Development and Trends of Intergroup Contact Studies

Intergroup contact is considered as an effective intervention strategy to reduce intergroup bias, increase intergroup trust, and promote inter-group relationships. The study used CiteSpace software to do a visual analysis on the 2966 articles from the Web of Science Core Collection database between 2012 and 2022. It was found that during this period, the number of articles focus on intergroup contact increased steadily year by year, with social psychology as the main discipline background, the researchers are mainly conducted in the United States and the research content focused on intergroup contact theory, intergroup attitude, intergroup anxiety, reducing bias and other topics. Moreover, it formed the foundation of knowledge including direct contact and indirect contact, mechanism of how intergroup contact to improve intergroup bias, and intergroup contact intervention strategies. Research trends mainly include positive contact, negative contact, and social change research.


Introduction
In order to solve the problems of national unity and ethnic conflict after the world war, western social psychologists have developed a set of theoretical system focusing on how intergroup communication affect inter-group relations after continuous research, which has been widely recognized and gradually become one of the most effective strategies to improve intergroup relations. In 1954, the publishing of the American social psychologist Allport's classic book The Nature of prejudice was regarded as a sign of the formation of intergroup contact theory. He believes that contact under the four best conditions, including status equality, common goals, cooperation, and authority (institutional, customs) support, can generally reduce intergroup bias and thus enhance positive intergroup relations. After Allport proposed the contact hypothesis, a large number of studies have confirmed that intergroup contact can indeed reduce intergroup bias. At present, there are both domestic and foreign researchers which have reviewed the field of intergroup contact from different perspectives. For example, Yaming (2015) reviewed the research progress of the western intergroup contact theory from four aspects: the effectiveness of the intergroup contact, the optimal conditions, the action mechanism and the facing difficulties. Jing and Bin ( 2004 ) commented on Allport's contact hypothesis, others' doubts about the contact hypothesis, and the intergroup contact theory model proposed by Pettigrew. Dovidio et al(2003)have reviewed the development history of the contact hypothesis, introducing recent developments in the field and future research directions. However, these reviews mainly summarize and generalize the existing research knowledge, rather than exploring the status of intergroup contact research by metrology method. Therefore, it is necessary to summarize the research status in the field of intergroup contact abroad, and sort out the research status, hot spots and trends in this field to provide reference for follow-up research.

Data Collection and Research Tools
The data of the article were collected from the Web of Science (WOS) core collection database, and used intergroup contact as the search topic. The literature search time span was set to be between 2012-2022, literature type was selected as Article. There are a total of 2,966 literature articles were retrieved, data retrieval and download date is May 24, 2022 (The data of 2022 is set for the months before June). The study used Microsoft Excel software, CiteSpace5.8 software, and analytical retrieval tools from the WoS platform to analyze the data, so that researchers can intuitively understand the current research hotspot of intergroup contact, the basic research knowledge and other information.

Data Analysis
Research Status Analysis 1. Analysis of the number of published papers Generally speaking, the annual number of published papers is considered as one of the important indicators to evaluate the development status and trend of a certain research field. From the distribution of the literature, from 2012 to 2022, the research literature on intergroup contact generally showed a steady upward trend. This shows that the field of intergroup contact has received general attention from researchers (see Figure 1). In 2012-2022, the countries with the most studies of intergroup contact were the United States, the United Kingdom, the Netherlands, Germany, Australia, and Canada. These countries are all countries of immigrants, and the group relationship between immigrants and local residents has always been an issue of the government. Among them, the number of studies in the United States reached 1156, accounting for about 38.9% (see Figure 2).

Distribution of Disciplines
In 2012 -2022, the study of intergroup contact involved multiple disciplines. It mainly includes psychology, sociology, social science and other topics, pedagogy, government law, etc. It reflects the multidisciplinary and interdisciplinary research perspective of this research field. Among them, there are up to 1,857 articles have discussed the number of intergroup contact problems from a psychological perspective, accounting for about 62.6% (see Table 1). Cooperative Author Analysis Set Time Slicing from 2012 to 2022, with 3 years as a time slice, set the node types as Author and select Thresholds in the selection criteria column, then formed the intergroup contact cooperative author network map. A node in the figure represents an author, and the node size represents the number of authors, the larger the nodes, the greater number of posts. The thickness of the connection between the nodes is positively correlated with the strength of the author cooperation. The distribution of research co-authors in the field of intergroup contact is "overall centralized and partially dispersed". From the view of intensity of cooperation, the close cooperation is the four research teams with Miles Hewstone, Loris Vezzali, Maykel Verkuyten, Sofia Stathi as the core. The largest node in the map is the Miles Hewstone research team at the core, with 80 posts (see Figure 3). Among them, Hewstone is the director of the Oxford Centre for Intergroup Conflicts Studies at the Department of Experimental Psychology, Oxford University and a member of the British Academy of Sciences. His research mainly focuses on prejudice, stereotypes, intergroup contact, intergroup conflict, and racial segregation and integration.

Knowledge Base Analysis
The knowledge base of group-to-group contact research field with high co-citation frequency are considered to be the key node literature that have made major theoretical innovations in the research field and are most likely to form the frontier hotspot in the research field (see Table 2).

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As can be seen from Table 2, the total citation frequency of these five documents is relatively high, which lays a good knowledge foundation for the development of the field of intergroup contact research. Among them, the total frequency of citation ranked the first is Pettigrew and Tropp's, A Meta-Analytic Test of Intergroup Contact Theory which was published in Journal of Personality and Social Psychology in 2006.The authors analyzed 515 studies (n=250089) from 38 countries, and the results show that intergroup contact does reduce intergroup bias, and that this contact effect can be extended to outgroup members. At the same time, the study also demonstrated that the optimal contact condition of Allport is not necessary to produce a positive intergroup contact effect, and that the study's characteristics and the participants' characteristics (such as the study environment, participants' age and gender, and the group type related to contact) are also important regulatory variables of the intergroup contact effect.
In second place is Pettigrew and Tropp's, How does intergroup contact reduce prejudice? Meta-analytic tests of three mediators which published in European Journal of Social Psychology in 2008. The literature focuses on the mediation effect of several variables in the process of intergroup contact reduction bias, such as outgroup understanding, intergroup anxiety, and empathy (opinion selection). The results show that emotional factors (decreased anxiety and increased empathy) are the main mediating variables of intergroup contact effects, compared with the cognitive factor like understanding of outgroups.
In third place is Davie, Tropp and Pettigrew's, Cross-Group Friendships and Intergroup Attitudes: A Meta-Analytic Review. The paper published in Personality and Social Psychology Review in 2011. This study identifies how cross-group friendships are conceptualized and measured in intergroup research, investigates which operationalizations yield the strongest effects on intergroup attitudes, explores potential moderators, and discusses the theoretical importance of the findings. Prior meta-analyses have provided initial evidence that crossgroup friendships are especially powerful forms of intergroup contact.  Barlow, FK and Paolini, S.The results of the study extend the contact hypothesis by issuing an important caveat: Negative contact may be more strongly associated with increased racism and discrimination than positive contact is with its reduction.

Research Hotspots and Frontier Analysis 1. Research Hotspot Analysis
The hotspots of intergroup contact research can be summarized by keyword co-occurrence analysis in bibliometrics. The study used CiteSpace software to analyze data and count high frequency keywords in inter-group contact study (see Table 3). By analyzing the data in Table  3, the intergroup contact research hotspots had the following characteristics between 2012 and 2022. First, social psychology is taken as the main discipline perspective. The highfrequency keywords such as attitude, prejudice, social identity and intergroup relation appear in Table 3, which all belong to the research direction under the branch of social psychology. Therefore, intergroup contact has attracted wide attention from social psychology researchers. Second, the special population is taken as the main research subjects. Highfrequency keywords such as minority groups, immigrant, northern ireland and gay men appear in Table 3. Third, Focused on the theoretical research of intergroup contact. In terms of theoretical research, key words such as intergroup contact theory, contact hypothesis and social dominance orientation appear in Table 3.

Research Frontier Analysis
In bibliometrics, emergent words refer to keywords that suddenly increase in frequency over a certain period of time, the higher the sudden intensity keyword, the more it represents the frontier of the research field. Using the CiteSpace software operation to find the top 25 protruding words. Analysis of these sudden occurrence words found that the key words like interracial friendship, positive contact, prosocial behavior, reducing prejudice, social interaction, interracial interaction, perceived group threat have become the frontier of intergroup contact research.

Discussion Current Status of Intergroup Contact Research
Since 2008, the number of articles published in the field of intergroup contact research has shown a steady upward trend. Research in this field is mainly in the United States and focus on social psychology. This may be related to the intergroup contact theory was proposed by social psychologists in the United States. Since 1947, when Cornell University social psychologist Williams first systematically expounded the "intergroup contact theory" in his monograph The Reduction of Intergroup Tension, researchers began to rigorously verify this theory. In 1954, Allport, an American social psychologist, as the master of the field of intergroup contact research, discussed the intergroup contact theory in detail in his classic book The Nature of Prejudice, and proposed the contact hypothesis. Most of the subsequent studies on intergroup contact based the contact hypothesis proposed by Allport. At the same time, in the face of social problems such as racial segregation, racial prejudice, and racial conflict, positive intergroup contact is considered to be effective in reducing intergroup bias or intergroup conflict, increasing intergroup trust, or intergroup forgiveness, so as to establish a harmonious intergroup relation.

Knowledge base for Inter-Group Contact Research
The knowledge base of research in this field can be summarized from the intergroup contact high-frequency co-citation literature in the past 10 years. It mainly includes three aspects: type of intergroup contact, psychological mechanism of intergroup contact improving intergroup bias, and intergroup contact with intervention strategies.

Direct Intergroup Contact and Indirect Intergroup Contact
According to the early intergroup contact hypothesis, the intergroup bias is due to the lack of sufficient information or misinformation about another group, and the direct contact provides the opportunity for both sides to obtain new information and clarify the misperception. After extensive experimental research, it is found that the direct intergroup contact under the four best conditions of equal status, common goals, cooperation, and authority support can reduce the bias of external groups. However, in real life, there is often a lack of conditions or opportunities for direct contact between groups, such as unequal status, lack of common goals, and various kinds of. Therefore, some researchers have examined the indirect intergroup contacts and their effects. Indirect intergroup contact is a non-face-to-face form of intergroup contact that mainly includes extended contact, imaginative contact and vicarious contact. Extended contact effect refers to the fact that if the individual learns of the friendship relationship between the inner group members and the outgroup members, it can effectively reduce the bias of the outgroup, so as to improve the attitude of the outgroup. The imaginative intergroup contact hypothesis suggests that psychologically simulating positive interactions with outgroup members can improve intergroup attitudes, increase intergroup trust, and reduce intergroup bias, and promote positive group relationships. Vicarious intergroup contact is the process by which individuals can interact successfully with the outgroup members by observing the outgroup members, thereby improving attitudes towards the outgroup. With the advent of the Internet age, the contact in the virtual society has become a part of people's daily life. Some researchers have therefore proposed a new vicarious intergroup contact which is the internet contact. Through summary analysis, some researchers believe that indirect intergroup contact can effectively reduce people's bias towards outgroups. Therefore, either direct or indirect intergroup contact can effectively reduce intergroup bias and thus improve intergroup attitudes.

Mechanism of Intergroup Contact in Improving Intergroup Bias
After confirming that intergroup contact can indeed reduce intergroup bias, researchers are generally concerned about the specific mechanism of intergroup contact in improving intergroup bias. To answer this question, the researchers not only examined objective factors such as the study situation, group type and contact conditions, but also considered subjective factors such as empathy, understanding of external groups and intergroup anxiety, and further explored the mediation variables and regulatory variables affecting the intergroup contact effect. For example, Pettigrew and Tropp (2008) pointed out in their research that contact conditions, research and subject characteristics are important regulatory variables in the "contact-bias" effect, while outgroup understanding, intergroup anxiety, and empathy / opinion selection play an important mediating role in the process of "intergroup contact reduction bias". Turner et al (2008) suggested that extending intergroup exposure reduces intergroup bias by intergroup anxiety, perception of internal and outgroup rules, and the mediation of incorporating outgroup into self-moderate variables. Voci and Hewstone (2016) examined the mediation of anxiety and the modulation of group significance in a survey of the effects of contact among groups of Italian immigrants. Mazziotta et al (2011) argued that the relationship between alternative contacts and intergroup attitudes is successively modulated by self-efficacy expectations and intergroup perceived uncertainty.

Intergroup Contact served as a Practice Intervention Strategy
Intergroup contact has been widely recognized as an effective intervention strategy to improve intergroup attitudes and promote inter-group relationships. It has been suggested that direct intergroup contact may be a key factor in reducing the impact of AIDS-related stigma on contaminated groups, and the combination of expert lectures and direct contact can effectively reduce the stigma of mental illness. In a real-world situation, there are few opportunities for direct contact between groups or the positive contact conditions are difficult to meet, so the researchers also examined the intervention effect of indirect contact. Some researchers believe that the degree of imaginative exposure promoting willingness to promote intergroup contact is greater than improving intergroup attitudes. Vicarious exposure could both increase participants' willingness to participate in direct cross-group exposure and improve participants' attitudes to outgroup members. It can be seen that different intergroup contact types have different advantages in enhancing intergroup relationships. However, at present, researchers mainly investigate the single intergroup contact effect, and lack to study the effect of different intergroup contact types to improve intergroup attitudes from a comprehensive perspective. Some researchers suggest that in the social intervention, the imaginative contact intervention can be adopted in the early stage, followed by the extended contact. When people are aware of the permeability of group boundaries, they re-create face-to-face contact, which can reduce inter-group anxiety and achieve the optimal inter-group contact effect.

Research Hotspots and Frontiers of Intergroup Contact 1. Research hotspots of intergroup contact
At present, the research topics of intergroup contact mainly include positive attitude, intergroup anxiety, negative attitude, positive contact, outgroup members, ethnic differences, minority groups, bias reduction, contact theory, mediation role, etc. The initial aim of the intergroup exposure study was to examine how to reduce racial or ethnic bias. With the deepening of the research, the researchers found that the intergroup contact not only had an effect on the research participants, but also this contact effect can also be extended to the outgroup members.
Since the American social psychologist Allport proposed the contact hypothesis in 1954, the researchers have adopted experimental research (mainly quasi-experimental research), longitudinal research, meta-analysis, questionnaire survey and other methods to conduct a large number of empirical studies on the relationship between inter-group contact and group attitude and the mechanism of action. Therefore, the key words such as control group, mediation role, and structural equation model emerge. We can explore the relationship between intergroup contact and intergroup attitudes by constructing a structural equation model. By examining the mediation variables and regulatory variables, we can understand the action mechanism of intergroup contact and intergroup attitude, which provides a reference for subsequent researchers to carry out intervention research on intergroup attitudes, such as intergroup bias, intergroup trust, and intergroup forgiveness.

Research Frontiers of Intergroup Contact
Through the keyword co-occurrence analysis, the emerging words representing the research frontier in the field of inter-group contact can be found, mainly including social change, positive contact and negative contact. In recent years, along with social changes and economic globalization, the contact between people, between groups and groups, between various races or nationalities, and between various countries has become increasingly frequent. Such contact may be either positive or negative, and positive contact can effectively promote positive attitudes among groups, while negative contact often triggers negative attitudes between groups. Therefore, social change, positive contact and negative contact have attracted the attention of researchers.

Conclusion
This article uses CiteSpace software to visually analyze 2966 documents themed on intergroup contact from 2012 to 2022 in the WoS core collection, and presents the number of publications in the field of intergroup contact, co-authors, research hotspots and research frontiers in the form of knowledge graph. We can draw the following conclusions.
First of all, in the past 10 years, the annual number of intergroup contact research articles published has been steadily increasing, and it is concentrated in the United States, and mainly in the field of social psychology research. The cooperative distribution of the authors presents the characteristics of "overall concentration and partial dispersion". It has mainly formed four scientific research teams with Miles Hewstone, Loris Vezzali, Maykel Verkuyten, Sofia Stathi as the core. Secondly, the knowledge base in the field of intergroup contact research includes three aspects: direct contact and indirect contact, the mechanism of action of intergroup contact to improve intergroup bias, and intergroup contact as a practical intervention strategy. Finally, the research hotspots of intergroup contact include positive attitude, intergroup anxiety, negative attitude, positive contact, outgroup members, and research frontiers include social change, positive contact and negative contact.
Overall, the intergroup contact theory is believed to play its role in actively promoting the intergroup relations based on the four optimal contact conditions, however, explorations in terms of strengthening the contact effect yet to be explored depending on the context that it will be used.