Introduction

The recent Horizon Europe, with a budget of €95.5 billion, recently launched a Programme for Research and Innovation (2021–2027), in which international collaboration and the creation of research networks are viewed as strategic priorities to fuel scientific and technological excellence, and to strengthen the European Research Area (ERA).

Through this effort, policymakers in most European countries are focussing on promoting international research collaboration (IRC) to shape a global context of research excellence to improve the quality of research and its subsequent dissemination (Jeong et al., 2014). This implies that more than ever, the incentive and reward systems in recent European science policy are linked mainly to IRC and its effects on scientific research efficiency (Kyvik & Aksnes, 2015).

Despite IRC’s importance and influence, the reality is that some researchers are more internationalised (internationalists) than others (localists) (Kwiek, 2020). Whether a researcher’s stronger internationalisation is associated positively with higher publication rates, greater visibility and/or heavier impact from generated knowledge, why do some researchers collaborate more internationally than others?

Internationalisation confers greater prestige on the researcher and even has the capacity to be a stratifying force in the scientific profession (Kwiek, 2020). Academics who do not collaborate internationally may expose themselves to cumulative disadvantages in terms of greater difficulty accessing resources, generating research visibility and/or attaining academic prestige. So why not collaborate internationally?

Furthermore, such differences between researchers’ international collaboration patterns also stem from the scientific field in which they work (Aksnes et al., 2019; Kwiek, 2020). In particular, notable dissimilarities have been found between science, technology, engineering and mathematics (STEM) research and social sciences, humanities and arts (SSH) (Olmos-Peñuela et al., 2014). However, extant literature mainly has focussed on comparative analyses concerning different scientific fields’ internationalisation levels (Kwiek, 2015, 2020; Kyvik & Aksnes, 2015), while less attention has been paid to determinants that generate differences. Therefore, to clarify this dimension in the IRC context, we wondered about factors that explain differences between researchers’ IRC behaviours and levels. Are they personal traits, institutional support, individual preferences, etc.?

To shed some more light on the question, this study aimed to identify determinants that influence IRC levels. Although we can consider that the decision to internationalise is ultimately a personal one, the literature suggests that two broad sets of individual and collective factors shape and may even determine this academic behaviour (Blackburn & Lawrence, 1995; Finkelstein et al., 2013; Porter & Umbach, 2001). In this vein, the decision to collaborate internationally will be assumed to be an academic’s choice formed by individual factors tied to the researcher and collective factors tied to their scientific teams:

  • From the individual perspective, internationalisation level has two antecedents: (1) the researcher’s motivation and predilection toward scientific research; and (2) the researcher’s attractiveness (human capital) to international colleagues (Finkelstein et al., 2013).

  • From the collective perspective, as it is well-recognised in the literature nowadays, scientific research is characterised by a system of generating knowledge that is “socially distributed” (Hessels & Van Lente, 2008). Therefore, scientific teams are viewed as the ideal context through which to generate and accumulate scientific knowledge (Hautala & Jauhiainen, 2014; Murayama et al., 2015). Thus, we suggest that certain determinants within the scientific team may help establish greater contacts with international colleagues, in particular, 1) the social capital level of the scientific team to which the researcher belongs, 2) the principal investigator’s (PI) leadership style and/or 3) the scientific team’s productivity level are contextual factors that also may influence the researcher’s decision to facilitate international collaborations.

Based on the factors mentioned above, this paper aims to address the following research questions:

  1. (I)

    To what extent do individual or collective factors determine academic researchers’ decisions to collaborate internationally?

  2. (II)

    Do disciplines of science exhibit significant differences in the factors that explain the researchers’ IRC behaviours and levels?

Therefore, the objective of this study is to enhance the understanding of those “internationalist” academics by analyzing the individual and collective determinants that influence levels of international research collaboration in STEM and SSH sciences.

Based on a large-scale academic survey (N = 954), this paper offers significant implications for the study of academic careers and scientific performance, contributing to a deeper understanding of the patterns governing international collaboration. The findings presented can guide university policies to promote the internationalization of research.

The paper is structured as follows. First, we explain the theoretical arguments used to establish the hypotheses tested in this study. Subsequently, we empirically test our hypotheses based on a sample of 954 Spanish academics using hierarchical multiple regression analysis. Finally, we discuss our findings and draw conclusions from this study.

Theoretical framework

International research collaboration

Numerous studies have reported exponential growth in the number of papers published with international coauthorship (Abramo et al., 2011; Nguyen et al., 2017; Dusdal & Powell, 2021). The degree of researchers, scientific teams and universities’ openness towards international collaborations is increasingly relevant to accumulation of human capital and scientific competitiveness (Aldieri et al., 2020). Today, it is difficult for a researcher to remain isolated from collaborations with international colleagues, as science has become a more specialised, global and collaborative academic realm. However, the exponential growth of IRC has also led to a greater development in its study, capturing the attention of multiple authors (Kwiek, 2018, 2020; 2021; Dusdal & Powell, 2021). In a recent literature review, Chen et al. (2019) identify three main stages in the last 50 years of study of IRC: “emergence” (1957–1991), “fermentation” (1992–2005) and “take-off” (2006–2015). Therefore, it could be said, as recent literature argues, that there has been an explosion of such investigations currently (Chen et al., 2019; Vieira et al., 2022).

Scientific collaboration is a matter of social convention among scientists, defined by extreme complexity in its conceptualisation, so it can be described in many different ways (Katz & Martin, 1997; Kwiek, 2020). According to Laudel (2002, p. 5), research collaboration can be conceived as a ‘system of research activities by several actors related in a functional way and coordinated to attain a research goal corresponding with these actors’ research goals or interests’. For Kwiek (2020, p. 59), IRC can be defined as ‘an emergent, self-organising, networked system, in which the selection of partners and research settings often relies on the researchers themselves’. IRC provides the greatest ‘attractiveness, international visibility and, often, it implies a significant commitment on the part of the researcher’ (Smeby & Gornitzka, 2008, p. 48). Therefore, assuming a perspective based on research results, IRC can be conceived as a self-organised and networked system in which researchers select specific international research partners and environments for functional development of research to obtain superior research results.

Importance of international research collaboration

Multiple studies have reported exponential IRC growth in recent decades in different fields of knowledge (Adams, 2013; Wagner et al., 2015; Kwiek, 2020; Dusdal & Powell, 2021). For example, Wagner et al. (2015) found that internationally coauthored publications increased from 10.1% in 1990 to 24.6% in 2011. This increasingly international research environment appears to be a new defining characteristic of global science (Kwiek, 2020). As some studies have argued, this IRC growth is supported by the generalised conception that science should be recognised as internationally relevant and as one of the classic principles of peer review (Woldegiyorgis et al., 2018). Furthermore, the very complexity of today’s great social challenges goes beyond the intellectual capacity of any one institution or scientific team, making it necessary to combine knowledge and resources beyond national borders (Keenan et al., 2012).

Clearly, the orientation today leans towards international collaboration in the approach to incentive and reward systems in recent European scientific fields (Kyvik & Aksnes, 2015). Policymakers in most European countries and the European Union itself have encouraged IRC through the philosophy that it creates a global context of research excellence that improves the quality of research and its subsequent dissemination (Jeong et al., 2014). This places increasing pressure on European researchers to pursue international collaboration if they intend to access research funding for projects (Kwiek, 2020). Over the past two decades, most European Union (EU) research project funding programmes and international mobility programmes have encouraged IRC (Kwiek, 2018). Access to EU funding sources in most cases favours applications in which members of the research project come from at least three different countries, and the criteria usually benefit PIs with extensive international research networks and experience in mobility (Kwiek, 2020). But, in addition to individual incentive systems, the growth of IRC is also attributed to the prevailing university prestige maximization system derived from the internationally recognized criteria found in rankings like the Shanghai Ranking (Academic Ranking of World Universities), or the Times Higher Education World University Ranking (THE). It is evident that, while scientists enhance their individual prestige by collaborating with top researchers in a field of knowledge, they also maximize the prestige of the institutions to which they belong (Kwiek, 2020).

International research collaboration and research productivity

Myriad studies in the literature have focussed on studying IRC’s effect on scientific productivity and its impact on investigations. The logic behind these studies is based on the idea that IRC is a powerful tool for fostering scientific and technological advances through greater individual productivity among researchers (measured by the number of publications with international co-authorship) and greater scientific impact (measured by the number of citations) (Abramo et al., 2011; Katz & Martin, 1997; Kwiek, 2016, 2020). For example, Abramo et al. (2011) found a positive correlation between publications with international co-authorship and individual research performance in their study on Italian academics, which in turn influences the subsequent impact of these publications. Similarly, Kwiek (2016) concluded that the most significant predictor of scientific productivity of highly productive academics in Europe was the levels of international co-authorship they had developed during their academic careers. Therefore, although there may not always be a causal relationship between scientific productivity, it is clear that highly productive scientists tend to collaborate with international colleagues to a greater extent (Kwiek, 2018). The cultural diversity characterizing international collaborations could foster a higher level of creativity in research development, affecting its quality and impact (Wagner et al., 2019). In fact, multiple studies have revealed that researchers who publish with international colleagues achieve greater visibility of their published research, which in turn benefits the number of citations obtained (Glänzel & Schubert, 2001; Gazni et al., 2012; Adams, 2013; Dusdal & Powell, 2021).

Therefore, based on these considerations, researchers are expected to develop a more ‘internationalist’ attitude than ‘localist’ researchers, who only have local research as a frame of reference (Kwiek, 2015, 2018). However, the reality is that some researchers are more internationalised than others (Kwiek, 2020). So, then, as posed earlier, why do some researchers collaborate more internationally than others?

Driving factors of IRC: individual and collective determinants

Reviewing the literature, a set of studies identify multiple antecedents that influence the development of IRC (Abramo et al., 2013; Dua et al., 2023; Kwiek, 2018; Kyvik & Aksnes, 2015; Vieira et al., 2022). However, due to the large number of studies that have analysed the different determinants of IRC, the literature is, to a greater extent, dispersed. In this sense, Kwiek (2020) proposes that the more specialized IRC literature can be classified into three main topics: (i) macro-level factors (country characteristics, reward structures, scientific fields, or the geographical distance); (ii) organizational or collective factors (reputation or available resources); and (iii) individual factors (gender, motivation or age).

Considering the different nature of potential factors, in this paper, we based our study on a socio-collective perspective to address the literature gap on determinant affecting IRC (Blackburn & Lawrence, 1995; Finkelstein et al., 2013; Porter & Umbach, 2001). This approach offers an integrative approach that combines individual and collective factors in scientific research to understand the determinants of IRC. The decision to collaborate internationally with other colleagues is presupposed as a decision in which researchers decide on the best way to allocate their limited resources (Kwiek, 2020). This decision obviously will involve various potential benefits, e.g., access to unknown knowledge and experiences, or increased scientific productivity (Kwiek, 2018, 2020). However, this study conceptualises internationalisation as a researcher’s decision shaped by two broad sets of individual and collective factors (Blackburn & Lawrence, 1995; Finkelstein et al., 2013; Porter & Umbach, 2001). This approach aligns with the defining environment of scientific research today, in which work is fundamentally social, and research is conducted through scientific teams (Lee & Bozeman, 2005; Zheng, 2010). As the socio-collective perspective posits, the joint consideration of individual and collective factors that reciprocally influence the researcher’s decision to internationalise means that the present study is based on the precepts established by social cognitive theory (Bandura, 1978), according to which, human behaviour and decisions are conditioned by personal cognitive and behavioural factors, along with other environmental factors. Therefore, the aforementioned arguments provide the necessary theoretical basis through which to classify determinants of IRC conceptually from a dual individual and collective perspective to discuss this study’s hypotheses.

From the individual perspective, it could be argued that IRC may be conditioned by researchers’ motivation level and attractiveness (human capital) to other international colleagues. A greater interest in science and gaining recognition among peers underpin the motivation behind the ‘sacred spark’ hypothesis (Cole & Cole, 1973). This strong motivation to persist in the pursuit of long-term research goals leads them to collaborate internationally to obtain higher rates of scientific productivity and greater peer recognition. Similarly, a researcher has limited cognitive capacities and rationality, so collaboration is viewed as a key element that can provide greater scientific impact (Bozeman et al., 2013; Li et al., 2013; Liao, 2011). Therefore, the ability to join international research networks also will depend on the attractiveness of one’s cognitive abilities and competencies as a researcher to international peers (Wagner & Leydesdorff, 2005). As Kyvik and Larsen (1994, p. 163) noted, ‘Visibility is a basic condition for being potentially interesting to other scientists, but one also has to be attractive in order to be actively sought out by others’.

From a collective perspective, we also viewed a scientific team’s work environment as a relevant determinant of IRC. In this sense, the influence that the working environment and relationships with other team members or team management experts on the researcher can enhance and facilitate international relations with other colleagues. The literature already has demonstrated how reputation, visibility or the ability to work in the researcher’s organisational environment can impact the researcher’s individual performance positively (Allison & Long, 1990; Baloch et al., 2021). Environmental theories support the conditions in which research currently is conducted, which are more conducive to teamwork and common effort than working alone.

Hypotheses

Determinants of IRC: individual factors

Human capital and IRC

In an integrative way, by applying the ‘KSAs’ framework, human capital is understood as individuals’ knowledge, skills and abilities (De Frutos-Belizón et al., 2020; García-Carbonell et al., 2021; Nyberg & Wright, 2015). In the academic context, scientists can seek complementarities to their scientific knowledge (K) through collaborations to develop new approaches, methodologies and research ideas. Normally, researchers who master knowledge in particular scientific fields obtain better results and make a greater impact in these fields (De Frutos-Belizón et al., 2020; Jacob & Lefgren, 2011). However, skills (S) have a more generic character and are related to better performance of research tasks (De Frutos-Belizón et al., 2020). These ‘soft skills’ also are linked to better research productivity and refer to communicative and idiomatic skills, research management capabilities, creative skills or teamwork skills (McNie et al., 2016). The incorporation of scientists who are proficient in these relevant skills is viewed as important in the collaborative environments in which research occurs (Dusdal & Powell, 2021). Finally, the researchers’ abilities (A) relate to the individual’s capacity to conduct research correctly (Lindberg & Rantatalo, 2015). Therefore, unlike skills, abilities, i.e., ‘hard skills’, have a specific character in the development of scientific tasks (McNie et al., 2016). In this sense, those who have analytical reasoning abilities, can formulate hypotheses or can disseminate research results possess competencies for generating scientific productivity (Thunnissen & Van Arensbergen, 2015; Ulrich & Dash, 2013).

Therefore, based on the aforementioned arguments that define the researcher’s human capital, the initial assumption is that these researchers’ individual attributes function as the origin of research collaborations (Abramo et al., 2017; De Frutos-Belizón et al., 2023). As Kwiek (2020) argued, IRC depends, to a greater extent, on individual scientists’ ‘power’. These arguments are consistent with the idea that IRC allows researchers to seek complementarities in other scientific colleagues with respect to their human capital with the aim of achieving balanced attributes in all dimensions of human capital (De Frutos-Belizón et al., 2023; Kwiek, 2018). Therefore, based on this rationale, scientists who possess better human capital are going to be more visible and ‘attractive’ to other colleagues in their scientific fields, i.e., a scientist who possesses more extensive knowledge in a particular subject will arouse greater interest in their scientific community to establish scientific collaborations. For example, a scientist who has specific knowledge in a particular methodology will have high visibility within their field, which either will lead to them receiving multiple proposals to collaborate, or colleagues will access this scientist’s publications to seek out this specific knowledge in conducting their own research.

Therefore, the argumentation behind Hypothesis 1 is that researchers who possess greater human capital tend to be more productive and visible in their scientific fields. This superior knowledge and set of competencies allow them to gain greater ‘attractiveness’ among their scientific peers, so that we can expect them to collaborate internationally to a greater extent. Thus, we propose:

Hypothesis 1

The researcher’s human capital positively influences the level of international research collaborations.

Motivation and IRC

Regarding the second individual factor, a substantial body of literature has examined academic researchers’ motivation. Studies such as Yemini (2021) have found that IRC is part of research activity that generates new knowledge and social relations. Likewise, some previous studies have proposed that research motivation is crucial for the emergence of IRC (Kwiek, 2018, 2021; Kyvik & Larsen, 1994), as well as every stage of researchers’ careers (Hangel & Schmidt-Pfister, 2017). However, the relationship between motivation and IRC has not been examined in depth in the literature, as well as the effects that it elicits.

Traditionally, research motivation has been considered from two perspectives: intrinsic and extrinsic motivation. Intrinsic motivation emphasises academics’ passion for or satisfaction with academic research because of the interest generated by understanding the complex nature of research (Ryan & Deci, 2000). However, extrinsic motivation focusses on external rewards from doing research, which are related to passive compliance (Ryan & Deci, 2000). Academic researchers should embrace both types of motivation to elicit exponential results from research activities (Guerrero-Alba et al., 2021; Peng & Gao, 2019).

However, the literature postulates that the motivation that exerts the greatest effect on researchers’ performance is intrinsic motivation (Stupnisky et al., 2019, 2023). A researcher, based on the principles of science, wants their research to make a greater societal impact. In this sense, the literature has demonstrated that internationally coauthored papers make a greater impact than nationally coauthored papers (Oh et al., 2010). Furthermore, researchers who obtain greater prestige in their scientific communities also develop stronger vocational feelings towards obtaining greater international visibility. Furthermore, previous literature has pointed out that status, reflected in prestige and academic position, is a determining factor in the establishment of international collaborations (Acedo et al., 2006; Jeong et al., 2014).

Some studies have highlighted that IRC’s focus on incentives aims to establish new research opportunities, additional resources, training of researchers or increased research strength and status (Shih & Forsberg, 2023; Wagner & Leydesdorff, 2005). Different studies have highlighted that universities propose specific funding lines for researchers to collaborate with other international institutions (Kienast, 2023). Researchers should take advantage of these incentives to establish more efficient international relations, which foster joint research interest. These incentives would lead to IRC and the purchase of expensive equipment (Melin, 2000) to help obtain better research results, thereby fulfilling promotion requirements at their universities (Kim & Bak, 2017).

Based on these aforementioned arguments, we propose the following hypothesis:

Hypothesis 2

Researchers’ motivation (intrinsic and extrinsic) positively influences the level of international research collaborations.

Determinants of IRC: collective factors

Social capital and IRC

The concept of social capital is accepted widely in the literature as a construct grouped into three interrelated dimensions––structural, relational and cognitive––derived from the network of established relationships (Martín-Alcázar et al., 2019; Nahapiet & Ghoshal, 1998). This social network contributes to the generation and exchange of knowledge. The structural dimension refers to the patterns of connections between a social network’s members. The larger the network of contacts established by the scientific team, the greater the possibilities for accessing research networks and establishing connections with other colleagues. The relational dimension refers primarily to trust, behavioural norms, social climate, obligations and expectations, as well as the identification created through personal relationships between actors (Nahapiet & Ghoshal, 1998). The team climate and trust between team members will enable social exchange and collaboration, which are conducive to knowledge sharing and team performance. Solid and frequent social interaction allows actors to get to know each other better, share information and ideas, and, thus, impact mutual trust (Martín-Alcázar et al., 2019). Finally, the cognitive dimension refers to those resources that favour the communication and combination of knowledge. On the scientific team, the transfer of knowledge, ideas and contacts allows members to access more information and a larger network of contacts, which could help establish new external collaborations.

Therefore, based on the previous considerations, we consider that the scientific team’s social capital is one of the collective factors that can make the greatest impact on the establishment of IRC. Hsu and Hung (2013) argued that the existence of trust within the group improves the capacity for knowledge integration among group members, positively influencing willingness to share knowledge, information and contacts. Similarly, a cohesive climate of mutual trust is viewed as a central condition for establishing collaborations, allowing the team’s principal investigator to take (social or epistemic) risks in develo** scientific collaborations (Hückstädt, 2023; O’Rourke et al., 2019). However, a high configuration of social capital within the scientific team benefits more than just the exchange or generation of scientific knowledge. As Burt (1997) noted, models need to consider social capital’s benefits at the individual level, emphasising benefits that individuals extract from their networks of formal and informal relations with other academics. In this sense, the literature has demonstrated how social capital facilitates access to broader sources of information and improves information quality, relevance and timeliness (Bozeman et al., 2013; Gonzalez-Brambila et al., 2013; Liao, 2011). This all positively affects team members’ productivity and research impact (De Frutos et al., 2020), leading to greater visibility in the scientific community and, consequently, more opportunities to collaborate with other colleagues. Therefore, based on these arguments, we propose:

Hypothesis 3

A high level of social capital within a scientific team positively influences the level of international research collaborations.

Team leadership and IRC

Bland et al. (2005) concluded that group productivity is affected by institutional and leadership characteristics the most (Shih & Forsberg, 2023; Zhang et al., 2023). In this vein, PIs’ role within research teams is crucial to explaining their performance (Harvey et al., 2002). Regarding the latter, the leader’s role provides pioneering and innovative guidance, as well as new trends in the discipline itself, by recognising the implications of the research they develop within the group. In this sense, the search for the optimal leadership style to achieve the desired team outcomes has been a recurring theme among researchers to explain individual and group performance (Zhao et al., 2019). In this research, we consider that the leadership style that best suits research teams’ needs is knowledge-oriented––the best type to explain IRC behaviour (Ballesteros-Rodriguez et al., 2022; Donate & Sánchez de Pablo, 2015).

Thus, knowledge-oriented leadership in particular can be understood as the leader’s behaviour in supporting the other members of the group in learning processes by giving them freedom over the progress of the research in achieving the research team’s goals (Zhang & Cheng, 2015).

This leadership style is appropriate for collaboration, as it allows for fostering coordination, providing necessary resources and collaborating jointly among participants (Yukl, 2012). Therefore, based on their arguments, we propose:

Hypothesis 4

Knowledge-oriented leadership positively influences international research collaboration.

Team scientific productivity and IRC

Our final hypothesis aimed to examine how working dynamics influence the researcher’s ability to establish IRCs. To do so, we referred to the working atmosphere as a proxy that refers to the dynamics or rhythm of a scientific team’s work. These research-oriented work dynamics, characterised by high levels of productivity, contribute to an atmosphere of collaboration and work that favours IRC (Anderson et al., 2000; Hückstädt, 2023). Therefore, work atmosphere refers to the scientific productivity that the group can develop, i.e., the scientific team’s strict research orientation and its level of work. Research-oriented teams with higher scientific performance maintain an active role in research through a cohesive collaborative climate that encourages debate and discussion, generating the free exchange of scientific ideas (Hall et al., 2012). Similarly, a highly productive scientific team can contribute to the constructive resolution of research objectives (Cooke & Hilton, 2015). Highly research-active scientific team members make their own human capital available to their team, but also their own relationships with other colleagues. This allows for access to all scientific team members’ scientific networks, which can help develop new international collaborations.

Therefore, we propose that these researchers who belong to highly research-oriented scientific teams with high scientific productivity can benefit from contacts established within that scientific team. Furthermore, researchers on highly productive scientific teams are also highly internationalist researchers. Extant literature has analysed this effect at the individual level. Although the direct relationship between productivity and collaboration levels is not necessarily causal, the reality is that the most productive scientists are more internationally visible and potentially more attractive to the scientific community (Kwiek, 2020). Abramo et al. (2011) found that these scientific outputs’ quality and productivity levels are related positively to international collaboration levels. Therefore, scientists with higher productivity levels generally tend to establish more international collaborations than their peers with less scientific output (Kwiek, 2018). Based on these arguments, we propose:

Hypothesis 5

Being a member of a scientific team with high productivity levels positively influences the establishment of international research collaborations.

Methodology

Survey design

The initial data necessary to test the hypotheses were collected through a research questionnaire sent to academic researchers from Spanish public universities. To collect data among the academic researchers, the collaboration of the vice rectorates for research of the Spanish public universities was requested. Through an email, a link to the online survey on the SurveyMonkey® platform was distributed. This platform allowed us to keep track of the submissions and responses from the respondents.

The first mailing process generated 1174 preliminary responses. Subsequently, a second mailing process with a reminder generated 1558 preliminary valid responses.

However, to define the final sample, we implemented a filtering process on the preliminary responses. In line with the study’s objectives, the first filter was applied to select respondents who held academic positions involved in research activities (full professor, professor, associate professor, assistant professor, post-doctoral researchers, and pre-doctoral researchers). Similarly, a second filter extracted the responses of those respondents who identified themselves by name or ORCID, what helped us to collect their publication records and details on their international collaborations. Finally, after this filtering process, the study was based on a final sample of 954 academic researchers from Spanish public universities. Table 1 includes descriptive data regarding the composition of the final sample.

Table 1 Descriptive statistics
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Measures

Based on the extant literature on the methods used to value research, one dependent variable, IRC (Y), was chosen. This measure was obtained from each academic researcher’s SciVal database in the sample. SciVal provides access to research outputs of research institutions and their affiliated researchers, allowing us to measure the international collaborations of our sample. According to Scival, this measure of international collaboration indicates the extent to which an academic’s publications are co-authored with researchers affiliated with institutions in other countries. This approach understands international collaboration as joint scientific results obtained through international co-authorship of scientific publications (Adams, 2013; Kwiek, 2020).

Also, on the basis of the literature analysed and the hypotheses presented above, IRCs’ dependence on the following independent variables was analysed:

  1. (1)

    Academic human capital (X1): H1 was formulated to confirm the possible positive effect of academic human capital’s presence on IRC. We used a validated scale on academic human capital by García-Carbonell et al. (2021).

  2. (2)

    Academic social capital (X2): H2 was formulated to verify the possible positive effect of the presence of academic social capital on IRC. In this case, we used a validated scale on academic social capital by De Frutos-Belizón et al. (2021).

  3. (3)

    Knowledge-oriented leadership (X3): H3 was formulated to verify the existence of a positive relationship between the perception of leadership and IRC. In this case, we used a validated scale on academic social capital by Ballesteros-Rodríguez et al. (2022) and Donate and Guadamillas (2011).

  4. (4)

    Academic Research motivation (X4): H4 was formulated to verify the existence of a positive relationship between (intrinsic and extrinsic) academic research motivation and IRC. To study this relationship, we used Guerrero-Alba et al.’s (2021) academic research motivation validated scale

  5. (5)

    Index of scientific team (X5): H5 was formulated to verify the existence of a positive relationship between the team H5-Index and IRC. In this case, we used the measure provided in SciVal for each of the scientific teams to which the researchers belonged. This measure reflects the scientific team’s productivity and scientific impact over a specific 5-year period.

Empirical analysis

The empirical analysis was developed through two main stages. First, (i) we conducted a factor analysis to identify the implicit dimensions of both, individual and collective components, of the data: academic human capital; academic social capital; knowledge-oriented leadership; and research motivation. Since these variables were extracted through validated measurement scales, it was necessary to confirm the factorial structure of the data obtained. The analysis was based on the main-components method of extraction, resulting later in a varimax rotated solution. Kaiser–Meyer–Olkin and Bartlett’s sphericity tests were conducted on the four factor analyses. The decision regarding the number of factors was based on the screen test (Cattell, 1966) and on the eigenvalue selection criterion being superior to the unit (Kaiser, 1974). Items that did not load adequately on their factors were eliminated, then the test was repeated.

Secondly, to test the hypotheses, a (ii) hierarchical multiple regression analysis was conducted using SPSS (Version 21). This analysis was conducted to study the relationships between the dependent variables (Y), defined by the academic researchers’ IRCs, and the independent variables (X), defined by academic human capital, academic social capital, knowledge-oriented leadership, research motivation and the research group’s H5-Index. We specifically chose hierarchical multiple regression analysis as it allows us to establish a fixed order of entry for variables in order to test the individual direct effects of each of the independent variables of the study separately.

Results

Table 2 presents the aforementioned variables’ impact on IRC. Models 1 and 2 present the control and direct variables’ effects on IRC. In particular, as observed in Table 2, only gender and academic rank, as control variables, indicated significant effects (negative and positive, respectively). Model 2 indicates that direct relations exert varying and significant influence on IRC, as follows (Table 3):

  • Human capital (only the H1 dimension, research abilities) exerted a relatively weak and positive effect in Model 2, ‘All Fields of Knowledge’ [β = 0,065 (p < 0.05) and β = 0.095 (p < 0.1)] for the SSH field, partially supporting Hypothesis 1.

  • Motivation

    1. o

      Extrinsic motivation exerted a relatively negative and weak effect [β =  − 0.056 (p < 0.1) and β =  − 0.076 (p < 0.1)] on the STEM field.

    2. o

      Intrinsic motivation exerted a weak, but positive, effect [β = 0.069 (p < 0.05)] (all fields), for STEM [β = 0.092 (p < 0.05)] and for SSH [β = 0.088 (p < 0.1)].

Both of these results partially support Hypothesis 2.

Table 2 Results of the regression analysis
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Table 3 Implications of regression models for hypotheses testing
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  • Social capital: In two of the proposed models (all fields and STEM), social capital’s relational dimension was positive and significant (β = 0.079; p < 0.05 and β = 0.107; p < 0.05). Something similar happened to social capital’s structural dimension, indicating a stronger effect [β = 0.143 (p < 0.01) and β = 0.181 (p < 0.01)], partially supporting Hypothesis 3.

  • Knowledge-oriented leadership: For this variable, only the SSH model indicated a very low and negative effect (β =  − 0.006; p < 0.05), which, in practice, does not indicate enough support for the hypothesis 4.

  • H5-Index of the scientific team: in this variable, the effects seemed to be more relevant in all the tested models for STEM [β = 0.353 (p < 0.01) and β = 0.294 (p < 0.01)] and SSH [β = 0.449 (p < 0.01)], supporting Hypothesis 5.

Table 3 provides a summary of the hypotheses that were confirmed, partially confirmed, or rejected.

Discussion

This article aimed to identify the factors that explain why some researchers collaborate more internationally than others, starting with Finkelstein et al.’s (2013) approximation that proposes the integrative analysis of individuals and collective factors. Our findings indicate that collective factors (social capital and the H5-Index of the scientific team) exert a greater effect on determining IRC levels than individual factors (human capital, motivation and leadership). In particular, one of the most surprising results is related to the study’s human capital dimension. Contrary to our expectations, academic human capital does not exert an important influence. As mentioned earlier, only research abilities exert a weak effect on the SSH model. In our sample, researchers’ human capital does not seem to be the origin of research collaborations (Abramo et al., 2017). Thus, being more ‘attractive’ as a researcher to other international colleagues (Finkelstein et al., 2013) is not a clear determinant of IRC levels. Furthermore, as the results suggest, other researchers can view team productivity (as measured by the team H5-Index) as the real ‘attractiveness’ to justify collaboration more than a set of individual attributes. In essence, attributes do not ensure successful IRC per se; however, being a productive team may be an antecedent for relevant and fruitful collaborations (Kwiek, 2016, 2020). As our findings reveal, the H5-index is strong and significant in all the tested models, as the most influential variable in the regression. It is possible that researchers who search for collaborators pay particular attention to how productive research teams are, e.g., by considering number of publications, because it is much easier and more tangible than trying to value researchers’ human capital.

Something similar happens to researchers’ motivation. Despite a large amount of the literature explaining that motivation is a key element in researchers’ decisions and activities, including IRC emergence (Kwiek, 2021), our results indicate only a slight effect from this individual aspect. As explained, intrinsic motivation can be viewed as a driver of the extent to which a researcher collaborates internationally, although its influence is not strong. In this sense, status and prestige, having intellectual challenges and academic position (Jeong et al., 2014), can be viewed as antecedents of IRC. However, extrinsic motivation (i.e., extra rewards) exerts a negative and even weaker effect. It can be understood that this kind of motive may hinder international collaboration. Furthermore, as Ryan (2014) posited, intrinsic motivation exerts more influence as a determinant of scientific productivity than extrinsic motivation, with the latter negatively correlated with research productivity (Horodnic & Zait, 2015). It can be explained because ‘academics may be more intrinsically motivated to do research because they view research as a vocation’ (Ballesteros-Rodríguez et al., 2022, p. 213).

Another interesting finding related to individual factors refers to the knowledge-oriented leadership effect. We expected that PIs, as team leaders, would foster coordination, provide resources and collaborate (Yukl, 2012). However, and surprisingly, this variable’s effect is negative and very weak, only appearing in the SSH model (β =  − 0.006; p < 0.05).

Conclusions

As mentioned in the introduction, a number of studies has mainly focused on comparing the development of international collaborations across different disciplines (Kwiek, 2020; Kyvik & Aksnes, 2015). However, less attention has been paid to the antecedents that could explain these differences. In this vein, the novelty of the study rests on the joint analysis of micro-level factors—individual and collective—as potential antecedents that affect IRC levels in STEM and SSH fields of knowledge.

Considering the mentioned findings, it can be concluded that in a way, individual factors––e.g., human capital and motivation, and even leadership––seem to be insufficient for establishing international connections to collaborate, i.e., a potential collaborator may have outstanding abilities as a star researcher or demonstrate deep motivation to collaborate, but according to our results, more complex aspects are needed to develop efficient and productive IRC. In this vein, subsequent findings will reinforce the aforementioned idea because, as explained above, the most relevant and influential variables in our models are social capital and team productivity (H5-Index).

Regarding social capital, it is, by definition, necessary ‘infrastructure’ to facilitate the generation and exchange of knowledge because it implies the existence of a network derived from a number of established relationships (Martín-Alcázar et al., 2019). In this sense, social capital appears to be a significant and relatively strong influence in two of the tested models (all fields of knowledge and STEM). Concretely, social capital’s cognitive and structural dimensions seem to be the most influential aspects in promoting IRC. These findings are coherent with the extant literature because as defined, the cognitive dimension’s social capital relates to resources that favour communication and knowledge exchange as values, languages or codes (Chow & Chan, 2008). In this vein, it can be logical that a higher level of social capital in its cognitive dimension may improve the level of international contacts in research. Furthermore, as the models indicate, social capital’s structural dimension is even more important than the previous one in generating international collaboration. Furthermore, it makes sense because structural social capital refers to the patterns of connections between members of a social network––centrality, strength of connections, network size and structural holes (Zheng, 2010). The greater the number of contacts from the scientific team, the better the options to access and create connections with other colleagues, including international researchers. As Filieri et al., (2014, p. 431) explained, ‘Structural social capital facilitates the flow of information, it enables influence on network members, it certifies the network members’ social credentials, reflecting (the) ability to access resources via social relationships, and it reinforces identity and aids recognition as a social group member who shares similar interests and resources as other members’ (Lin, 2001). In this respect, having shared, realistic and clear goals in a network, and promoting interdisciplinary communication to better understand different research works and knowledge are important factors that influence collaborations (Hückstadt, 2023). In particular, social capital’s most relevant effect appears in the STEM model, which fits the publication pattern in these areas that traditionally display higher coauthorship levels (Gazni et al., 2012).

In relation to the team H5-Index, as explained above, it can be understood that being a productive team may attract potential collaborators more than human capital attributes that, though important, are not tangible, nor a guarantee of success.

Finally, contrary to our expectations, we did not find important differences between types of knowledge areas regarding the studied variables. In actuality, the results reveal that in both areas, SSH and STEM, collective factors play a more primary role in promoting IRC than individual ones. The logic behind this could be that although individual aspects may exert a certain influence, collective items seem to create the basis on which networks are built, fulfilling a double condition: 1) team productivity to lure potential collaborators and 2) team social capital as the origin of new contacts.

Practical implications

Through this study’s findings, some interesting conclusions can be drawn that inspire diverse practical implications for the design and implementation of academic staff management policies at universities. In essence, we suggest focussing on the development of individual researchers and teams’ social capital and network ties. Our logic rests on Melkers and Kiopa’s (2010, p. 391) idea that ‘researchers must have some level of established social capital that allows them to interact effectively within the international collaborative environment’. In this sense, collaborations should be systematised to make them more accessible to most researchers and teams, and research networks should be strengthened and established (Kyvik & Reymert, 2017).

Thus, on an individual level, it is crucial that researchers sufficiently develop their social capital to feed their team networks (Melkers & Kiopa, 2010). In practice, training oriented toward develo** researchers’ English language and/or communication skills could help expand potential collaborations beyond personal connections. Furthermore, as IRC is viewed as a time-consuming activity, other actions should be designed to reduce teaching credits or increase sabbatical periods (de Frutos Belizón et al., 2023).

Promoting scientific mobility also would foster the creation of new ties and networks, as well as it could help to maintain existing ones. In this sense, mobility could complement extant initiatives (e.g., Marie Skłodowska-Curie or Erasmus Programme) that involve signing collaboration agreements with universities, searching for essential resources (data or equipment) or working on particular research interests or teams. From this mobility, the networks may function as ‘conduits of knowledge’ (Turpin et al., 2008), leveraging information, expertise and knowledge ‘at a distance’ (Woolley et al., 2008).

Social capital and research networks also can be promoted by increasing research teams’ visibility. Due to the team H5-Index’s importance in our regression models, as one of the main IRC determinants, fostering research teams’ visibility could be useful in demonstrating the team’s academic status, as well as cultivating potential contacts and collaborators (e.g., research teams or researcher websites hosted on universities’ websites). Through this, researchers could follow fellow teams/researchers’ work more closely, including funded projects, recent publications or research interests, fostering interdisciplinary communication that can cultivate collaborations (Hückelstat, 2023).

Limitations and future research directions

In any case, the findings should be considered with caution because the study contains several limitations. First, the research used only a Spanish sample, which may hinder the results’ generalisability. A future research direction could be to examine other national contexts, then compare the data from various countries and research systems. Furthermore, the data came from a particular point in time, and longitudinal studies can be conducted to seek broader information about the causality between variables. Regarding the studied variables, it could be interesting to test different types of leadership apart from knowledge-oriented leadership. As Hückelstat (2023) noted, among others, PIs and their characteristics may be determinants in research collaboration success. Therefore, more research is needed in this realm. Apart from leadership, other conditioning factors should be examined more thoroughly, e.g., universities’ academic status and research teams from other disciplines that may be better prepared to develop IRC. Another limitation of the study could be that it focuses mainly on individual-centered factors without exploring other dimensions such as proximity. Future studies could deepen the combined effects of other determinants of IRC related to geographical, socioeconomic, political, or cultural dimensions (Vieira et al., 2022).

Finally, it would be interesting for future studies to analyse the “costs” or lack of incentives in some contexts regarding international research activities. Academic reward systems in the European context are increasingly results-oriented, placing greater pressure on researchers in their international collaboration decisions to obtain higher scientific performance (Kwiek, 2020; Kyvik & Aksnes, 2015). However, in some cases, this pressure towards immediate scientific results may not always encourage international collaborative activities. This is the case for early career scholars, who may not be sufficiently incentivised to participate in these international activities, as they are focused on obtaining immediate scientific results to advance their careers and avoid career uncertainty (Skakni et al., 2019). It is clear that researchers will choose to collaborate internationally based on the compensation they receive compared to other ways of collaboration (Jeong et al., 2014). Similarly, there are other relevant barriers that should also be further analysed. For example, many researchers also find it discouraging to spend time on administrative activities once these collaborative activities are established and post-grant activities are developed. The individual decision to collaborate internationally must be analysed from a trade-off perspective between investment of resources and results obtained. Lack of support for such tasks can lead to administrative problems and coordination costs that create serious barriers to international collaboration (Fox et al., 2017).