Rise of migration as a research field

Between fragmentation and
institutionalisation: the rise of migration
studies as a research field

Nathan Levy* , Asya Pisarevskaya and Peter Scholten
* Correspondence: levy@essb.eur.nl
Department of Public
Administration and Sociology,
Erasmus University Rotterdam,
Rotterdam, Netherlands
Abstract
It is clear that the field of migration studies has grown significantly over the past
decades. What is less known is how this growth has taken place. This article
combines bibliometric metadata with expert interviews to analyse the
institutionalisation of the field in terms of self-referentiality, internationalisation, and
epistemic communities. Self-referentiality in migration studies has gradually increased
as the field has grown, until recently. The field has internationalised in terms of
international co -authorships but has done so unevenly. Finally, we find that
epistemic communities in migration studies, based largely on disciplines, increasingly
refer to one another and are increasingly interdisciplinary.
Introduction
We know that the field of migration studies has grown significantly over the past decades (Pisarevskaya et al. 2019). This is manifest in the increase of the number of publications, journals, research institutes and undergraduate programs. This development
in size says something on the relevance as well as the popularity of migration studies.
What is less known is how this growth of migration studies has taken place. Does this
growth involve an institutionalisation of migration research field as a research field?
Or has growth come with a growing fragmentation of studies on migration? Our aim
in this article is to provide empirical reflections on this process. There are studies that
look at specific aspects of this process, for instance in terms of interdisciplinarity
(Bommes and Morawska 2005), theoretical (Massey et al. 1998; Cohen, 1996) and
methodological (King 2012; Vargas-Silva 2012) developments, but research with a holistic approach is lacking. Our research question, therefore, is how has migration studies
institutionalised in the past four decades?
We examine institutionalisation from a three-fold perspective, drawing on migration
studies and sociology of science literature. Firstly, we analyse self-referentiality – the
extent to which researchers on migration refer to one another. Then we study internationalisation – the extent to which migration researchers have collaborated across
countries and continents. The third aspect we analyse are epistemic communities –
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Levy et al. Comparative Migration Studies (2020) 8:24
https://doi.org/10.1186/s40878-020-00180-7
groups of scholars congregated around certain themes, methods, disciplines, or concepts. Together, these three dimensions provide a comprehensive understanding of developments in the migration studies field in terms of both structures and cultures of
knowledge production (cf. Kuhn 2012; Hess, 1997).
We investigate the institutionalisation of migration studies by mapping 48,842 migrationrelated Web of Science records (1975–2018) in the VOSViewer software (van Eck and
Waltman 2009), namely by looking at when, where, and between whom collaboration and
citation networks have occurred. Furthermore we interpret these collaborations and citation
networks through qualitative insights gathered from interviews with long-standing experts
in the field and from secondary literature. Thus, we pursue an iterative approach which triangulates between quantitative data, qualitative interviews, and literature.
There are at least three reasons why study of the institutionalisation of the field is important. First, for scholars who are potentially immersed in their own sub-fields or disciplines,
this study provides an historical overview of the development of the broader migration research field. This expands one’s horizons on what is out there in migration studies beyond
one’s epistemic milieu. As migration scholars, we cannot understand where we are without
seeing how we got there. This is not without limitations of course. Web of Science’s coverage of the social sciences and especially the humanities is limited compared to the natural
sciences (see Aksnes and Sivertsen 2019), therefore the bibliometrics offer an approximation
which is complemented by experts’ input. Second, interdisciplinarity (Borkert 2018; Brettell
and Hollifield 2015) and internationalisation (Thränhardt and Bommes 2010) are increasingly promoted as the means of scientific innovation. Therefore, a state of the art and historical re-tracing of these processes is needed. Third, since research is widely perceived as
fragmented given the rapid growth of migration studies, it is necessary to see whether the
claim of fragmentation is supported by bibliometric evidence.
The development of research fields
Research fields are institutionalised areas of study that build on as well as contribute to one
or several disciplines. They have a specific thematic focus and a specific research infrastructure (such as their own conferences, institutes and educational programmes). A key question is whether migration studies has institutionalised as a research field, and if so, how its
focus (culture of knowledge production) as well as infrastructure (structure of knowledge
production) have taken shape. By “structure”, we refer to how research is organised geographically, organisationally (including financially), and in terms of publication venues (e.g.
journals). “Culture” in knowledge production here refers to how researchers “organically” or
even unintentionally cluster around themes, disciplines, and even structures as they are referred to above, forming, in other words, epistemic communities (Knorr, 1999).
Before analysing its development, it is important to define what constitutes ‘migration
studies’. Here we take a definition that follows King (2012): migration studies encompasses research on all types of international and internal migration, migrants, and
migration-related diversities. When mentioning research on migration, this paper is referring to all of these aspects. Although its origins lie with Ravenstein (1885) and early
twentieth-century sociology, such as Thomas and Znaniecki (1918), this field has
emerged with its own journals and institutes since the 1960s, with intensified growth
since the 1990s (Pisarevskaya et al. 2019).
Levy et al. Comparative Migration Studies (2020) 8:24 Page 2 of 24

Institutionalisation can be explored through the phenomenon of self-referentiality
(Shinn 2002, pp. 600–601). If migration researchers regularly refer to one another, then
they are likely to share a common theoretical language and explicit or implicit expectations underpinning their research practices, which is an indicator of institutionalisation
(cf. Scott 2008). The following two aspects delve more deeply into the where and how
questions of institutionalisation. Given the peculiarity of the subject of migration as a
global phenomenon, it is especially important to consider the internationalisation of
knowledge production (Winter 2014). Studying migration from only a national perspective, as several critiques during the 2000s observed (Wimmer and Glick Schiller 2003;
Thränhardt and Bommes 2010; Favell 2003; 2015), inhibits our epistemological understanding of migration. Then, analysing epistemic communities provides us with an understanding of the field’s institutionalisation by revealing a potential array of organically
emerging sub-fields, or paradigms (Kuhn 2012), focused around specific disciplines or
themes. Taken together, these three aspects give us further insight into the theoretical
maturity of the field that we previously theorised (Pisarevskaya et al. 2019).
In this study, we take an iterative approach to theory-building. In order to develop
expectations for the empirical bibliometric analysis, we combine theory from published
literature with information gathered from the expert interviews with long-standing
scholars in migration studies (see Methods section). Below, we present the debates regarding the three aspects of institutionalisation mentioned above.
Self-referentiality
Knowledge production on migration has occurred for over a century (see Greenwood
and Hunt 2003), encompassing a number of research traditions and methodologies
(Brettell and Hollifield 2015; Bommes and Morawska 2005; Vargas-Silva, 2012). The
field has grown significantly in recent decades (Pisarevskaya et al. 2019), to the extent
that one might consider the present not only to be an “age of migration” (Castles et al.
2014), but an “age of migration studies” (Hatton 2011).
There is no clear consensus on how the growth of the field relates to the level of selfreferentiality in migration studies. On one hand, some commentators note fragmentation in the field. They observe a lack of “synthesis” between different approaches, disciplines, and levels of analysis (Penninx et al. 2008, p. 8; Kritz et al., 1981; Massey et al.
1998; King 2012; Scholten et al. 2015, pp. 331–335). On the other hand, recent studies
find that this thesis may be overstated. Topical analysis of the field suggests that it has
a rather unified and stable conceptual and theoretical foundation, observed in increasing connectedness of topics in the past decade (Pisarevskaya et al. 2019).
Moreover, efforts to give structure to the field in recent decades may have led to a
standardisation of norms and practices. For example, several migration-focused journals have been established during and since the 1990s (Pisarevskaya et al. 2019). Some
of our expert interviewees noted the concerted efforts throughout the 1990s to formalise research on migration (see also Thränhardt and Bommes 2010). This included the
establishment of a migration programme (1994) in the US by the Social Science Research Council (SSRC); the Network of Migration Research on Africa (NoMRA) in
1998; and a series of migration research institutes in Europe, including the Centre for
Race and Ethnic Relations (CRER, Warwick), Institute for Migration & Ethnic Studies
Levy et al. Comparative Migration Studies (2020) 8:24 Page 3 of 24

(IMES, Amsterdam), Institute for Migration Research and Intercultural Studies (IMIS,
Osnabrück), the Sussex Centre for Migration Research, and many more since, leading
to the founding of the IMISCOE network (2004).
We therefore expect (E1) that our analysis of citation patterns will reconfirm the
findings of the topic analysis of Pisarevskaya et al (2019). Despite intensified growth in
the volume of knowledge in migration studies, the field has evolved from a disparate
set of publications in the 1970s, into an increasingly self-referential field of study from
the 1990s on.
Internationalisation
Since the 2000s, much has been written on the ontological and political consequences of
“national model” (Bertossi and Duyvendak 2012) or “national paradigm” (Thränhardt and
Bommes 2010) structures of knowledge production in migration studies. This is also
linked to critiques of “methodological nationalism” (Wimmer and Glick Schiller 2003;
Favell 2003; 2015). Migration research has traditionally been connected to national histories, policies, and narratives of migration, as well as languages, enshrined by established
funding procedures and sources of empirical data, i.e. national censuses. Given these discussions and the increasing digitisation of knowledge infrastructures enabling easier international communication, one might expect a concurrent increase in cross-country
collaborations (cf. Winter 2014). While cross-country collaborations may not necessarily
mean the end of national paradigms, continued scientific co-operation across borders facilitates a broadening of conceptual and theoretical perspectives, a softening of national
models, and, perhaps, a globalisation of migration theory.
Research policy and funding structures also play a role in internationalisation which
can lead to an unevenness of this process across the globe (see Carling, 2015). For example, in the European Union, knowledge production has become “Europeanised”
(Geddes and Scholten 2015). Research on migration has been co-ordinated crossnationally in large part through IMISCOE, an EU Network of Excellence established in
2004, which has operated independently since 2009. We expect this initiative to have
contributed to weakening national paradigms in this region. However, the interviewees
remarked that due to a tendency to publish in their own language, French, and to a
lesser extent, German migration research might not be as transnational as other European countries, including in the post-2004 “IMISCOE” era.
Where English is generally the lingua franca of western migration research, the linguistic diversity in Asian scholarship, according to one interviewee, means that a network such as IMISCOE has not taken off to the same extent. Another interviewee
points out that although NoMRA exists for all of Africa, its activity has been concentrated in five key countries: Nigeria, Ghana, Kenya, Mozambique, and South Africa. According to this interviewee, such countries, due to limited domestic research funding,
may avoid national paradigms, given the international nature of both their funding and
research collaborations (see also van den Boom 2010). In the USA, as the country
which produces more migration research than any other, there have been attempts to
internationalise, but, as some interviewees commented, these have largely failed, due to
a tendency to replicate American conceptualisations in foreign contexts. Meanwhile, as
one interviewee noted, the establishment of the Metropolis network in Canada in the
Levy et al. Comparative Migration Studies (2020) 8:24 Page 4 of 24

1990s has led to a number of fruitful international collaborations between there and
other – mainly European – nations.
In general, we expect that migration studies has become an internationalised field
since the turn of the century, but not an entirely globalised one (E2). We expect migration studies to have become more internationalised in most European countries,
Canada, and in some African countries, but to have internationalised to a lesser extent
in the USA, France, Germany, and most Asian countries (E3).
Epistemic communities
Analysis of epistemic communities gives us an insight into the cultures of knowledge
production in migration studies over the years. By ‘epistemic communities’, we refer to
networks of scholars that have emerged (and disappeared) around certain topics, concepts, approaches, or disciplines.
There has been a long-standing question of whether or not migration studies is
truly interdisciplinary, or transdisciplinary.1 Given that migration studies is a research area that is approached from different disciplines, it is interesting to consider whether the “virtually unbreakable” structure of those disciplines (Abbott
2001, p. 149) has remained, or become less rigid over time, indicating crossdisciplinary osmosis. Over the past two decades, Brettell and Hollifield (2000, 2008,
2015) have invoked this discussion in their three editions of Migration Theory, arguing that by now we see more interchange among disciplines. However, Favell
(2003; 2015, p. 319), in his epilogue to the latest edition, argues that Europe is
more “post-disciplinary” than elsewhere. This may be related to the incentivisation
of interdisciplinarity in major funding organisations, such as the European Union’s
Horizon 2020 programme (see European Union 2016).
On this basis, we expect to find that up until the 1990s, researchers of migration were
divided according to disciplinary structures. From the 1990s onwards, we expect to find
cross-disciplinary osmosis and the breaking down of these divisions (E4).
The published research suggesting concrete developments in the fieldin this regard is
rather limited. We do know, however, that there is a plurality of paradigms employed in
migration research, revolving, for instance, around opposing sides of the ‘dyads’ in migration studies that Cohen (1996) identifies, such as internal versus international migration.
They may also be tied to more specific themes such as second-generation migrants, gender and migration, or the governance of migration-related diversity (cf. Portes 1997; King
2012). Analysis of such evolutions can be conducted through a multitude of lenses. Therefore we take an iterative approach using the qualitative input of our expert interviewees to
trace some interesting patterns. By no means, we claim this description to be exhaustive,
however, it still provides valuable insights into some key developments in the field. These
include the examination of paradigmatic divides in the field such as Cohen’s ‘dyads’
1
E.g. a transdisciplinary article is one where it becomes difficult to ascertain the discipline from which it has
originated, even though it is clearly identified as belonging to migration studies conducted an Englishlanguage complex query (see Additional file 1) to gather our data. This generated 48,842 items, which are displayed per year in Fig. 1. These include journal articles, editorials, commentaries, and reviews, but unfortunately not books. However, as this article is concerned with general trends in the field not with analysis of
the most influential publications, as Sirkeci et al. (2017, pp. 399–403) have already done, this is not a major
limitation. The publications are produced by 44,286 different authors, publishing in 1512 different sources,
based at 9052 different organisations, in 185 countries. See details about trends over time for each of these
aspects in the Additional file 1.
Levy et al. Comparative Migration Studies (2020) 8:24 Page 5 of 24

(1996); the questions of primacy of certain topics i.e. a claim that migration studies’ have
emerged from the ‘shadows’ of ethnic and racial studies in the 1970s–1990s; the proliferation of transnationalism from the mid-1990s onwards; and the “cultural turn” of migration
research from being predominantly quantitative and demographic-focused, towards more
nuanced qualitative studies of migration (E5).
Methods
This article employs an iterative approach combining bibliometric analysis of Web of
Science data, using the VOSviewer software, and qualitative data gathered from 10 interviews with long-standing experts in migration studies. The metadata were collected
from the Web of Science index on 12 March 2019. We used Erasmus University
Rotterdam’s subscription, which has access to records going back to 1975. We conducted an English-language complex query (see Annex) to gather our data. This generated 48,842 items, which are displayed per year in Figure 1. These include journal
articles, editorials, comentaries, and reviews, but unfortunately not books. However, as
this articel is concerned with general trends in the field not with analysis of the most
infuential publications, as Sirkeci et al (2017, pp. 399-403) have already done, this is
not a major limitation. The publications are produced by 44,286 different authors, publishing in 1512 different sources, based at 9052 different organisations, in 185 countries.
See details about trends over time for each of these aspects in the Annex.
Bibliometric data provide empirical evidence of the structure and culture of the field,
and interviews help us to interpret the data (cf. Gläser et al. 2017). Because they were
conducted before the bibliometric analysis, the interviews served a double purpose of
(i) developing, as seen above, our theoretical expectations, and (ii) of elaborating our
qualitative interpretations of the data (cf. Charmaz 2001).
Expert interviews
To enrich our knowledge of the development of migration studies, expert interviews
were conducted between March and May 2019. In total, 10 experts were selected. The
criterion for the selection of the experts was that they had published commentaries or
been instrumental in the development or institutionalisation of migration studies,
whether globally or locally. Our interviewees have worked in Sub-Saharan Africa, East
Asia, Europe, the Middle East, North America, and Oceania.
• Prof. Aderanti Adepoju
Founder, Network of Migration Research on Africa (Lagos)
• Prof. Stephen Castles
Former Director, International Migration Institute (Oxford)
• Dr. Yuk Wah Chan
Organiser, Network for Asian Migration Studies (Hong Kong)
• Dr. Josh DeWind
Director of Migration Program, Social Science Research Council (New York)
• Prof. James Hollifield
Director, Tower Center, Southern Methodist University (Dallas)
• Prof. Russell King
Former Director, Sussex Centre for Migration Research (Brighton)
Levy et al. Comparative Migration Studies (2020) 8:24 Page 6 of 24

Methods (Continued)
• Prof. Peggy Levitt
Co-founder, Global (De) Centre (Cambridge, MA / Florence)
• Prof. Douglas Massey
Co-director, Mexican Migration Project (Princeton)
• Prof. Rinus Penninx
Founder, IMISCOE Network of Excellence (Amsterdam)
• Prof. Steven Vertovec
Director, Max-Planck-Institute for the Study of Religious and Ethnic Diversity (Göttingen)
The interviews followed a semi-structured format in which the interviewees were
asked in advance to prepare their ideas on the following themes in migration studies:
institutionalisation; internationalisation; interdisciplinarity; key concepts, publications,
authors, and institutes; and defining periods in the history of the field. The interviews
ranged from 45 min to 2 h in length. We coded and summarised the key points related
to each theme, by interviewee, in a spreadsheet.
Bibliometric analysis
We conducted various analyses using VOSviewer (v.1.6.7 and v.1.6.11; van Eck and
Waltman 2009) to probe our theoretical expectations. We explored the bibliometric
and citation trends over time, to determine whether migration studies has become
more or less self-referential, international, and/or, by the standard of our analytical
framework, institutionalised, including multiple epistemic communities.
For measuring how self-referential the dataset was, we conducted citation analyses at
both document and source level. A citation analysis looks at the citations between
documents and sources within the dataset, regardless of citing direction. If a large body
of literature such as this one, sharing a thematic focus, is not at the document level, we
analysed the proclivity of documents with 30 or more citations in the dataset (N =
3466) to cite one another. By only analysing highly-cited papers (HCPs, see Plomp
1990), we focus on the ‘influential core’ of the field. While this method also has a bias
in terms of emphasising older documents that have had more time to gather citations
(Nakamura et al. 2011), increased overall self-referentiality, controlled for by the overall
number of HCPs, could indicate the institutionalisation of the field. A source-level analysis usually considers citations between journals (N = 1431). This tells us whether,
with a growing number of journals (see Additional file 1), the field became
fragmented.
For sources, we conducted an additional analysis of network density. This gives an
indication of how self-referential the field has been compared to how self-referential it
could theoretically have been. By adding each consecutive year to the starting year, we
calculated the density of the citation network using a slightly adjusted version of the
formula employed by Reagans and McEvily (2003):
Where D is density, and t indicates the period from 1975 until each of the
consequent year. The cumulative potential number of links is calculated using this
formula:
Levy et al. Comparative Migration Studies (2020) 8:24 Page 7 of 24
¼ 2ð−1Þ

, where N is a Total number of sources for period t.
The internationalisation of the field was measured by the likelihood of migration
scholars to collaborate across borders. This provides a more meaningful view of
internationalisation than merely studying the increase in diversity of countries
producing migration research. For this reason, we follow Yarime et al. (2010), and
operationalise collaboration as co-authorship. An increased proclivity to co-author
internationally could potentially indicate that the weakening of national paradigms in
migration research.
This analysis was limited to the years 1998–2018, because VOSviewer was only able
to identify sufficient geographic metadata from 1998 onwards (Fig. 1). To measure the
proportion of transnationally-structured research, we divided the total annual number
of international co-authorships by the total annual number of articles containing geographic metadata. We did this analysis per country2 as well as globally.
Finally, to explore the development of epistemic communities, we used co-citation
analyses at the author level. This type of analysis allows us look behind the tapestry of
citations in migration studies, and understand which authors constitute the reference
bases for the literature. Co-citation network maps display the links between authors
from within or beyond the dataset that are cited together in the documents within the
dataset. In other words, these maps unveil latent communities of scholars who have
been linked together by others. For feasibility reasons, we set the threshold to authors
who have received 10 or more citations. This way we exclude authors who have influenced the field to a lesser extent.
– i.e. “early 1980s”, “late 1990s” – as our interviewees described their perception of
the field’s development. VOSviewer clusters the authors according to how often they
are cited together. We take these clusters to approximate the variety of epistemic
communities within the field in each period. To assign labels, we used Google Scholar
to find the unifying features of each cluster. We checked the research of each cluster’s
most-cited authors, and the first-page results (usually the authors’ higher-cited works)
Fig. 1 Number of items, per year, in migration studies dataset based on advanced query of Web of Science,
12 March 2019
2
See sheet ‘all countries weighted’ for relativized co-authorship statistics. We did this in 5 year increments
(1975–1979; 1980–1984, and so on, with the exception of the final period, 2015–2018). The network files
exported from VOSviewer can be found in the Harvard Dataverse (see Levy, et al., 2019). Following our iterative logic, this enabled us to analyse the data in the same terms
Levy et al. Comparative Migration Studies (2020) 8:24 Page 8 of 24
enabled us to grasp their conceptual, thematic, or disciplinary focus. We triangulated
this information with the reflections shared by our expert interviewees.
We supplemented the qualitative analysis of co-citation networks with a few basic
quantitative network measures. Concretely, in each period of time we measured the size
of the reference basis (in terms of total number of authors co-cited), the density of co
-citation networks, and the average path length, to examine the epistemic communities’
connectedness to one another across time.
Here it is worth repeating that bibliometrics offer an empirical approximation of the
development of the field. Due to the limitations of using Web of Science data, our
analysis may underestimate the contributions that historians and anthropologists have
made to the field, as well as researchers publishing in languages other than English.
This is, in part, why the bibliometric analysis is combined with expert input.
Results and analysis
Self-referentiality
Despite intensified growth in the volume of knowledge in migration studies, we
expected to see the field become increasingly self-referential over the past four decades,
particularly during and after the 1990s. In line with our previous work (Pisarevskaya
et al. 2019), we indeed see intensified growth in the number of publications (Fig. 1), authors, organisations, sources, and countries (Additional file 1) publishing on migration,
especially since the mid-2000s. In line with our expectation, Fig. 2 shows that, over
time, the overall likelihood of research in our dataset to cite other research in our dataset has increased. This is the case for both highly-cited documents (HCPs), and for
sources.
Figure 3 shows the analysis of actual citation links versus potential citation links at
the source level. From the mid-1970s (0.02%, or 6 out of 11,000 potential links) until
the late 2000s (0.65%, or 888 out of 138,000 potential links), a gradually higher and
higher proportion of the potential citation connections within migration research
sources were exploited. Since the late 2000s, the network density has stagnated and
gradually declined. The reason for this negative trend in recent years is possibly related
to “citation lag”, whereby influential research, particularly in interdisciplinary fields,
does not tend to begin accumulating citations for around 5 years (Nakamura et al.
Fig. 2 Inter-HCP and inter-source citation rates
Levy et al. Comparative Migration Studies (2020) 8:24 Page 9 of 24

2011, pp. 228–230). While the stagnation in the years 2008–2013 could be due to an
exponential growth in the number of sources (see Fig. 4).
Taken together, these findings give support to our expectation (E1). By looking at
influential papers and sources publishing on migration, we see that the field has
generally become more self- referential, which indicates a trend towards
institutionalisation. However, when the self-referentiality of the sources is compared
against a theoretical threshold of all possible connections, we see that the percentage of
actual citation links increases up to a point. Since the late 2000s, the proliferation of
sources has intensified to much higher extent than have the actual inter-source connections. This does not necessarily undermine the process of institutionalisation; it may
simply be due to citation lag, or indeed it could be related to the mainstreaming of migration research ‘back’ into traditional disciplines. The epistemic communities section
will elaborate on this.
Internationalisation
We expected migration studies to have internationalised, but to have done so unevenly.
As Fig. 5 shows, we see that the overall proclivity of migration researchers to
collaborate internationally has significantly increased over time, particularly since the
mid-2000s. In 1998 there were 38 international co-authorship links, representing 47
countries, across 726 articles. In 2018, there were 636 international co-authorship links,
representing 104 countries, across 2767 articles. In other words, around 5% of
Fig. 3 Density of citation links between sources (journals) in migration studies, 1975–2018
Fig. 4 Number of publication sources, per year 1975–2018
Levy et al. Comparative Migration Studies (2020) 8:24 Page 10 of 24
Fig. 5 Number of international co-authorships, controlled for number of documents, 1998–2018
Fig. 6 Visualisations of cross-national co-authorship links in 1998 – top and 2018 – bottom
Levy et al. Comparative Migration Studies (2020) 8:24 Page 11 of 24

migration research published in 1998 was cross-nationally co-authored, and around
23% in 2018. Figure 6 visualises this development in terms of the most strongly connected countries. The size of a node reflects the respective country’s number of crossnational co-authorships. The thickness of a link reflects the number of co-authorships
between the countries at either end.
A deeper probing of the data unveils an uneven internationalisation taking place
(Table 1). We see that among the two regions with the largest overall output the trend
of internationalisation is substantially stronger in Europe than in North America. In
Europe, despite linguistic diversity, critiques of national paradigms have perhaps landed
on fertile soil. Research policy at the European level has particularly played a role in
this. For example, in the 2000s the European Union’s FP6 introduced Networks of
Excellence (NoE; see de Baas and Vallés 2007) and established the IMISCOE NoE. Our
interviewees regarded this as a key turning point for internationalisation. Furthermore,
FPs since then have encouraged international collaboration.
In Asia and Oceania, a significant amount of research is also internationally coauthored, but the volume of output is much lower. As for Middle Eastern, African, and
South American countries, there is an even lower volume of research, but with a much
higher proportion of international co-authorships in Sub-Saharan Africa and South
America. Relatively little Middle Eastern migration scholarship is internationally coauthored. These disparities are very likely down to the English-language focus of our
dataset, or also the extent of Web of Science’s coverage of journals in developing countries. Nevertheless, what this analysis shows is that perhaps there is a relationship
between international collaborations in Asia, Africa, and South America, and the probability of being published in English-speaking international journals.
Delving into the country details (Table 2), to our surprise, we can see that German
and French migration scholarship is overall among the most internationally
collaborative (51%). However, since a large body of French- and German-language literature is probably not included in our dataset, this indicator may be limited.
As expected, among North American countries, the proclivity to collaborate was
comparatively lower. For example, the United States, the high absolute number of
international co-authorships comprise a relatively low percentage (13%) of its overall
extensive output. To illustrate this trend, our interviewees gave the example of the Social Science Research Council’s International Migration programme, which, despite
Table 1 International co-authorships by region, 1998–2018 (only countries with over 30 articles)
Region International co-authorships
as share of articles
International
co-authorships (total)
Articles (total)
North America 15% 2150 14,724
Europe 36% 4852 13,559
Asia 44% 851 1944
Oceania 32% 576 1804
MENA 28% 212 750
Africa 67% 282 423
South America 61% 214 353
Grand Total 27% 9137 33,557
Levy et al. Comparative Migration Studies (2020) 8:24 Page 12 of 24

Table 2 Countries with >40 international co-authorships 1998-2018
COUNTRIES WITH > 40 INTERNATIONAL CO-AUTHORSHIPS, 1998–2018
Countries Abs. N of intl. collaborations As percentage of total output
Slovakia 40 91%
Nigeria 43 90%
Chile 69 85%
Austria 154 72%
Poland 80 68%
Belgium 258 62%
South africa 202 60%
Portugal 65 57%
South korea 98 53%
Taiwan 54 52%
Germany 515 51%
France 249 51%
India 70 51%
Switzerland 151 50%
New zealand 144 49%
Mexico 98 49%
Greece 51 49%
Brazil 85 46%
Italy 249 45%
Scotland 180 44%
Singapore 79 42%
Netherlands 538 41%
China 362 41%
Spain 275 41%
Turkey 102 40%
Japan 88 40%
Wales 51 40%
Finland 91 39%
Malaysia 50 39%
Russia 74 38%
Norway 129 37%
Sweden 197 35%
North ireland 47 35%
Ireland 69 34%
Denmark 105 33%
Australia 432 29%
Canada 477 24%
England 1196 22%
Israel 110 22%
Usa 1575 13%
Levy et al. Comparative Migration Studies (2020) 8:24 Page 13 of 24

aiming at internationalisation, was rather US-centric, replicating US-developed concepts and theories (Portes and DeWind, 2004, pp. 845–847). Canada is somewhat more
internationally collaborative, which is possibly due to its historical involvement in the
Metropolis International Network, which was emphasised by several interviewees.
South Africa and Nigeria have been leading African countries in terms of
publications and international co-authorships. Especially in the past decade, these have
been joined by Kenya, Mozambique and Ghana (see Levy, et al., 2020), where migration
research institutes have recently been established. This is in line with the perception of
our interviewees.
In Asian scholarship, as Table 2 shows, there are a large number of cross-national
collaborations involving China. This is likely related to international interest in the
country’s ‘floating population’, as the world’s biggest case of internal migration (see
Xiang and Tan 2005). Singapore, Japan and Taiwan are also among the most internationally collaborative Asian countries. Our interviewees regarded these as migration
research hubs, for instance due to the migration focus of the Asia Research Institute at
the National University of Singapore.
To sum up, the absolute and relative increase in international co-authorships in migration studies might be a consequence of the critiques of national paradigms which
emerged in the early 2000s, although the structural context may have facilitated this
trend (cf. Henke 2001, p. 595). In this period, the digitisation of science has provided
the general context in which internationalisation has taken place, but differences persist
in terms of the uneven internationalisation that we have theorised. Our evidence indicates that varied levels of internationally-oriented research policies, on the one hand,
and global inequalities of knowledge production, on the other, may have also played a
role in different levels of internationalisation across regions.
Epistemic communities
Whereas self-referentiality and internationalisation are indicators of structural institutionalisation, another side of institutionalisation involves more the substance of knowledge production, or the ‘culture of knowledge production. Therefore, in this section,
we bring together the themes discussed above and elaborate on the argument that
within migration studies there are several sub-areas that have evolved over time. These
developments can be traced using co-citation analysis, which shows authors who are
often referred to, regardless of the type of publication (including books), in migration
literature. It is important to emphasise that these are not necessarily authors who cite
each other. Authors who are often cited together (co-cited) in one document form a cluster. These clusters can be interpreted as epistemic communities, or so to say, discursive
spaces, reflecting the way in which authors position themselves in wider conceptual discussions. A common reference basis allows scientists to engage in meaningful discussions
on theory and methodology. Therefore, the frequent co-citation of authors indicates a
shared epistemic foundation from which the citing literature stems. Of course, authors
whose work is criticised may be co-cited with others whose theory or method one adopts.
Nevertheless, such co -citation still points to the existence of a shared epistemic community within which such debates make sense, since the citing researchers know about the
existence of the authors they disagree with and deem relevant to distinguish their own
Levy et al. Comparative Migration Studies (2020) 8:24 Page 14 of 24

approach from those who are being criticised. These reference communities may be thematically -, disciplinarily- and even geographically-bound, in light of the uneven internationalisation discussed in the latter section.
Here we demonstrate the findings from this analysis and how they relate to the
insights obtained from the expert interviews.
Reference islands: (cross-)disciplinary themes
From the late 1970s to late 1980s migration research was divided into several distinct
clusters, pointing at the existence of separate reference ‘islands’ (bubbles), cited by
different groups of scholars (Fig. 7). The main three groups we define are
“Assimilationists” (red), “Economic sociologists” (dark blue) and “Economists” (light
blue), “Demographers” (green), “Refugee studies” (violet). The assimilationists’ and
demographers’ clusters seem to have the least in common, as they are positioned on
the opposite sides of the network. The epistemic community of “Assimilationists” were
during this time discussing the process of migrant adaptation and inter-group relationships, while “Demographers” worked largely on issues of fertility and mortality across
various ethnic groups and migration statuses. Overall, there is a clear divide between
cultural sociologists, economic sociologists, economists and demographers. These dispersed groups are connected via the US census as a data source, indicating that migration studies then were largely US-based.
In the next 10 years (Fig. 8) we see that the cluster of “Assimilationists” (red)
changed, and some authors of the previous decade were grouped into other clusters.
New names, such as Smith, Liberson, Banton, Asante and Davidson were cited the
most, and therefore a new name “Race and ethnic relations” seems to be more
appropriate for this cluster (red). From this period on, critical black scholars became
increasingly prominent in this sub-field, such as Gilroy, Hall, Du Bois, Eduardo BonillaFig. 7 co-citations 1975–1984 (N = 554)
Levy et al. Comparative Migration Studies (2020) 8:24 Page 15 of 24
Silva. Other pink and rose-coloured clusters deal with the issues of ethnic entrepreneurship, migrant networks and refugee movements. The blue cluster encompassed
both economists and sociologists who investigated economic aspects of migration and
integration/assimilation. Also, a new cluster (yellow) emerged, which we named “Acculturationists”, it is represented by authors who wrote on cross-cultural interactions, intercultural behaviour and interpersonal communication across cultures, such as
Gudykunst, Triandis, Brislin as well as J. W Berry, who became increasingly prominent
Fig. 8 co-citation networks 1985–1994 (N = 1043)
Fig. 9 co-citations 1995–2004 (N = 2237)
Levy et al. Comparative Migration Studies (2020) 8:24 Page 16 of 24
over time. This cluster seems to have a psychological disciplinary orientation and is
connected mostly with the “Race and ethnic relations” cluster.
In the late 1990s and early 2000s we found the beginning of significant
transformations in migration literature, as the reference field grew quickly (see Fig. 1).
The clusters “Acculturationists” (yellow), “Race relations” (red), “Economic sociologists”
(dark blue) seem to be positioned more closely together (Fig. 9), indicating more cocitations across these communities. “Economic sociologists” (dark blue in Figs. 8 and 9)
absorbed some authors from “Refugee studies” (violet), and “Race relations” (pink) (Fig. 8),
as the authors were co-cited more frequently. This fusion may have led to the formation of
a new cluster located next to “Economic Sociologists”, which includes Vertovec, Sassen,
Castles, and Freeman (light rosy Fig. 9). This could possibly be interpreted with the help of
our interviewees, who suggested that migration studies developed with two sociological traditions: (i) the Wisconsin/Michigan approach represented by Massey, Portes, and Cornelius,
with a focus on the migration and the (receiving) state, and (ii) the Wallerstein/world systems approach represented by Sassen, Levitt, Soysal, and Joppke which focused on globalisation and adopted a more critical ontology of assimilation and migration. We therefore
renamed the blue cluster as “Wisconsin/ Michigan school”, and the light pink as “Global
systems school”.
The new age of migration studies: 2005-present
Since 2005, a new age of migration studies has emerged. The rounder shape of the cocitation network (Fig. 10) means that there is now more literature that draws upon the authors from various clusters, pulling the edges closer to each other. Together with the diminishing citation prevalence of Caldwell’s work, the cluster of “Demographers” (green in
previous periods) has merged with part of the “Wisconsin/Michigan school” led by Massey,
Fig. 10 co-citations 2005–2014 (N = 7782)
Levy et al. Comparative Migration Studies (2020) 8:24 Page 17 of 24
Borjas and others. The cluster of the “Global systems school” has dramatically grown and
seems very intertwined with other epistemic communities. Between the yellow cluster “Acculturationists” and “Economic sociology + demography” (turquoise) we see a new cluster (Lime)
devoted to the topics of “Race, Migration and Health” represented by Williams and Krieger.
Between the “Race relations” and the “Global systems” schools we can see a cluster which
could be labelled as “Mobilities” (orange), illustrated by Sheller and Urry’s prominence.
Disciplines and cross-disciplinary osmosis
Our expert interviewees reflected in depth on the interdisciplinary evolution of the
field. In this section we bring together their perceptions and the bibliographic evidence.
Sociology was regarded as either the founding or a prominent discipline in migration
studies by nearly all our interviewees. Our findings confirm this, showing that sociology
has been one of the three core disciplines in the field since the 1970s. In Fig. 11 the
readers can see that many clusters have a sociological orientation throughout the whole
period of analysis. Moreover, since the 1990s, sociologists such as Bourdieu and
Foucault – among the most -cited authors by migration scholars (Figs. 9 and 10) –
indicate sociology’s dominance in the field.
The importance of economics in migration studies, highlighted by some interviewees,
can also be confirmed. One interviewee noted that economists have been writing on
migration since at least the 1970s, as we can observe in their separate cluster in the
period 1975–84. Another expert argued that economics joined “the talks of
globalisation and transnationalism” in 1980s, and indeed since late 1980s, the
economists were merged in one cluster with economic sociologists (dark blue)
Fig. 11 visualisation of the genesis of Migration Studies as a research field (1974–2018). Co-citation clusters
of migration studies literature 1975–2018
Levy et al. Comparative Migration Studies (2020) 8:24 Page 18 of 24
(Fig. 11), possibly due to literature referring to authors from both disciplines in
discussions on these emerging topics.
A few interviewees noted that demography has gradually become an important
discipline in migration studies. Our analysis of epistemic communities shows the
presence and prominence of demography from 1975 until 2004, after which it merged
with the cluster of economic sociology, indicating a growing shared reference basis for
quantitative migration studies in the new millennium. It is understandable that some
respondents did not consider demography a central discipline in the field. One possible
reason is that in the past demography was not at the “core” of migration studies, but it
was one of several equally prominent, yet separated “cores” until 2005. In that period,
demographic literature became increasingly co-cited with the US-centric cluster of economic sociologists and economists. This, however, is conceptually distant from the burgeoning “Global Systems school”, in which the work of the interviewee is situated.
Several interviewees agreed that lawyers and economists are not very
interdisciplinary, with few exceptions. We did not identify separate clusters of lawyers
and economists, except in the late 1970s and early 1980s, therefore this claim is not
supported by our analysis. On the contrary, economics seems to have become part of
one epistemic community comprised of economic sociologists and population studies
researchers. Though, notably, social-psychology (yellow) has maintained its separation
from other epistemic communities the longest. Surprisingly, we did not identify separate clusters of historians, despite the fact that several of our expert interviewees supported the importance of this discipline in the development of the field. This might be
due to Web of Science’s limited coverage of historically-, as well as anthropologicallyoriented journals. Even though the latter discipline was also not clearly delineated in
the co-citation analyses, quite a few social anthropologists (i.e. Pennix, Vertovec, Khosravi, etc.) were noticed among the present clusters, but they did not form a separate
group meaning that their studies have been much used by sociologists and other researchers of migration.
The cluster of social geographers began to be visible in our networks only recently
(since 2010), so according to our data it did not seem to be as important as sociology
in the field. Geographers have been perceived by our experts as the lynchpin for
interdisciplinary developments. This may be true, since we can see that their
prominence in the networks coincided with the period when the distant edges of the
network came together in the circular shape of Fig. 10.
Both qualitative and quantitative analysis of co-citation networks generally confirm
expectation 4. Overall, disciplinary orientations have not disappeared over time, but it
is clear that since the twenty-first century the co-citation network has developed a
round shape (Fig. 11), which happens when authors from very different and previouslydisconnected epistemic communities are cited together in the works of emerging
scholars. Based on this, we can confidently claim that the interdisciplinary basis for future research is now stronger than it was 40 years ago. This shift is particularly striking
from 2005 onwards. Our respondents identified the rise of transnationalism, the establishment of interdisciplinary migration research centres around the world as catalysts
for this change. This was also possibly facilitated by the creation of the interdisciplinary
funding programmes, such as the Migration Program (1994–2008) in the USA funded
by the Social Science Research Council, and the emergence of large-scale research
Levy et al. Comparative Migration Studies (2020) 8:24 Page 19 of 24
networks and postgraduate programmes at the Universities of Sussex and Oxford in
the 1990s. However, according some experts, the field is not interdisciplinary enough,
because it is hindered by existing structures (cf. Abbott 2001), namely: the higher impact factors of mainstream disciplinary journals; disciplinary boundaries in faculty
structures; and funding streams, especially those coming from the EU.
Basic quantitative analyses of the co-citation networks support our qualitative findings. The amount of unique citation sources overall increased drastically by 14 times
from the beginning of the analysed period until now. Due to this increase, the probability of two different sources being mentioned together in a study has decreased, since
there are many more authors to choose from, while the number of references in an
average scientific publication could not grow to that extent (Table 3). One would cite
30–40 sources at most per document. So, the decrease in density in this case does not
mean a disciplinary fragmentation. Looking at the average path length (APL), or the
average number of authors it takes to connect one author to another author in the network, we can see that it remained stable and has even slightly declined since the late
1990s. The APL of 2 means that on average all possible authors in the co-citation network are connected with each other via 2 other authors. In recent years this value has
become even less than 2. This means that the epistemic communities in migration
studies, despite the quantitative proliferation of the sources, remained closely interlinked. Taken together with our previous qualitative findings, this strengthens our argument that migration studies represents an institutionalised field.
Epistemic divides in migration studies
The distinction between the two sociological schools of thought (Michigan/Wisconsin
– Global systems approach) most strongly applies to the 2000s onwards. Even though
scholars from these streams have been co-cited in many studies (indicated by the close
proximity of the clusters), they still maintain their division.
One interviewee argued that there are three separate groups of migration scholars:
those focused on integration and assimilation, those studying transnational/international
migration, and another sub-field on migration and development. The first one included
scholars such as Alba, Nee, Portes, Rumbaut, Kasinitz, Waters; while the second included
Massey, Vertovec, Severs, Schneider, Soysal, Crul, and Favell. Although this interviewee
did not name specific authors in the third stream, but in the analysis, we consider authors
such as Mabogunje, Appleyard, and Castles, and, more recently, de Haas, Piper, and
Carling to be possible representatives of this group.
Our analysis largely confirms the distinction between the “integrationists” and
“transnationalists”, since the latter’s emergence in the 1990s. In 2005–2014 (Fig. 10) we
Table 3 Co-citation network density, per decade, 1975-2018
Years Total number of authors in the network density average path length
1975–1984 554 12.90% 1.97
1985–1994 1043 9.50% 2.02
1995–2004 2237 7.40% 2.00
2005–2014 7782 4.20% 1.99
2015–2018 6209 5.00% 1.98
Levy et al. Comparative Migration Studies (2020) 8:24 Page 20 of 24
see that the “integrationist” authors (Alba, Portes, Rumbaut, Kasinitz and Waters) and
interestingly also Crul, belong to the cluster called “Michigan/Wisconsin school”.
While Levitt, Vertovec, Soysal and Favell –the “transnationalists” – were part of another
cluster, “Global systems approach”. There is no conclusive evidence to suggest that the
third group, “developmental scholars”, form a “separate conversation” in any period. In
the past, authors writing on development appeared on the intersections of several
clusters, meaning that their writing was cited by scholars from multiple communities.
Moreover, the centrality and citation prominence of the UN and World Bank
references in the demographic cluster in the 1970s–1980s (Fig. 8), suggests a possible
development focus in this area. More recently, development scholars such as de Haas,
Piper, Carling, Landau have been intertwined with the “Global systems school”/
“transnationalists”, however they are somewhat separated from the integration scholars
(Fig. 10).
Key developments in migration studies
Based on the theory (E5), we expected that migration studies emerged from the
“shadows” of ethnic and racial studies in the 1970s–1990s and became its own field
after the turn of the century. Our findings indicate that throughout the whole 45-year
period studies on migration referenced both authors focused on “ethnic/race relations”
and those focused on “labour market/ economic aspects” of migrant integration. Both
streams of research grew substantially over the years (as did the field in general), with
these streams of literature gradually becoming more interlinked. The migration studies
of today did not seem to come from the shadows of ethnic/race relations studies alone,
but rather developed from a combination of demographic studies, socio-psychological
studies, race/ethnic relation studies, labour/economic integration studies, refugee studies, transnationalism and development studies.
We also expected to see the emergence of transnationalism from the mid-1990s onwards as a prominent sub-field of migration studies. This trend was suggested by several interviewees. Key authors who introduced and developed the “transnationalism”
concept include Levitt, Faist, Portes, Glick-Schiller and Vertovec. Since the early 2000s
these authors have been increasingly cited and co-cited in the migration studies, indicating a growing amount of literature looking at migration in terms of a process, not
an end point, as it was widely conceived in the 1970–1990s.
Another expectation related to the “cultural turn” of migration research, in terms of a
shift from predominantly quantitative and demographic approaches towards of
epistemic communities centred around broader qualitative studies of migration. The
reference patterns observed in the data seem to confirm such a development. The rise
and the increased citations of Foucault and Bourdieu, together with the decreased
citation significance and centrality of the Census Bureau may point to the rise of
qualitative approaches in migration studies. Although based on the co-citation analysis
we cannot claim that such approaches overtook quantitative studies, as here we analyse
reference lists of the studies, not the amount of documents and their topics. Moreover,
we notice that besides the World Bank and US census bureau, new data sources have
begun to be referenced in recent years, such as OECD, ILO, and Eurostat, Canadian
statistics, and other countries. Over 30 statistical offices are being referred to in the
Levy et al. Comparative Migration Studies (2020) 8:24 Page 21 of 24
literature in the period 2015–2018, while nearly 3 decades earlier there were only two
(US and the UK).
Conclusion and discussion: fragmentation and institutionalisation in the field
of migration studies
This article provides an empirical analysis of the growth of migration studies. It asks
whether the proliferation of migration studies over the last four decades involved a
gradual institutionalisation as a research field, or whether growth came with
fragmentation. Our analysis helps migration studies to reach beyond relatively
simplistic understandings of growth as a sign of institutionalisation in itself; it shifts
attention from the fact that migration studies has grown to how it is has grown.
We have taken self-referentiality, internationalisation and the development of cocitation networks (epistemic communities) as indicators of institutionalisation. If migration studies has institutionalised as a research field, we expected an increase in selfreferentiality, an increase of internationalisation and the evolution of a coherent set of
co-citation networks. In contrast, if growth comes with fragmentation, this would be
visible in declining self-referentiality, stagnating internationalisation and the absence of
coherent co-citation networks.
Our analysis confirms that the growth of migration studies has involved
institutionalisation as a research field. Self-referentiality has strongly increased since
the 1970s, although the data since the late 2000s suggest that this is not a linear trend.
Even when controlling for the immense increase of publication outlets (and hence
referencing opportunities), the intensity of citation links increased, especially between
1975 and 2008. Since 2008 there appears to be a stagnation, for which there is no clear
interpretation available. This could be down to lag effect in referencing, but it could
also be an indication that, since 2008, migration studies is increasingly embedded in
other fields, and develops less as a discrete research field.
In addition, we found a clear absolute and relative increase in international coauthorships. This is a clear indication of the internationalisation of the field.
Whether this indeed means that migration scholars have reached beyond the critiques of methodological nationalism requires further research. Also when compared to internationalisation in other fields, this internationalisation is also likely a
consequence of digitisation and the increase of opportunities for collaboration.
However, we also found this internationalisation to be uneven; a disproportionate
share of international co-authorships involves collaborations in (and not necessarily
between) Europe and North-America, casting a shadow on the globalisation of the
research field.
Furthermore, we found that in terms of co-citation networks, there is also a growing
coherency in the field of migration studies. Our analysis of co-citation networks shows
that whereas in the 1970s migration studies involved distinct and also very separate cocitation clusters, in the 2010s there was a clearly enhanced coherency between these
clusters. Although migration studies, as any research field, consists of distinct epistemic
communities that refer to that refer to themselves primarily, they also increasingly refer
to one and another. Many of the epistemic communities that we found also clearly relate to specific disciplinary backgrounds, such as economic sociologists, or demographers. Therefore, our findings suggest that migration studies evolved from a multiLevy et al. Comparative Migration Studies (2020) 8:24 Page 22 of 24
disciplinary field (with various but very distinct disciplines) to a more interdisciplinary
field (with various and linked disciplines).
Finally, we found distinct developments within the epistemic communities that make
up the field of migration studies. We found that migration studies does not come from
the shadows of ethnic/race relations studies alone, but rather developed from a
combination of demographic studies, socio-psychological studies, race/ethnic relation
studies, labour/economic integration studies, refugee studies, transnationalism and development studies. Furthermore, we see that recent migration studies show a proliferation of specific epistemic communities, including that on ethnic/race relations and on
global systems theory. Furthermore, new communities have emerged, such as most notably on race, migration and health.
Supplementary information
Supplementary information accompanies this paper at https://doi.org/10.1186/s40878-020-00180-7.
Additional file 1: Annex 1: Web of Science complex query. Annex 2: Yearly overview of authors, organisations,
and countries publishing migration research, 1975-2018.
Authors’ contributions
NL wrote the introduction, theoretical and methodological sections. NL conducted the analyses for and wrote the
sections on self-referentiality and internationalisation. AP cross-checked and edited all of the above sections. AP conducted the analyses for and wrote the section on epistemic communities. NL cross-checked and edited the section on
epistemic communities. PS cross-checked and edited the entire manuscript. All authors met and discussed key conclusions. PS wrote the conclusion/discussion section. NL and AP cross-checked and edited it. All authors read and approved the final manuscript.
Funding
This research is associated with the CrossMigration project, funded by the European Union’s Horizon 2020 research
and innovation programme under the grant agreement Ares (2017) 5627812–770121.
Project website: migrationresearch.com
Availability of data and materials
The bibliographic metadata are available from the corresponding author, upon reasonable request.
The data related to international co-authorships may be obtained from https://doi.org/10.7910/DVN/NNK0CQ
Competing interests
No competing interests.
Received: 6 January 2020 Accepted: 1 May 2020
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