) stands 311
in stark contrast to realistic group conflict theory. It proposes that prejudice and 312
discrimination occur naturally when an individual categorizes someone else as a member of 313
an out-group. Accordingly, competition over resources is not necessary to induce intergroup 314
conflict. Even Sherif’s own investigations at Robber’s Cave indicated that children showed a 315
preference for engaging in intergroup competition once they learned about the existence of the 316
other group, even before the actual intergroup conflict games started. Thus, negative 317
interdependencies between groups appear as a sufficient but not as a necessary factor for 318
discriminatory preferences to be revealed. Accordingly, social identity theory is closely 319
related to self-categorization theory (Turner et al., 1987; see section 2.2). It rests on the idea 320
that individuals represent themselves either as an individual or as a group member depending 321
on their currently activated level of categorization. In the state of a salient social identity, 322
individuals are motivated to increase ‘positive distinctiveness’, that is, a positive self-concept 323
due to a favorable comparison of their in-group to an out-group on relevant dimensions.2 324
2 The importance of relative intergroup comparisons is also stressed in relative deprivation theory (Gutt, 1970;
Runciman, 1966). According to this rather sociological account, collective (or fraternal) relative deprivation
results from social comparisons of the in-group with out-groups when the own group receives less of a valuable
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Social identity theory proposes a direct link between a positive social identity and self-esteem, 325
achieved through the in-group’s relative standing.3 Individuals can follow different strategies 326
to achieve positive distinctiveness. When group boundaries are permeable (i.e., individuals 327
are able to change group membership), individuals may use ‘individual mobility’ to maximize 328
positive distinctiveness. For instance, I may look for a new sports team to cheer if my current 329
team is chronically unsuccessful. If group boundaries are perceived as impermeable and 330
group relations as rather stable, however, ‘social creativity’ strategies are predicted. For 331
instance, group members of the lower-status group may draw comparisons on a new 332
dimension that is more favorable for the in-group (e.g., the own company may sell fewer 333
products than the direct market competitor but is more socially and environmentally 334
sustainable) or change the comparison standard (e.g., a soccer team that is less successful in 335
international competitions may compare with national competitors). Lastly, if group 336
boundaries are stable but group relations are considered to be unstable, individuals may 337
engage in ‘social competition’. By discriminating against out-group members, the relative 338
standing of the in-group increases and social identity is boosted. Thus, although the 339
discriminatory consequences of social comparisons are the most prominent part of social 340
identity theory, discrimination is predicted only in specific circumstances, as just described.4 341
The predictions of social identity theory – in particular the social competition strategy – 342
have been tested in numerous experiments (for reviews, see e.g., Hogg et al., 2004; Hornsey, 343
2008). Noteworthy are Tajfel and colleagues’ own experiments using the so-called ‘minimal 344
resource than it is perceived to be entitled to receive, leading to feelings of injustice and dissatisfaction.
Collective
3 As an alternative process, uncertainty-identity theory (Hogg, 2000) suggests that not the increase of self-
esteem but the reduction of individual uncertainty in subjectively relevant domains may increase the likelihood
of social categorization and intergroup discrimination.
4 Note that a salient categorization on the collective level (Turner et al., 1987, see section 2.2) should in
principle eliminate any form of intergroup discrimination between members of former subcategories. However,
research on in-group projection (for a review, see Wenzel et al., 2007) has shown that different group
memberships are used as a frame of reference for a common (collective) superordinate group (i.e., the own group
is perceived as more prototypical for the superordinate group). As a consequence, intergroup discrimination may
still appear because the in-group is represented as a ‘better’ prototype of the higher-level collective formation
and out-group members are perceived to deviate from the desired characteristics of the superordinate category.
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 16 of 50
group paradigm’ (Tajfel et al., 1971; for an overview, see e.g., Brewer, 1979). In this 345
experimental setup, participants are divided into two groups based on trivial criteria. For 346
example, in the most famous version, participants state their preference regarding paintings by 347
Wassily Kandinsky and Paul Klee. Afterwards, they are assigned either to the “Kandinsky 348
Group” or the “Klee Group”, both of which allegedly consist of individuals who share the 349
same stated aesthetic preference.5 In the next step, participants take part in a resource 350
allocation task in which they have to distribute valuable points between an unknown in-group 351
member and an unknown out-group member (identified via numbers, e.g., “Klee Group 352
member no. 12”). Hence, the minimal group procedure excludes influences like 353
communication, stereotypes based on real groups, history of conflict, status hierarchies, or 354
shared fate of in-group members. Over several experiments, it was shown that – although 355
fairness in resource allocations between in-group and out-group members plays an important 356
role – participants tended to maximize the in-group member’s absolute gain (at cost to the 357
out-group member). Furthermore, and in line with social identity theory, participants were 358
willing to accept an absolutely lower gain for the in-group member when the out-group 359
member’s gain was reduced even more as a result. 360
3.2.4 Integrated Threat Theory 361
Integrated threat theory (Stephan and Stephan, 2000) considers both structural (e.g., scarce 362
resources) and psychological (e.g., social categorization) sources of intergroup conflict. Its 363
main focus is on the conditions leading to individual perceptions of threat that affect attitudes 364
and behaviors. The theory distinguishes between personal and intergroup threat. Personal or 365
self-directed threat concerns the individual’s own resources or personal identity. In contrast, 366
5 In fact, participants are either randomly assigned to one of the groups or all participants are assigned to the
same group. This excludes the potential confound that real differences in preferences between groups exist. For
minimal group procedures that do not rely on deceiving participants, see e.g., Böhm et al., 2013; Chen and Li,
2009; Güth et al., 2009.
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intergroup threat puts the whole group’s freedom, beliefs, or other characteristics under attack 367
or at risk. 368
There are different forms of threat. In line with realistic group conflict theory (Sherif, 369
1966; see section 3.2.2), realistic threat is the perception of material resource threat, e.g., risk 370
to the in-group’s safety, economy, politics, or well-being. In line with social identity theory 371
(Tajfel and Turner, 1986, 1979; see section 3.2.3), symbolic threat, on the other hand, 372
concerns non-material goods like the in-group’s morals, values, norms, attitudes, and esteem.6 373
These considerations lead to a two (target of threat: individual vs. in-group) by two (form of 374
threat: realistic vs. symbolic) matrix, with each combination evoking different consequences. 375
Threat appraisals to the group are assumed to evoke anger, whereas personal threats are likely 376
to evoke fear. Realistic threat causes feelings of insecurity and frustration, whereas symbolic 377
threat tends to cause emotions that devaluate the out-group (e.g., contempt, disgust). In 378
general, the more credible a certain type of threat is perceived, the greater the perceived stake 379
size and the immediacy of the behavioral/emotional reaction. For instance, intergroup threat 380
has been shown to increase the likelihood of negative stereotyping, distorted perceptions of 381
the out-group’s intentions, and even the dehumanization of out-group members (for a meta-382
analysis, see Riek et al., 2006). In addition, reactions also depend on the power of the 383
threatened group. High power groups may perceive themselves vulnerable and react with 384
more forceful measures, including direct intergroup violence. Low power groups, in contrast, 385
may react more carefully so as not to risk retaliation; they rather take indirect 386
countermeasures like sabotage, non-violent protest, and disobedience (Stephan and Stephan, 387
2000). 388
In summary, integrated threat theory provides a broader perspective on the role of 389
intergroup (and personal) threat perceptions. It stresses the importance of both realistic and 390
6 Note that perceptions of realistic and symbolic threat are typically moderately correlated, although they have
unique relations to out-group attitudes (Riek et al., 2006). Not surprisingly, realistic threat may lead to symbolic
threat (e.g., to justify conflict) and vice versa.
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 18 of 50
symbolic threats for the emergence of intergroup conflict. As such, integrated threat theory 391
demonstrates how negative intergroup behaviors may result from both structural and 392
psychological factors. Moreover, in a revised version of the theory (Stephan and Renfro, 393
2002), interindividual personality differences like SDO (Sidanius and Pratto, 2001; see 394
section 3.2.1) but also cultural differences are considered as variables that can affect the 395
perception of threats. 396
3.2.5 Theory of Bounded Generalized Reciprocity 397
Experimental work testing the predictions of social identity theory has repeatedly found that 398
mere categorization of individuals as in-group and out-group members can produce 399
intergroup discrimination, mostly in the form of in-group favoritism (see section 3.2.3). 400
Complementing the proximate explanations that social identity theory offers for these 401
observations, bounded generalized reciprocity theory (Yamagishi et al., 1999) suggests to also 402
take a cost/benefit-perspective into account. It stresses that belonging to groups that are 403
characterized by high levels of intragroup trust and cooperation has material advantages for 404
its members. Therefore, bounded generalized reciprocity theory poses that in-group members 405
are more likely to cooperate with each other in order to maintain a positive reputation, such 406
that they can continue to benefit from belonging to the group. More generally, Yamagishi and 407
colleagues argue that social groups are a container of expectations, in that individuals expect 408
positive reciprocity from in-group members by default but less so, or not at all, from out-409
group members (Yamagishi et al., 1999; Yamagishi and Mifune, 2009). The higher the 410
perceived entitativity of a group (see section 2.2), the more this container is filled with 411
expectations of generalized reciprocity (Yamagishi and Kiyonari, 2000).7 It is further 412
proposed that such group-bounded favoritism occurs only if individuals expect direct or 413
indirect reciprocity from fellow in-group members. In other words, it is the individuals’ 414
7 Note that there is evidence that social categorization may also cause perceptions of reciprocity between in-
group members (Platow et al., 2012). Hence, structural interdependences, social categorization, and perceptions
of reciprocity can (to a certain degree) mutually affect each other.
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 19 of 50
motivation to maximize material self-interest that leads to intergroup discrimination. As such, 415
the theory aims at explaining differences in individuals’ willingness to cooperate with in-416
group compared to out-group members, rather than providing an explanation for negative and 417
hostile behaviors toward out-group members. 418
To support this theoretical perspective, Karp et al. (1993) conducted an experiment in 419
which participants had to allocate resources between an in-group and an out-group member 420
(after minimal groups had been created, see section 3.2.3). The crucial experimental 421
manipulation consisted in whether the participants’ own outcome was a fixed amount – 422
independent of their allocation decision and therefore explicitly excluding the possibility of 423
reciprocity between in-group members – or depended on another in-group member’s 424
allocation decision. Thus, the latter condition incorporated indirect interdependence between 425
in-group members in the form of mutual (or multilateral) fate control (see Thibaut and Kelley, 426
1959). Karp et al. (1993) observed in-group biased allocations (i.e., giving more resources to 427
the in-group compared to the out-group member) when participants were in an interdependent 428
relationship with their in-group members, but not when their outcomes were fixed. In a 429
similar vein, other studies found substantial reductions of in-group favoritism when the 430
allocator in a dictator game knew that the recipient would not be informed about the 431
allocator’s group membership (Ockenfels and Werner, 2014; Yamagishi et al., 1999). 432
A recent meta-analysis compared the differential predictions of social identity theory 433
and the theory of bounded generalized reciprocity (Balliet et al., 2014), finding that 434
reciprocity concerns have an independent and additional explanatory value for the emergence 435
of intergroup discrimination in the domain of cooperative behavior (over and above mere 436
social categorization). Importantly, the meta-analysis by Balliet et al. (2014) found an overall 437
small to medium effect size indicating that cooperation with and prosociality toward in-group 438
members (in games like the dictator game, prisoner’s dilemma, public goods, and trust game) 439
is larger than toward out-group members. Moreover, no significant differences in the extent of 440
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 20 of 50
such discrimination between artificial (minimal) vs. natural groups, country of the 441
participants, and sex of the participants were found (although there is a tendency that men are 442
more likely to engage in intergroup conflict and discrimination, see e.g., McDonald et al., 443
2012). 444
3.2.6 The Co-Evolutionary Theory of Parochial Altruism 445
A prominent evolutionary approach to explaining why humans so readily discriminate against 446
out-groups is the theory of parochial altruism as arising from intergroup conflict (Choi and 447
Bowles, 2007; for overviews, see De Dreu et al., 2014; Rusch, 2014; Yamagishi and Mifune, 448
2016). The theory aims to explain our readiness to incur high individual costs in order to 449
promote in-group success in competitions with out-groups as an adaptation to the high-450
conflict environments humans were exposed to in ancestral times (Glowacki et al., in press, 451
this issue). The theory assumes that collective action against enemies resembles a public good 452
problem from the in-group’s perspective: contributions to the own group’s success are costly 453
to the individual (e.g., risk of injury or death in violent intergroup conflict) but the outcomes 454
of the collective action (i.e., winning or losing an intergroup competition) are shared among 455
all group members, irrespective of their individual contribution (but see, Rusch, 2014, 2013; 456
Rusch and Gavrilets, in press, this issue). Accordingly, ‘parochial altruism’ in the context of 457
this theory describes individual behavior that is (i) costly to the target individual, (ii) 458
beneficial for the target’s in-group, and (iii) costly for members of an out-group, all at the 459
same time (Choi and Bowles, 2007). Unlike other theories, this account assumes that an 460
individual’s contribution to intergroup conflict does not need to be compensated through 461
direct or indirect benefits for the contributing individual, i.e., that fighting for the in-group 462
may represent true altruism (Bowles, 2008). Using mathematical models supposedly 463
approximating the demographic conditions of the late Pleistocene/early Holocene, proponents 464
of co-evolutionary parochial altruism theory then suggest that high levels of violent 465
intergroup encounters and moderate levels of migration and gene flow between groups may 466
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 21 of 50
have favored a co-evolution of altruistic and parochial behavioral traits, that is: human 467
altruism and belligerence may have evolved through mutually reinforcing each other (Bowles, 468
2009; Choi and Bowles, 2007; García and van den Bergh, 2011; for a review, see Rusch, 469
2014). 470
In recent years, psychologists and other social scientists have begun to test 471
experimentally how individuals react to different configurations of individual, group, and 472
collective interests in situations of intergroup conflict, putting the proposed relationship of 473
altruism, parochialism, and conflict engagement under scrutiny. Their findings are mixed: 474
some studies found a positive correlation between individual-level prosociality and the 475
participation in intergroup conflict that benefits the in-group while harming the out-group 476
(e.g., Abbink et al., 2012), whereas others found quite the opposite (De Dreu, 2010; 477
Thielmann and Böhm, 2016; for further evidence and discussions, see Rusch et al., 2016). 478
Additional findings suggest that structural conditions are more important drivers of intergroup 479
aggression than personality traits like altruism or parochialism. For instance, individuals were 480
found to be more likely to engage in individually costly aggression against out-groups if the 481
in-group is perceived to be in a defensive (vs. offensive) position (i.e., ex ante protection 482
against potential out-group harm; Böhm et al., 2016; Halevy, 2017) or when the out-group 483
showed harmful aggression beforehand (i.e., ex post retaliation of out-group harm; Böhm et 484
al., 2016; De Dreu et al., 2016; Halevy et al., 2010). 485
4. Measures of Intergroup Conflict and Discrimination 486
As section 3 has shown, psychological explanations of individuals’ willingness to engage in 487
intergroup discrimination and conflict vary considerably. Unsurprisingly, the methods, in 488
particular the dependent measures, used in psychological (laboratory) research to assess 489
intergroup prejudice and discrimination are manifold as well. In this section, we review the 490
most established measures. We distinguish three classes: (1) rating measures, (2) behavioral 491
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 22 of 50
measures, and (3) allocation tasks, including first- and third-party allocation tasks, intergroup 492
allocation tasks, and team games as subcategories. 493
4.1 Rating Measures 494
Rating measures are questionnaire-based self-reports, e.g., participants’ agreement or 495
disagreement with certain statements or their attribution of certain characteristics to in-group 496
vs. out-group members. A prominent self-report measure is evaluative or adjective rating. 497
Here, participants are asked to evaluate an in-group (vs. an out-group) member on certain 498
positive and negative value-laden adjectives (e.g., friendly, open-hearted, nasty, egoistic) on 499
n-point scales. Such positive and negative in-group and out-group member evaluations can 500
then be combined into an overall measure of intergroup bias. Applying such an evaluative 501
measurement approach, it is usually found that unknown in-group members are rated more 502
positively than unknown out-group members, merely based on their group membership (for 503
an overview, see Diehl, 1990). 504
Another way of measuring intergroup bias is via participants’ preferred descriptions of 505
in-group and out-group members behaviors (Maas et al., 1989). Here, participants are asked 506
to select among several descriptions of desirable vs. undesirable behaviors shown by in-group 507
vs. out-group members. The descriptions to choose from vary in their level of abstraction, for 508
example, with descriptive action verbs indicating a lower level of abstraction (e.g., ‘The out-509
group member is helping to carry the bag.’) and with adjectives indicating a higher level of 510
abstraction (e.g., ‘The in-group member is helpful.’). The assumption underlying this 511
measurement approach is that rather abstract descriptions are more likely to be taken to 512
describe properties of a person (rather than of a situation; Semin and Fiedler, 1988). 513
Intergroup bias (the so-called ‘linguistic intergroup bias’) can then be observed, when in-514
group members engaging in desirable behaviors and out-group members engaging in 515
undesirable behaviors are preferably described using a high level of linguistic abstraction, 516
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 23 of 50
whereas the opposite is true for in-group (out-group) members engaging in undesirable 517
(desirable) behaviors (as in the examples given above). 518
There are also a number of rather indirect measures, assessing intergroup bias via 519
response latency procedures (e.g., the ‘implicit association task’ and its variants, e.g., 520
Greenwald et al., 1998).8 These kinds of measures try to assess evaluations of in- and out-521
groups of which the participant is largely unaware and hence, whose expression is assumed to 522
lie beyond conscious control (for an overview, see Hewstone et al., 2002). While such 523
measures may be particularly useful if explicit expressions of intergroup bias are likely to be 524
intentionally inhibited due to social desirability (see e.g., Devine et al., 2001), their validity 525
and reliability as well as their predictive power are subject to ongoing debate (e.g., Gawronski 526
et al., 2007; Gawronski and Payne, 2010). 527
4.2 Behavioral Measures 528
The literature also contains several creative (although sometimes deceptive) behavioral 529
measures that can be used to examine specific aspects of prejudice and discrimination. We 530
highlight only two prominent examples. 531
Milgram (1965) devised the so-called ‘lost letter-technique’ to examine prejudice 532
toward out-groups (e.g., Hellmann et al., 2015; Weiner and Lurey, 1973). Milgram dispersed 533
letters with varying addressees like medical institutions, friends of the Communist party or 534
friends of the Nazi party. All envelopes were sealed, stamped, and dispersed in public places, 535
e.g., in shops, telephone booths, or under car windscreen wipers. The idea was that the letter 536
return rate by addressee (all letters were actually addressed to the same postal address, namely 537
that of the experimenter himself) is a proxy for the attitudes people have toward the respective 538
groups. And indeed, Milgram found that more letters were sent back if they were addressed to 539
8 Other approaches to assess implicit biases are based, for instance, on memory tasks (e.g., Crisp and Hewstone,
2001) or psychophysiological measures (e.g., Phelps et al., 2000).
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 24 of 50
more reputable groups (e.g., return rate of 72% for letters to the medical institution vs. 25% 540
for letters to the Nazi party). 541
Another behavioral measure of intergroup prejudice rests on the idea that individuals 542
seek contact with in-group members but avoid contact with out-group members (Bogardus, 543
1925). This can be assessed via the physical distance participants prefer to in-group vs. out-544
group members. One possibility to capture such approach/avoidance tendencies in the lab is to 545
measure the individual willingness to take a seat that is closer to (vs. further away from) a 546
member of each group. For instance, Goff et al. (2008) measured how participants would 547
position chairs to have a ‘comfortable conversation’ with other in-group vs. out-group 548
members (for a similar measure, see e.g., Macrae et al., 1994). The physical distance between 549
the chairs then served as an objective measure of prejudice, with a greater distance to the out-550
group compared to the in-group member indicating more prejudice. Goff et al. (2008) indeed 551
found that participants who expected an interaction with an out-group member were more 552
likely to increase physical distance than those who thought they would speak with an in-group 553
member. 554
Behavioral assessments like these two examples measure rather spontaneous intergroup 555
behaviors. However, they are quite domain-specific and often unable to uncover the 556
motivations underlying the observed behaviors. Allocation tasks are able to overcome these 557
limitations to some extent. 558
4.3 Allocation Tasks 559
The measures listed in this subsection examine intergroup behavior through studying the 560
allocation of valuable units (e.g., money) to in-group vs. out-group members. By clearly 561
defining the quantitative consequences of certain allocation choices, these measures can also 562
partially distinguish the underlying motivations (e.g., greed, fear, aggression). The 563
psychological literature on allocation tasks in intergroup settings can be classified into four 564
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 25 of 50
different types: (1) third-party allocations tasks, (2) first-party allocation tasks, (3) intergroup 565
allocation tasks, and (4) team games. 566
4.3.1 Third-Party Allocation Tasks 567
In third-party allocation tasks, the participant is asked to distribute resources between an in-568
group member and an out-group member. Thus, the allocation choice has no consequences for 569
the decision maker’s own outcome but measures the preference for the welfare of in-group vs. 570
out-group members, independent of own welfare. The allocation decision itself can be used as 571
a direct measure of intergroup bias, i.e., the relative amount of units allocated to the in-group 572
vs. the out-group member. The most prominent example are the reward allocation matrices 573
used by Tajfel and colleagues (e.g., Tajfel et al., 1971). Later research, arguing that the 574
structure of these matrices is biased toward finding intergroup bias, refined the matrices 575
accordingly (e.g., Bornstein et al., 1983; Yamagishi et al., 1999). 576
4.3.2 First-Party Allocation Tasks 577
Given that many real-world allocations require the decision maker to bear individual costs in 578
order to benefit or harm others, an individual’s level of prosociality may play an important 579
role in intergroup conflict. Whereas third-party allocation tasks intentionally exclude costs to 580
the decision maker, these costs are considered in first-party allocations. Participants’ 581
willingness to help in-group members and out-group members at a cost to themselves is 582
compared. The relative difference in the two independent allocation decisions serves as a 583
measure of intergroup bias. In principle, the allocation decision can take the form of any two-584
person game. It only requires that the same game is used in interaction with the in-group and 585
out-group member. For instance, intergroup biased allocations have been found using the 586
dictator game (e.g., Ben-Ner et al., 2009), trust game (e.g., Fershtman and Gneezy, 2001), and 587
prisoner’s dilemma game (Goette et al., 2012).9 588
9 As evident from the cited papers, first-party allocation tasks are also popular among economists. One reason
for this might be the interest of behavioral economics in other-regarding/social preferences (for an overview, see
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 26 of 50
4.3.3 Intergroup Allocation Tasks 589
In many intergroup interactions, a group rather than an individual makes decisions about the 590
outcomes for the in-group and out-group, e.g., using a majority rule. In principle, the decision 591
is similar to first-party allocation tasks, except that the group’s joint decision affects all 592
members of the in-group equally (thus, there is no conflict of interest among the in-group 593
members; they form so-called ‘unitary teams’, see Bornstein, 2003). In this setting, it can be 594
studied whether interindividual interactions differ from intergroup interactions under the exact 595
same incentives, e.g., two individuals vs. two groups playing a prisoner’s dilemma game. 596
Research has shown that interactions between groups are usually less cooperative than 597
interactions between individuals in various interaction tasks. This phenomenon has been 598
labeled ‘interindividual-intergroup discontinuity’ (for a meta-analysis, see Wildschut et al., 599
2003). It has been argued that this discontinuity effect may be explained by greater greed 600
and/or fear in intergroup compared to interindividual interactions, or by group decisions being 601
‘more rational’ because group members attain a more thorough understanding of the game 602
structure through the intragroup discussions that often precede the group decision (for an 603
overview of potential explanations, see Wildschut and Insko, 2007). 604
4.3.4 Team Games 605
Intergroup allocations consider only the conflict of interest between groups, while assuming 606
that the interests of in-group members align. In real-world intergroup conflict, however, 607
intergroup discrimination is often costly to the discriminating individual (see section 3.2.6). 608
Therefore, team games model both a conflict between groups and the potentially conflicting 609
interests of members within a group, i.e., a multi-level conflict (for an overview, see 610
Bornstein, 2003). 611
e.g., Fehr and Schmidt, 2006) and how such preferences may potentially differ between in-group and out-group
interaction partners.
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 27 of 50
The intergroup prisoner’s dilemma game (Bornstein, 1992) is a prominent example. In 612
this game, players are divided into two equally sized groups. Group members have to decide 613
individually and independently whether to contribute to a public good that increases the 614
payoff of each in-group member but decreases the payoff of each out-group member. 615
Contributions are costly, such that individual payoff maximization would predict withholding 616
contributions. In addition, withholding contributions maximizes social welfare, i.e., the 617
payoffs of all players, taking both groups together. In contrast, contributing to the public good 618
maximizes the payoffs of in-group members and the relative difference in payoffs between 619
groups. Several adaptations of this game have been devised to distinguish, for instance, 620
between the motivations to benefit the in-group vs. harm the out-group and between the 621
motivations to egoistically maximize personal payoff vs. prosocially maximize collective 622
welfare (Halevy et al., 2008). Other adaptations have been proposed to distinguish between 623
offensive vs. defensive intentions (Böhm et al., 2016; De Dreu et al., 2016). 624
In principle, team games are structurally similar to the contest games studied in 625
economics and biology (Kimbrough et al., in press, this issue; Rusch and Gavrilets, in press, 626
this issue). Using team games, it has been shown that groups are more likely to overcome 627
internal free-riding tendencies if the intragroup conflict is embedded in an intergroup conflict 628
(Bornstein and Ben-Yossef, 1994). Furthermore, the motivation to benefit the in-group 629
appears to be a stronger motivation to engage in costly intergroup conflict than the motivation 630
to outcompete or harm the out-group. In fact, participants often try to avoid actively harming 631
out-groups if possible (e.g., Halevy et al., 2012, 2008; Weisel and Böhm, 2015). 632
5. Disentangling Semantics 633
As the previous sections have shown, psychological theorizing about human perceptions, 634
motivations, and behaviors relevant in the context of intergroup conflict is diverse and relies 635
on a variety of measures. Remarkably, these measures differ in their treatment of the three 636
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 28 of 50
basic types of outcomes that intergroup conflicts can have: those for the target individual, its 637
in-group members, and the out-group members. Accordingly, the intergroup biases they 638
measure are quite different, too (see Table 1). 639
However, psychologists working on intergroup conflict use a substantially overlapping 640
terminology when referring to intergroup bias and typically do not account for these 641
differences in the incentive structures. In our view, this represents one of the most important 642
obstacles to future work in this field – a problem that can be fixed through a refined 643
terminology, though. 644
645
Table 1. Indicators of intergroup bias in different allocation task measures. 646
647
Measure
Actor’s
Individual
Outcome
In-group
Recipients’
Outcome
Out-group
Recipients’
Outcome
Indicator of
Intergroup Bias
Suggested Label of
Intergroup Bias
Third-Party
Allocation
Tasks
n/a
y
z
y > z
Parochialism
First-Party
Allocation
Tasks
x1
y
n/a
(x1 – y) < (x2 – z)
Parochial Altruism,
Composite Measure
x2
n/a
z
Intergroup
Allocation
Tasks
x
x
z
x > z
Parochial Mutualism
Team
Games
x
y
z
(y > x) ⋀ (y > z)
Parochial Altruism,
Direct Measure
Note. x, y, z: marginal outcomes (x + y + z = const.) as a consequence of a actor’s decision; n/a: no effect of
decision on this outcome. In-group recipients’ outcome and out-group recipients’ outcome refer to outcomes of
individual group members.
648
Take ‘parochial altruism’ as an example (see section 3.2.6). The concept was originally 649
coined to explain a very specific phenomenon, namely individually costly but in-group 650
beneficial behavior that harms an out-group, all at the same time. However, over time, this 651
initially quite precise meaning of the term has softened and parochial altruism has become a 652
catch-all term for a variety of intergroup biases (Cacault et al., 2015). As can easily be seen 653
from Table 1, though, behavior that completely fulfils the original definition of parochial 654
altruism is captured only by team games, in which an individual can contribute to in-group 655
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 29 of 50
success at a personal cost (y > x) in order to make the in-group fare better than the out-group 656
(y > z). Although a similar structure is also present in first-party allocation tasks, in these the 657
interest of the in-group and the interest of the out-group never are in direct conflict. Hence, an 658
intergroup bias as measured by a first-party allocation task only represents a composite proxy 659
of parochial altruism. 660
The ‘social semantics’ developed by West and colleagues (West et al., 2007), are 661
helpful in disentangling the other ‘biases’ as well. They distinguish four types of social 662
behaviors based on their outcomes for the acting individual, ‘actor’, and the individual(s) 663
affected by the action, ‘recipients’: Mutually beneficial behavior (+/+) benefits all parties, 664
selfish behavior (+/–) benefits the actor at a cost to the recipients, spiteful behavior (–/–) is 665
costly for all parties, and altruistic behavior (–/+) benefits the recipients at a cost to the actor. 666
Accordingly, the intergroup bias measured with intergroup allocation tasks is best described 667
as ‘parochial mutualism’ because the actor’s outcome is aligned with the in-group recipients’ 668
outcome. In contrast, the intergroup bias measured through third-party allocation tasks should 669
merely be labeled ‘parochialism’, as it does not bring the actor’s self-interest into conflict 670
with the in-group or out-group recipients’ outcome and is thus neither altruistic nor 671
mutualistic. 672
As these examples show, refined terminology can be of great clarificatory use for the 673
interpretation of theoretical and empirical work on individual group-conditional social 674
behaviors. And, at least in our view, this is more than just quibbling, for example because 675
there are important differences between the trajectories along which mutualism and altruism 676
evolve (West et al., 2011), but also because clear conceptual distinctions can help to design 677
behavioral experiments that differentiate between (parochially) altruistic and (parochially) 678
mutualistic motives more clearly. In addition, clarifying the (differential) motivations that can 679
lead to biased intergroup behavior may also help to increase reproducibility of intergroup bias 680
effects. 681
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 30 of 50
It should of course be noted that the refinements just suggested are still coarse. They 682
can be extended to include heterogeneous effects of the actor’s behavior on different in-group 683
and out-group recipients, and, importantly, also behaviors that have negligible costs. 684
Additionally, our suggested semantic differentiation does not distinguish between behaviors 685
that do not benefit out-group members (or to a lesser degree than in-group members) vs. 686
behaviors that harm out-group members. However, this distinction might be a psychologically 687
important one (e.g., Mummendey et al., 2000; Weisel and Böhm, 2015). Accordingly, it has 688
been suggested recently to label the former ‘weak’ parochial altruism, and the latter ‘strong’ 689
parochial altruism (Böhm, 2016; Böhm et al., 2017). Future research is definitely needed, 690
though, to better understand the psychological underpinnings of these qualitatively different 691
forms of discriminatory out-group treatment. 692
6. Epilogue: De-Biasing Intergroup Perceptions 693
Psychological research has proposed various interventions to de-bias intergroup perceptions 694
in order to avoid or reduce intergroup conflict. These interventions rest on different 695
assumptions about the underlying processes and causes of intergroup conflict as proposed by 696
different theories (see section 3.2). As we cannot describe all these interventions in detail, we 697
provide selected examples in the following. 698
6.1 Changing Incentives 699
According to realistic group conflict theory (see section 3.2.2), groups’ negative 700
interdependence over scarce resources creates intergroup conflict. Consequently, decreasing 701
negative outcome interdependence and increasing positive outcome interdependence should 702
reduce intergroup conflict. Indeed, it has been shown that ‘doing things together’ to achieve 703
shared outcomes can increase intergroup cooperation and liking (Sherif, 1958). 704
6.2 Changing Social Categorizations and Out-Group Perceptions 705
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 31 of 50
Social identity theory (see section 3.2.3) posits that intergroup conflict may arise even in the 706
absence of negative interdependences between groups as a result of social categorization 707
processes. Interventions derived from this perspective aim to change individuals’ level of 708
categorization (for an overview, see e.g., Hewstone et al., 2002). First, ‘decategorization’ 709
seeks to eliminate social categorization through dissolving the perception that opposing 710
groups form homogeneous units (‘differentiation’ and ‘personalization’). Supporting the 711
effectiveness of this strategy, it has been shown that an interpersonal focus decreases 712
intergroup bias (e.g., Bettencourt et al., 1992). Second, ‘recategorization’ seeks to change the 713
level of categorization from ‘us’ vs. ‘them’ (i.e., salience of subordinate social identities) into 714
‘we’ (i.e., salience of the superordinate level of categorization). There is evidence that such a 715
higher level of categorization reduces intergroup bias over time (e.g., Dovidio et al., 1995; 716
Gaertner et al., 1990). 717
Although both decategorization and recategorization can reduce biased intergroup 718
perceptions and behaviors, eradicating or replacing original categorizations may not always 719
be possible or could threaten individuals’ need for assimilation and differentiation (Hewstone 720
et al., 2002). Therefore, other approaches aim to reduce intergroup conflict while maintaining 721
the individuals (different) social identities. A prominent intervention of this kind is intergroup 722
contact (for an overview, see Pettigrew, 1998). Following Allport’s (1954) original 723
formulation, it has been suggested that interpersonal contact between members from different 724
groups can improve attitudes toward out-groups given that (i) individuals perceive to have 725
equal status, (ii) the contact situation encourages cooperation and promotes common goals, 726
(iii) has normative and institutional support, and (iv) allows for the development of friendship 727
through repeated and meaningful interaction; ideally, then, positive experiences made with 728
individual out-group members generalize to a more positive attitude toward the out-group as a 729
whole. 730
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 32 of 50
Meta-analytical evidence indeed found that intergroup contact reduces intergroup bias 731
by enhancing knowledge about the out-group, reducing anxiety about intergroup contact, and 732
increasing empathy and perspective taking (for meta-analyses, see Pettigrew and Tropp, 2008, 733
2006). Hence, among other things, intergroup contact can reduce perceived out-group threat 734
(see section 3.2.4). More indirect forms of intergroup contact have also been shown to 735
decrease intergroup bias (for a review, see Dovidio et al., 2011), e.g., observing an in-group 736
member experiencing positive intergroup contact (Mazziotta et al., 2011), or even just 737
imagining a positive intergroup interaction (e.g., Crisp et al., 2009). 738
Other interventions focus on increasing the salience of shared group memberships. For 739
instance, two individuals from different working teams may be fans of the same sports team 740
or may have graduated from the same school. Highlighting such overlapping group 741
memberships has also been shown to reduce intergroup bias (e.g., Crisp et al., 2006; Crisp and 742
Hewstone, 1999). 743
6.3 Changing Perceptions of Mutual/Opposing Interests 744
The theory of bounded generalized reciprocity (see section 3.2.5) assumes that individuals are 745
prone to perceive aligned interests with in-group members and, in turn, to readily engage in 746
costly in-group cooperation, while avoiding cooperation with or even actively harming out-747
group members. Some theories even suggest that such ‘default’ perceptions and preferences 748
may have been shaped by evolutionary adaptation processes (see section 3.2.6). Yet, there are 749
several interventions that aim to reduce intergroup bias by reshaping individuals’ cognitive 750
representations of how their personal interests relate to those of in-group and out-group 751
members. We describe four of such interventions. 752
First, intergroup bias is supported by the ‘illusion of morality as self-interest’ (Baron, 753
2012, 2001, 1997). People tend to think that individually costly contributions that benefit their 754
group are actually in their self-interest. They reason, “What I contribute helps my group. I am 755
a member of my group. Therefore, my contribution helps me.” However, this reasoning 756
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 33 of 50
neglects the fact that in many cases their personal return is actually lower than their 757
contribution. This illusion is larger when the group is easily identified as the individual’s in-758
group (Baron, 2012, 2001). However, when group members are forced to calculate the self-759
interest benefit of their contribution, along with its benefit for others, both the self-interest 760
illusion and in-group bias itself are reduced. 761
Second, intergroup bias is greater when outsiders are thought of as a group rather than 762
as individuals (Baron, 2012). It has been shown that supposing that out-group harm would 763
occur to an identified individual (even if identified by just a name) would reduce the 764
willingness to support such harm. In one experiment (Baron, 2012), for instance, participants 765
made hypothetical decisions about proceeds from investments of funds contributed by 766
workers in a company with offices in different countries. American participants were more 767
intergroup biased when the ‘other office’ was in China or India than when it was in the U.S. 768
Importantly, this effect was greater when they voted on decisions about entire offices than 769
when they made decisions about themselves and a single co-worker in another office. These 770
results suggest that intergroup bias is associated with abstract representations of groups rather 771
than direct experience of individual human beings. Thus, intergroup bias might be 772
ameliorated by focusing on the humanity of individual out-group members. 773
Third, intergroup bias is greater when the option that helps the in-group but hurts the 774
out-group is an omission than when it is an act (e.g., Baron, 2012; Weisel and Böhm, 2015). 775
In general, people evaluate harmful acts as morally worse than equally harmful omissions. 776
They are willing to let out-group members suffer harm by failing to help them, in order to 777
help their in-group. But they are much less willing to take an action that hurts out-group 778
members to the same extent, for the same in-group benefit. Thus, reframing harmful 779
omissions as if they were actions, e.g., opposing a reform, or failing to oppose a regression in 780
policy, can increase people’s inclination to think about the out-group harm they would cause. 781
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 34 of 50
Fourth, intergroup bias is supported by beliefs about the moral duty of in-group 782
members toward one another (e.g., Baron, 2012; Baron et al., 2013; Buchan et al., 2009). 783
These findings suggest that many individuals are not parochial but are, in their value 784
judgments, truly cosmopolitan. Still, they show intergroup bias because they accept certain 785
malleable cultural norms about what our duties are. Challenging such cultural norms, for 786
instance, by demanding justification, could therefore reduce intergroup bias (Singer, 1981). 787
7. Discussion and Outlook 788
To summarize: Research on psychological mechanisms underlying potentially conflictual 789
intergroup relations is a rich field consisting of partially complementary, partially competing 790
theories, working with a plethora of rating instruments as well as observational and allocation 791
(game) measures (see Table 2 for a synoptic overview). Still, an undisputed assumption at the 792
intersection of all theories, and a core insight of virtually all empirical work on the topic, is 793
that humans readily condition their attitudes and behaviors on markers of group membership. 794
Yet, our understanding for why this is so diverge and the list of personality traits and 795
situational factors that can turn co-existing groups into enemies still is tentative and partially 796
disputed. 797
798
Table 2. Research on intergroup conflict in psychology. 799
800
Description
A formal definition of intergroup
conflict
The perceived incompatibility of goals or values between two or more
individuals, which emerges because the involved individuals classify
themselves as members of different social groups.
Important theories of intergroup
conflict
Personality theories, e.g., right-wing authoritarianism (e.g., Altemeyer,
1998); social dominance orientation (e.g., Sidanius and Pratto, 2001)
Realistic group conflict theory (Sherif, 1966)
Social identity theory (Tajfel and Turner, 1986, 1979)
Integrated threat theory (Stephan and Stephan, 2000)
Theory of bounded generalized reciprocity (Yamagishi et al., 1999)
Theory of parochial altruism (Choi and Bowles, 2007)
Methods used to study intergroup
conflict
Primarily experiments using different measures of intergroup prejudice
and discrimination, e.g., rating measures, behavioral measures, allocation
tasks (third-party, first-party, and intergroup allocations, team games)
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 35 of 50
801
Given the complexity of the matter and the partially incompatible views of the workings 802
of human psychology on which some of the theories presented above are based (e.g., 803
culturalistic vs. naturalistic), we hold that an all-embracing convergence on ‘the’ 804
psychological theory of intergroup relations is not to be expected soon, if ever. However, we 805
do think (i) that a unified semantic framework would be of great help in moving this field of 806
research forward (see section 5); (ii) that, given the plethora of existing empirical work in this 807
field, the time is ripe for intensified meta-analytical work (e.g., Aberson et al., 2000; Balliet et 808
al., 2014; Bettencourt et al., 2001; Riek et al., 2006); and (iii) that studies that compare the 809
robustness of previously reported effects across different measurement methods are a very 810
important next step (see section 4). Moreover, we see a great potential for future research in 811
psychology (iv) that integrates theories and methods from other scientific disciplines. For 812
instance, anthropological and biological research may help psychologists to identify important 813
modulators of individual behaviors in intergroup conflict, e.g., intra- and intergroup 814
heterogeneity in status, power, or incentives (e.g., Gavrilets and Fortunato, 2014; Glowacki et 815
al., 2016). Research in economics and management could support psychologists in devising 816
novel and more fine-grained behavioral (game) measures of intergroup discrimination (for an 817
overview, see Kimbrough et al., in press, this issue). Moreover, bio-physiological methods 818
(e.g., neuro-imaging, hormone-level tracking) may serve as an additional tool to further 819
explore and understand the psychological processes involved in intergroup conflict (e.g., 820
Cikara and Van Bavel, 2014; De Dreu et al., 2011). We believe that the synergies as well as 821
the frictions that such exchanges of theoretical views and methodological approaches produce 822
will certainly yield stimulating impulses for the advancement of the field(s). 823
All in all, we are optimistic that the psychological study of intergroup conflict will 824
blossom forth in the nearer future, in particular because ending ongoing intergroup conflicts 825
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 36 of 50
and preventing new ones from escalating remains one of the most pressing problems of the 826
century (Fiske, 2002). 827
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 37 of 50
Acknowledgements 828
We are grateful to Kevin Laughren for conducting the literature search underlying Figure 1. 829
THE PSYCHOLOGY OF INTERGROUP CONFLICT Page 38 of 50
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