Background

According to the International Organization for Migration (IOM), an international migrant is a person who moves away from his or her country and crosses international political borders for a variety of reasons [1]. The IOM estimated that there were 281 million international migrants globally in 2020, representing a 3.5% increase from the estimated number of international migrants in 2019 [2]. Not all international migrants have formal authorization to cross international borders. People who cross international borders in ways other than the usual ones or lack formal authorization are called irregular, undocumented, illegal, or unauthorized migrants [1]. People opt for risky journeys to cross international borders without official authorization due to the limited availability of legal migration routes and authorizations. According to the International Centre for Migration Policy Development, almost 200,000 illegal crossings were recorded at European Union (EU) borders in 2021 [3]. Laws and policies regarding crossing international borders have led to criminalization and inhumane practices toward unauthorized migrants, such as long detention periods for reasons related to security checks [4].

Different countries have different border control strategies and different migration policies. In many countries, unauthorized migrants are held in administrative detention centers until official decisions are issued regarding their status, ranging from granting international protection to deportation and the issuing of entry bans. Detention is defined as “a restriction on freedom of movement through confinement that is ordered by an administrative or judicial authority. In many countries, “administrative detention” is part of migration management procedures to ensure that other administrative measures, such as deportation or expulsion, can be implemented” [2, 5]. Several countries have criminalized illegal migrants and, therefore, detained them in special detention centers, even though international law clearly states that detention should only be used as a last resort and never for children. Crimmigration” is a term coined to describe the intersection of criminal law and immigration law. The term has been increasingly used in academic and policy circles to describe the trend of blurring the lines between criminal and immigration law enforcement. Crimmigration policies, such as deportation for noncitizens with criminal convictions, have resulted in the criminalization of immigration violations and the deportation of noncitizens with little or no criminal history [6]. Cimmigration has been fueled by anti-migration activists, certain politicians, and the media that consider migration as a problem and a threat to the culture. Therefore, the mistreatment of migrants in detention centers remains within the walls of detention centers [7].

Migration detention centers exist in many destination countries, such as the US, UK, Australia, and Canada. Little is known about what happens inside these detention centers. However, there were alarming stories about the mistreatment of the detainees inside these centers. A recent report by the World Health Organization (WHO) stated that immigration detention is harmful to health and that an alternative to detention should be used [8]. Migration detention can have a severe psychological impact on the detainees during and after release from detention facilities [9]. Alternatives to detention (ATD) are non-custodial practices used in the context of migration to ensure that people are not detained because of their migration status [1]. Migration detention is widely practiced in the European Union and the United States (US), even though international law states that migration detention should only be used as a last resort and never for children [10]. Therefore, the detention of migrants must conform to international guidelines. However, several headlines on immigration detention in the past few years were disturbing. Examples of such news included Australia’s “Pacific Solution” of offshore detention centers, the separation of Mexican migrant children under US President Trump’s “zero tolerance,” and the EU hotspots in Lampedusa or Greece, which hold asylum seekers on islands for long periods in inhumane conditions [11]. In 2020, the UNHCR published the final report on the Global Strategy Beyond Detention 2014–2019 that aimed to “end the detention of children, to ensure that alternatives to detention (ATDs) are available and to ensure that conditions of detention meet international standards” [12].

A certain number of migrants, such as those with criminal records, visa violations, or those with a suspicious history, are denied entry and citizenship of the destination country and forcibly deported back to their home country. Deportation is defined as the forcible removal of non-citizens due to their illegal entry into the country [1]. Researchers have documented the short- and long-term effects of deportation on children and family members of the deportees [13]. The deportation of migrants and asylum seekers has drawn a lot of legal and emotional debate. For example, the policy of the United Kingdom government to deport asylum seekers and migrants to Rwanda has received a lot of criticism [14]. Certain governments introduced deportation policies to decrease the mass fear and panic in the general public secondary to the media coverage and tweets by certain politicians about the national threat of international migrants [15]. Research on the detention and deportation of migrants, asylum seekers, and other types of migrants is essential for people in the field of migration. Research in this field will contribute to scholarship and knowledge in migration, international human rights, international law, politics, economics, psychology, and demography. Research activity on detention and deportation will positively contribute to the global debate affecting migration policies and international treaties. Human rights advocacy groups, political parties promoting liberal democracies, and experts in international law in the era of globalization and liberalization can use research material as a reference for building policies and guidelines [16]. However, the research trends and patterns on the detention and deportation of migrants are unknown and have not been discussed in the literature. Therefore, it will be useful for the academic and scientific communities, practitioners, and policymakers to know the evolution and structure of knowledge of these related topics in international migration. Bibliometric analysis can assist in identifying research evolution, gaps, collaborative networks, and expected future research trends in a particular field [17]. Bibliometric methods are not new [18]. Bibliometric methodology gained popularity with the development of online databases such as Web of Science and SciVerse Scopus [19]. Different bibliometric studies have evolved over the past few decades [20]. In relational bibliometric studies, the relationships between units in research articles such as authors, journal name, keywords, author affiliation, and references, were examined to allow assessment of the intellectual, social, and knowledge structure of a particular research area [21]. Based on this, the objectives of the current study were to assess the (1) evolution; (2) knowledge structure; and (3) potential future research on the detention and deportation of migrants using bibliometric methodology.

Methods

Database

In the current study, data were collected from the Scopus database. Scopus was selected to achieve the objective of the present study for several reasons. First, Scopus is the largest scientific database relative to other databases such as Web of Science. Second, the ease of data export, analysis, and compatibility with Microsoft Excel and visualization programs. Third, Scopus is a general database with citations in all fields, including social and health disciplines. This is important because research in the field of detention and deportation falls within different scientific disciplines. Therefore, Scopus was the most suitable for the current study [22].

Search Strategy

Research articles on the detention and deportation of migrants published between 1900 and December 31st, 2022, were retrieved. Various Boolean operators (OR, AND, AND NOT) available in the Scopus search function were used. The terms and strings used to develop the search strategy were obtained after reviewing various studies on the topic [9, 23, 24]. Scopus allows the use of asterisks and quotation marks to sharpen and broaden the search strategy. Table 1 summarizes the search strategy, including the search strings, inclusion and exclusion criteria, and the number of results at each step. The search strategy was limited to the study period from 1900 to December 31st, 2022. Not all retrieved documents were considered for the analysis. Only journal research and review articles were included in the analysis. The study did not consider other types of documents such as books, book chapters, editorials, notes, conference papers, and errata.

Table 1 Search strategy for retrieving documents on detention and deportation of migrants (1900–2022)
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Validation

The accuracy of the search strategy and the absence of bias were confirmed by reviewing the titles and abstracts of the top 100 cited articles in the retrieved dataset by two volunteers (S. Z. and A. A.). Based on the review process, a list of terms was added to the search query as an exclusion step. For example, certain documents about non-human migration or cell/macrophage migration were found and excluded.

Data Management

Scopus allows for the export of the retrieved dataset to other programs such as Microsoft Excel or VOSviewer. For each article, the following information was exported to Microsoft Excel: title, abstract, author names, author affiliation, name of the publishing journal, number of citations received until the date of analysis, date of publication, funding source (if any), and author keywords.

Bibliometric Analysis and Mapping

The bibliometric analysis included a descriptive analysis of the number of publications per time, the most active journals in publishing articles, the most active countries, institutions, and authors involved in publishing articles, and the top cited papers. The bibliometric analysis also included visualization maps created by VOSviewer software program [25]. Important features in the visualization map included: (1) the color of the node, which denotes the cluster to which it is allocated; (2) the size of the node, which reflects its frequency of occurrences; (3) the distance between nodes, which determines how closely the nodes are related; and (4) the thickness of the connection between two nodes, which indicates the strength of their relationship. An author keyword co-occurrence map was used to identify the conceptual structure of the field, where clusters in the co-occurrence map represent the topical foci addressed in the literature on the detention and deportation of migrants.

Results

Volume and Characteristics of the Retrieved Articles

The search query found 906 articles published from 1982 to 2022. One-third (n = 309; 34.1%) of the articles were published in open-access sources. The majority of the articles were in English (n = 851; 93.9%), while the remaining 55 (6.1%) were bilingual, with English and non-English titles and abstracts.

Citation Analysis

The retrieved articles received 15,054 citations, an average of 16.6 (95% Confidence Interval: 14.3–18.9) citations per article. There were 156 (17.2%) articles with no citations and twenty-six (2.9%) with at least 100 citations each. The number of citations showed a positively skewed distribution. The median number of citations was 5 (interquartile range: 1–17).

Growth Pattern of Publications

Figure 1 shows the growth trajectory of publications on the detention and deportation of migrants. The earliest publication was recorded in the early 1980s. The growth pattern of publications included three phases: an emergence phase (1982–2001), in which the number of publications remained low; a fermentation phase (2002–2010), with a sudden increase in the number of publications; and a take-off phase (2011–2022), during which the number of research articles per year has risen approximately four times.

Fig. 1
figure 1

Linear graphic representation of the annual number of publications on detention and deportation of migrants (1900–2022)

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Productivity: Core Journals and Subject Areas

The retrieved articles were disseminated through 422 peer-reviewed journals. The majority of the retrieved articles (n = 744; 82.1%) were published within the subject area of social sciences, while 162 (17.9%) were published within the subject area of health sciences. Table 2 shows the core journals (top five journals) in publishing articles in the field. The Journal of Ethnic and Migration Studies (n = 28; 3.1%) was the leading journal in the field. However, articles published in the journal of Citizenship Studies received the highest number of citations per article (n = 41.2). The majority of journals in the core list were in the field of migration.

Table 2 Core journals in publishing research articles on detention and deportation of migrants
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Productivity: Core Countries and Institutions

Researchers from 58 different countries participated in publishing the retrieved articles. Researchers from the United States (US) contributed the most, with 334 (36.9%) articles. Of the 334 articles published by the US researchers, only 46 (5.1%) included international authors, indicative of limited international research collaboration. Table 3 shows the core countries (top five). The core list included four countries considered destination countries for international migrants (the US, the UK, Australia, and Canada) and one considered a source country (Mexico). Articles published by scholars from Canada received the highest number of citations per article (n = 28.1). Even though the US contributed the most, the majority of core institutions were based in Australia. The University of Oxford ranked first with 30 (3.3%) publications, followed by the University of New South Wales, the University of Sydney, and Monash University (Table 4). However, scholarly articles published by the University of New South Wales received the highest number of citations per article (n = 37.8).

Table 3 Core countries in publishing research articles on detention and deportation of migrants
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Table 4 Core institutions in publishing research articles on detention and deportation of migrants
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Productivity: Core Authors

In total, 1988 author names contributed to the retrieved articles, an average of 2.2 authors per article. The majority (n = 456; 50.3%) were single-authored, 212 (23.4%) were two-authored, while the remaining 238 (26.3%) were multi-authored (≥ three authors per article). Bosworth, M. (the UK, Oxford University) and Essex, R. (University of Greenwich, London, United Kingdom) ranked first with 12 (1.3%) articles each. Table 5 shows the core authors (top five). Articles by Steel, Z. (University of New South Wales, Australia), received the highest number of citations per article. The authors in the core list are in the fields of migration, asylum, and mental health, as indicated in their Scopus profiles.

Table 5 Core authors in publishing research articles on detention and deportation of migrants
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Most Impactful Articles

Table 5 shows the top 10 cited research articles [26,27,28,29,30,31,32,33,34,35]. The list included six single-authored articles. Two articles on the list were about the impact of detention and/or deportation on children. Three articles on the list were about asylum. The top 10 articles were published in 10 different journals.

Research Topics

The research topics addressed in the retrieved literature were identified by the visualization of the most frequent author keywords in the retrieved articles. Figure 2 is a visualization of the author keywords with a minimum of 10 or more occurrences. The map shows 54 items. The size of a node on the map indicates the frequency of occurrence of the keyword represented by the node. The most frequent keywords on the map, other than those related to migrants, detention and deportation, were “human rights” and “mental health”.

Fig. 2
figure 2

Network visualization map of author keywords with minimum frequency of five times. Node size is proportional to frequency of occurrence of the retrieved literature and represents a research topic being addressed in the field

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Figure 3 is an overlay visualization of the most frequent author keywords. This type of map is used to investigate and show the most frequent author keywords as a function of time, with the most recent keywords representing potential future research directions in the field. The yellow nodes on the overlay map represent the most recent author keywords. For example, the term “COVID-19” appeared most recently in the retrieved articles. Other terms of current and possibly future research interest include alternatives to detention, crimmigration, health, and family separation (Table 6).

Fig. 3
figure 3

Overlay visualization map of author keywords with a minimum frequency of five times. Nodes with yellow color represent topics that are recent and of future research interest

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Table 6 The most impactful articles on detention and deportation of migrants
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Major Research Themes

The visualization of terms in the abstracts of the retrieved articles is used to identify the major research themes addressed in the field. In the visualization map, nodes with similar colors are grouped into one cluster, representing a research theme. There were four clusters on the map (Fig. 4) representing the following four general research themes: (1) detention and deportation of Mexican migrants by the US immigration enforcement and the impact of this on Mexican children and families, including family separation; (2) healthcare services and mental health of detained and/or deported migrants; (3) human rights and international law in the context of asylum seekers; and (4) detention and deportation in the context of border control, social movements against detention and deportation, and migration policies in different countries.

Fig. 4
figure 4

Network visualization map of terms in the titles and abstracts of the retrieved literature. Nodes with similar colors represent a general research theme in the field

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International Research Collaboration

Research collaboration among countries with a minimum contribution of 10 articles was visualized. Eleven countries met the criteria and their research collaborative ties were presented graphically (Fig. 5). The map showed four clusters with different colors. The US, Canada, and Mexico existed in one cluster, while the UK and Australia existed in one cluster. The remaining two clusters consisted of several European countries, distributed into two clusters. The research collaboration between the UK and Australia was the strongest based on the thickness of the connecting line. The map also showed relatively strong research collaboration between the US and Mexico as well as between the US and the UK.

Fig. 5
figure 5

Network visualization map of international research collaboration among countries with a minimum contribution of five publications. Countries with similar colors have close research interest and collaboration. The thickness of the connecting lines represent the strength of research collaboration

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Discussion

The increasing numbers of international migrants and the introduction of new immigration policies led to the expansion of migration detention systems in several destination countries, such as the US, the UK, Australia, and Canada. In many situations, the conditions and the subsequent health and legal impact of detention and deportation on migrants remain debatable. In the current study, the scientific literature on detention and deportation in the context of migration was analyzed to identify current hotspots and potential future research topics in the field. In the current, both descriptive analysis and visualization maps were presented.

In the current study, the annual number of publications showed a distinctive increase in the last decade. This increase was secondary to several factors that stimulated active research in the past decade. First, the increased implementation of security procedures after several horrible attacks in the US and Europe stimulated research on illegal migrants and their potential security threats [36]. Second, the increased public criticism that described detention facilities as prisons with torture and discrimination [37]. Third, human rights advocacy groups, raise concern about the legal procedures of detention and deportation and called for alternatives to detention [38, 39]. Fourth, the negative impact of detention and deportation on children and families [40, 41]. Fifth, the lack of adequate healthcare services and safety problems for people in detention centers stimulated scholars in the fields of sociology, law, and human rights to investigate the topic [42]. Sixth, the mass migration of forcibly displaced people from certain conflict areas. The ongoing Syrian and Ukrainian conflicts caused millions of refugees to flee to European countries, which stimulated new research on immigration policies, border control, immigration detention centers, and deportation [43]. The findings in the current study emphasized the impact of detention and deportation procedures on Latino and Mexican migrants. However, there was little, if any, research discussing the impact of these procedures on migrants and refugees from the Eastern Mediterranean region, such as Syrian, Iraqi, Yemeni, Palestinian, and Afghani migrants and refugees. In the case of Latino migrants, it is possible that the active and free media in the US and Latin America participated in increasing scholarly production in the field. Furthermore, scholars in source countries, such as Mexico, have been actively involved in researching the experiences of migrants in the detention and deportation process given the shared borders between Mexico and the US. However, the contribution of scholars in the African and Eastern Mediterranean regions was inviable.

The core countries, institutions, and authors showed the key role of scholars in the US, Canada, the UK, and Australia. These countries are destination countries for international migrants, and all are English-speaking countries, which facilitates the process of publishing in Scopus-indexed journals. The four countries have detention policies and systems that have been developed over the past several decades. Detention policies in these four countries include mandatory detention and/or indefinite mandatory practices using security or military infrastructure. Finally, these four countries represent liberal democracies that are transparent and open to comments and critique by human rights advocacy groups. Detention practices in the US started in the early 1980s in response to the migration of Cubans, Haitians, and Central Americans fleeing totalitarian governments and civil war [44]. Detention practices in the US have come under criticism from human rights advocacy groups [45]. In contrast to the US immigration detention policies, the Canadian policies are less negative and therefore have received less international criticism [46].

The visualization of the most frequent author keywords indicated that the mental health of detained or deported individuals and their families is an important research topic in the field. Two systematic reviews published in 2008 and 2018 reported higher levels of anxiety, depression, post-traumatic stress disorder, and other mental health problems among individuals during and post-detention [47, 48]. A study on seventeen adult refugees who had been held in an Australian immigration detention facility for a long time claimed that the psychological difficulties after release from migration centers were secondary to the negative experiences during the detention period [49]. Mistreatment of immigrants in detention centers has been identified as a risk factor for mental health problems during and post-detention [50]. Several studies indicated that the detention and deportation of a family member are associated with economic hardship, health, and well-being issues among adolescents and other family members [51]. Another research topic deduced from the visualization map was human rights violations and international law. Detention is the deprivation of freedom of movement, which is an interference with basic human rights. Therefore, detention must be used as a last resort when necessary and for a limited period. Despite this, detention is a common practice in many countries [39, 52]. The human rights violations of immigration detention centers are intensified due to the inhumane treatment and criminalization of migrants [53]. In addition, the privatization of detention centers further intensified the human rights violations in these centers [23, 54].

The COVID-19 term appeared in the recent literature on the detention and deportation of migrants. During the first few months of the COVID-19 pandemic, concerns were raised about the safety and health of detainees [55, 56]. Reports on the spread of COVID-19 in detention centers led to serious consequences [57]. The COVID-19 pandemic has changed detention practices and conditions such as distancing, using protective tools, and limiting visitation procedures [58]. The COVID-19 pandemic raised the question of the value of immigration detentions, especially for indefinite periods. Prolonged or indefinite detention is considered a violation of international human rights law. Therefore, detained people in certain detention centers implemented hunger strikes or other types of practices to object to and end the inhumane practices in the confinement centers [59]. Alternatives to detention for non-citizens have been suggested to achieve the objective of detention without harmful or inhumane practices. Alternatives to Detention (ATD) plan is more respectful of human rights because the ATD policies ensure that asylum seekers/refugees/irregular migrants are not detained for reasons related to their citizenship status [60].

Research Gaps

The analysis in the current study revealed several research gaps. First, research on access to and healthcare services offered in detention centers needs to be conducted to ensure justice and the right to proper healthcare services for detained migrants. Second, research on the detention and deportation experiences of migrants from the Eastern Mediterranean, African, and Asian regions needs to be investigated and published. Third, participation and research collaboration with scholars from source countries need to be increased to strengthen the debate and discussion about migration policies in both destination and source countries. Fourth, detention and deportation are of interest to scholars from different scientific disciplines. Therefore, scholars from the fields of social and health sciences need to collaborate in this field. Fifth, editors of public health journals need to focus on health issues related to detention and deportation of migrants since the contribution of public health journals to the field was limited.

Potential Future Research

The current study is not without limitations. The search query was developed based on the title search. The use of the title and abstract search is more comprehensive, but yields more false positive results. It is expected that the results obtained in the current study might represent an underestimation of the true volume of the scientific literature on migration detention and deportation. Furthermore, the search was limited to scientific literature, while there is plenty of grey literature published by governments and international organizations, including human rights organizations. Despite these limitations, the current study was the first to give an insight into the scientific literature on detention and deportation to support the implementation of alternative strategies to migration detention. The current study is not meant to criticize a specific country; rather, it is meant to promote research and support advocacy groups to pressure governments to implement international laws regarding immigration detention and deportation.

Conclusions

Analysis and mapping of the scientific literature on the detention and deportation of migrants showed that research in the field has grown substantially in the past decade. The findings of the current study highlighted the key contributors to the research field. Although irregular migration occurs throughout the world, research on detention and deportation was limited to a few key countries and institutions, with a special focus on the US detention and deportation of Latino migrants. The healthcare services, human rights, and legality of detention and deportation in many countries are either uninvestigated or no permission is given to researchers to investigate such issues due to security reasons. Future research should concentrate on ATD with the full observation of international human rights laws. Furthermore, future research on the detention and deportation of non-Latino migrants is required.