Bibliometric analysis of studies on family firms

Abstract Several authors have highlighted the importance of family firms in the worldwide generation of wealth, wellbeing, and employment. Recently, the importance of family firms has resulted in the proliferation of many academic works in prestigious journals. Hence, studying their development and evolution is deemed necessary. This study conducts a bibliometric analysis of the literature on family firms to show the research trends and guide researchers in their work; it is conducted using a detailed and systematic study of the scientific production of papers on family firms published in the Web of Science (WoS) between 1975 and May 2020. Its contributions are as follows. First, it consolidates family firms as an area of research, which reflects on several papers focusing on this topic (1990 papers published in the WoS database, 55982 total citations). Second, it finds that family firm research has mainly developed in the last few years. Third, it discovers that Kellermanns and Chrisman are the most relevant authors in this field. Fourth, it suggests that the most influential journal is Family Business Review. Fifth, it finds that that the Mississippi State University is the most renowned family firm research institution. Sixth, it discovers that the United States has the highest production in the field. Finally, the bibliometric map identifies four clusters, the most relevant being the family firm theory and its evolution.


Introduction
Family businesses are the most widespread form of business organisations worldwide (Gedajlovic et al., 2012;G omez-Mej ıa et al., 2007;Hern andez-Perlines et al., 2019;Masulis et al., 2011;Poza & Daugherty 2013). This suggests that, in recent years, the growing research on business administration is focusing on family firms (Araya-Castillo et al., 2021;Chrisman et al., 2010;. Many researchers have taken an interest in analysing how these organisations work, especially in the field of business management (Benavides Velasco et al., 2011;Chrisman et al., 2008;Rodr ıguez Zapatero (2004) admit that the importance of family firms as a field of study is not consistent with its relevance in the economies of many countries. Admittedly, in recent years, work focusing on the multidisciplinary perspective of family firms had proliferated. These new developments recognise that family firms are the most widespread form of organisation worldwide (Miller et al., 2008).
According to Hern andez-Perlines et al. (2021), great diversity exists in the definition of family firms (Chua et al., 2012;Corbetta & Salvato, 2004). A review of the literature reveals three groups of definitions. The first are based on family involvement in both the ownership and management of the family business (Chua et al., 1999;Litz, 1995;Tatoglu et al., 2008). The second focus on the 'essence' of the family firm (Chrisman et al., 2005;Habbershon et al., 2003). Finally, the third centre on the dimensions through which families influence firms (Astrachan et al., 2002;Holt et al., 2010;Kellermanns et al., 2012).
Thus, 'family firm' has numerous definitions. It is, therefore, difficult to reach a consensus on the best, generally accepted definition (Hern andez-Perlines et al., 2020). Nevertheless, there are two common features in most family firm definitions (Franco & Prata, 2019). The first is ownership of capital since, in family firms, most shares belong to one or more family members (Kellermanns et al., 2008). While, the second is management since, in family firms, several members of the family participate in the management of the business (Kallmuenzer et al., 2018). Analysing family firms is challenging because of the existence of a wide variety of family firms (Cennamo et al., 2012;Chrisman & Patel, 2012;Llanos-Contreras & Alonso-Dos-Santos, 2018) due to varying levels of family involvement in the business (Samara & Berbegal-Mirabent, 2018).
Considering the above, it is evident that family firms have an important role in the global economy as they lead many sectors (Credit Suisse, 2018;Mallon et al., 2018;Hern andez-Perlines et al., 2020;PwC Global Family Business Survey, 2018). They are also the most widespread form of business organisations in any economy in the world (La Porta et al., 1999), and they are the most common type of business in the world, as reported by many authors (Gedajlovic et al., 2012;G omez-Mej ıa et al., 2007;Hern andez-Perlines et al., 2021;Masulis et al., 2011;Poza & Daugherty, 2013).
In this context, one can argue that the growth and functioning of many economies depends on the activity of family firms (Astrachan & Shanker, 2003;Memili et al., 2015). This is because, in many countries and regions, these firms represent an important part of the productive system (Hern andez-Perlines & Xu, 2018), as they are capable of generating stable employment (Fan et al., 2011;Hern andez-Perlines, 2018;Matthews et al., 2012).
There are also other studies that review the literature on family firms. Among them, Casillas and Acedo's (2007) study is worth highlighting. It uses the co-citations analysis of papers that appeared in Family Business Review between the years 1998 and 2005. This presents a longitudinal analysis that establishes patterns in the evolution of family firms as a scientific discipline.
Benavides Velasco et al. (2011) reviewed the literature on family firms using a bibliometric approach applied to papers appearing between the years 1961 and 2008 in journals of the Social Science Citation Index.
Also, Wright and Kellermanns' (2011) theoretical review of family firm literature enabled the systematic organisation of knowledge around this topic, developing a theoretical framework for future research. These authors identified a number of issues to be focused on in family firm research. Gedajlovic et al. (2012) theoretically studied the development of research in the field of family firms during that time and focused their analysis of family firms on the business management filed. They concluded that the firms differ in terms of their performance because of the institutional conditions that affect them.
Using the institutional approach, Bernadich and Urbano (2013) reviewed the literature on family firms based on the environmental factors influencing the creation and development of family firms. It is a bibliographic study of papers published in greatly relevant journals (indexed in the Journal Citation Reports (JCR)), books, and book chapters. The years between 1980 and 2011 were analysed.
Recently, Rovelli et al. (2021) have published a bibliometric study of 1381 papers appearing in the three main academic journals devoted exclusively to these businesses (Family Business Review, Journal of Family Business Strategy and Journal of Family Business Management). This study provides a comprehensive overview of the research on family firm and lays the groundwork for future developments.
This study conducts a bibliometric analysis of family firm research articles published in WoS-indexed journals between the period 1975 and May 2020. This study contributes to the literature because it is based on the WoS Core Collection, with which 1990 scientific papers on the subject were identified, with a total of 55,982 citations. Given this, the present investigation includes a greater number of articles in the review, and it is also more up-to-date (as of May 2020).

Methodology
This research reviews the different studies found in the literature on family firms and shows research trends with the main lines of action. With this in mind, bibliometric techniques are used (Toro-Jaramillo, 2017). That is, mathematical and statistical methods are applied to books and other written media (Groos & Pritchard, 1969), and thereby, are typically used to summarise, classify, and provide representative results of a set of bibliographic documents (Rovelli et al., 2021).
This methodology is an emerging and cutting-edge field of research in library and information science, which has developed extensively in recent decades (e.g., Astr€ om, 2007;Miguel & Dimitri, 2013;Vicencio-R ıos et al., 2020). This is relevant because, although bibliometrics is criticised for its inaccuracies and quantitative measurement limitations, it is very useful for a systematic literature review and the development of the state of the art (Toro-Jaramillo, 2017). This is because bibliometric resources allow the evaluation and analysis of academic production in different areas of science and knowledge (Mart ınez et al., 2015;Montero-D ıaz et al., 2018).
Therefore, the growth of scientific production in recent decades and its indexing in automated bibliographic databases have boosted the use of bibliometrics and the generation of indicators used to measure the results of scientific and technological activities (Sanz-Valero & Wanden-Berghe, 2017). The bibliometric analysis provides a detailed and systematised source of information on scientific production in a specific discipline (Merig o et al., 2015). This can be used as reference by researchers (Morales et al., 2017), and makes it possible to assess scientific activity, the impact of publications, and the available sources to guide new research (Moreno & Rosselli, 2012).
This study uses the bibliometric analysis as a methodology for analysing the literature on family firms. This type of analysis applies mathematical and statistical techniques to study the patterns of the publications and the use of different documents (Diodato & Gellaty, 2013).
This bibliometric analysis has been systematised in such a way that it follows the phases proposed by Velt et al. (2020).
The first phase, called formulation, describes the objectives of the study and poses the research questions that this study seeks to answer. This study analyses the literature specialising in family firms, and is a conclusive descriptive study (Malhotra, 2004).
The second stage, called identification, establishes search patterns (Wang & Chugh, 2014) based on the identification keywords and the time span of the search. Conducting bibliometric studies to classify the research on a topic requires a careful selection of database records (Hasper-Tabares et al., 2017). Following Vega-Muñoz et al. (2020), 'Family Firms' was established in Web of Science (WoS) as the keyword for the search vector. This database was considered because it is one of the most influential sources for searching scientific information, it has high search accessibility, and it provides knowledge about authors, articles, and journals dealing with the development of this subject matter (Granda-Orive et al., 2013). In addition, the WoS includes different indexes such as the Social Science Citation Index (SCI-E), the Social Science (SCI-E), Social Science Citation Index, and Emerging Sources Citation Index (Vega-Muñoz et al., 2020). When using the WoS-indexed research, the focus was on the most important research, and only peer-reviewed papers were considered (for instance, Keupp et al., 2012;Dada, 2018;Kauppi et al., 2018;Velt et al., 2020). The use of the keyword 'family firm' did not consider the different definitions of the term, as there is a great deal of controversy in specialised literature about its meaning (Hern andez-Perlines et al., 2021). The time span of analysis was from 1975 to May 2020 in the WoS.
The third stage coincided with the selection. Sound bibliometric analysis requires a careful selection of records from a given database (Hasper-Tabares et al., 2017). In this case, the information available in the WoS was considered due to its relevance (Granda-Orive et al., 2013). The search was carried out in the WoS Core Collection using the term 'family firms'. With this criterion, 1990 scientific papers on the subject were identified, with a total of 55,982 citations. Neither books nor proceedings were taken into consideration.
The fourth step verified the dataset. This process was carried out by authors dealing with a specific line of research in family firms and the ones known for publishing in high impact journals in the JCR.
The fifth stage focuses on the analysis of the data using the appropriate tools according to the proposed objectives and research questions. The bibliometric indicators used for the analysis were: articles, citations, journals, institutions, authors, and countries. An analysis of the bibliometric map in family firms was also carried out. It was, therefore, possible to draw a detailed map of key concepts based on frequency data and their respective clusters. A map of collaboration between authors was also included, as this helps identify the main actors in a scientific collaboration network and to see how the different actors are grouped in different areas within a network. The Impact Factors 2018 of each scientific journal was also analysed according to the JCR, as it is one of the most widely used indicators in the field of bibliometrics (Bosch et al., 2001), and the H-index for measuring the professional quality of publications in terms of the citations received by the scientific papers (G alvez Toro et al., 2006).
The bibliometric analysis conducted in this study was performed with the VOSviewer software, version 1.6.15 (Van Eck & Waltman, 2010) and Excel tools (Araya-Castillo et al., 2021).

Analysis of the results
The following pages show the studies conducted on the subject of family firms, and the undeveloped-or the ones with relatively minor scientific productions-lines of research. This situation is relevant because scientific production can only advance by building on previous work, with current work being the basis for future research and publications (for instance, Jim enez-Bucarey et al., 2020; Vicencio-R ıos et al., 2020; Araya-Castillo et al., 2021).

Papers and citations
Since the contribution of Jentoft's (1979) first paper to the literature on family firms, scientific production has been increasing. In 2020, there was a decrease in the number of publications, however, this is because the search was conducted in May (see Figure 1). Therefore, considering the historical evolution in the number of publications, scientific production in the family firm area is expected to exceed 2019 figures in 2020.
In relation to the above, the number of citations reported in the literature is also increasing. Indeed, the first reported citation dates back to the year 1985 and, since then, the number has increased significantly. The 2020 decrease is caused by the collection of databases in May (see Figure 2). Considering this, and the number of publications, the 2020 figures are expected to exceed those reached during 2019 accounting the historical evolution of the number of citations.
There are 55,982 citations in this topic. Table 1 shows that a low concentration of papers has a high number of citations, that is, only 11 papers (0.55% of the studies performed) out of a total of 1900 have over 500 citations. As for the rest, 18 papers have between 250 and 500 citations (0.90% of the studies conducted), 99 papers have between 100 and 250 citations (4.97% of the studies conducted), 143 papers have between 50 and 100 citations (7.19% of the studies conducted), and 1719 papers have fewer than 50 citations (86.38% of the studies conducted). A small part of the articles receiving more than 50 citations can be owed to the prolonged isolation of this field due to disconnection from the management areas.
In Table 2, considering the number of citations and the average number of citations per year, Anderson and Reeb's (2003) paper, published in the Journal of Finance, has the highest relevance in literature. It can also be observed that only two other papers exceed 1000 citations: Villalonga and Amit (2006) and G omez-Mej ıa et al. (2007), published in the Journal of Financial Economics and Administrative Science Quarterly, respectively. It is, therefore, evident that the greatest impact of the literature on family firms has occurred recently, specifically in the last 20 years.  Table 3 shows the 10 most influential authors, listed according to their contribution to this discipline. To measure the impact of the publications, the order of the authors was based on the number of papers and citations on this topic. In addition, the following were analysed: the number of papers and citations of the authors, their Hindex, the percentage of papers devoted to the study of family firms, and whether their publications are in the top 30.

Authors
Kellermanns has the largest number of published papers on family firms, with 2 of his papers in the top 30 most influential papers in the literature. Chrisman has the highest number of citations in literature on family firm, with 5 papers among the 30 most influential. He also has the highest H-index, papers, and citations (overall). Chua also stands out for having 4 papers among the 30 most influential articles in the literature on family firms, and Voordeckers for devoting the highest percentage of his papers (67%) to the subject under study.
In addition, the map of author collaboration in Figure 3 shows 9 scientific collaboration networks. Of these networks, 6 include the 10 most productive authors in family business research. Only the pink, brown, and orange networks do not include the most relevant authors in this field of literature.

Journals
Research on family firms has been published in many scientific journals. A selection was made of the 20 most influential journals dealing with this topic (ranked according to the total number of published papers on family firms). As shown in Table 4, the five most influential journals are: (1)  Moreover, the 5 most influential journals stand out from the 20 under consideration in terms of length and depth of the publications. In the 20 journals, the average number of published papers is 1980.45 while the average number of citations is 35,697.6. As for the 5 most relevant journals, the average number of published papers and citations is 1666 and 56,557, respectively.
Their impact factor was considered to measure their quality. This information was extracted from the WoS platform in the JCR. In 2018, for the 20 journals the average impact factor is 3.3777. However, the impact factor of the 5 journals with the highest relevance in the literature is 4.91.
Finally, if the H-index is calculated considering only family firms, differences can also be observed between the 20 most influential journals and the sample of the top 5. Thus, the average H-index value for the set of 20 journals is 16.75, while for the group of 5 top-ranked journals this value rises to 30.2.

Institutions
Merriam-Webster (2008) points out that higher education institutions provide facilities for teaching and research activities ( OBrien et al., 2010), where the nature of academic research is understood as the creation of knowledge (Adams et al., 2008). Based on this, Table 5 lists the 10 most influential institutions in family firm research.
In terms of the literature on family firms, the Mississippi State University has the highest H-index (35), papers published (80), and highest number of citations on this topic (5973). The J€ onk€ oping International Business School has the highest proportion of its scientific production devoted to family firm literature (32.84%), and the University of North Carolina is the one with the highest number of publications in the last 5 years (37,719).

Countries
To develop as a country, the creation of knowledge as a central element to improve the quality of life and progress (Sebasti an, 2007) is fundamental because, in the field of scientific dissemination and communication, the objective is to construct a map of accessible knowledge through citation indicators (Fern andez & Mart ın, 2018). In this context, research on family firms is analysed according to their geographical distribution. The results, sorted by country, are shown in Table 6 and Figure 4. However, there are peculiarities, such as the studies being written by researchers who are affiliated to institutions in different countries. This leads to an overestimation of the number of publications. The WoS platform counts the number of publications by also accounting for early access papers that are peer-reviewed, cited, and published. For this research, this implies that the absolute value of the number of published papers does not amount to 1990, and that the relative frequencies do not add up to 100%.
The United States is the leading country for family firm literature, with 29.6% of the scientific output. Next come Italy, Spain, and England, whose shares in the total  The case of Spain is unique, because it occupies third place in the ranking of countries with the highest number of publications in the family business field, only below the United States and Italy. However, no Spanish university is among the top 10 in the ranking, unlike American, Italian or British institutions, among others. This could be because Spanish institutions publish articles in collaboration with institutions in other countries that occupy leading positions in the family business literature, but they are not the ones leading these projects. As a result, they do not appear as affiliation of the first author.

Bibliometric map
An analysis of the bibliometric map of family firms was conducted. These are graphical summaries of documents obtained from a database of citations, words or phrases, or some bibliometric elements (Guzm an-S anchez & Trujillo-Cancino, 2013), which were performed with the VOSviewer software (Van Eck & Waltman, 2010), a tool used for the visualisation of bibliometric networks developed at the Centre for Science and Technology Studies (CWTS). Figure 5 shows that the network comprises five clusters in different colours in order of importance: red, green, blue, purple, and yellow. Each cluster contains the most commonly used concepts in family firm research and the size of each concept is related to the frequency of each item. Their network connections show the relationships of the concepts, so that related cognitive topics are located in close proximity, while the unrelated or barely related ones are distant.
In the red network, the key concepts are the following: family firms, theory, model, family, business, strategy, innovation, process, and others. These concepts refer to the literature that focuses on the theory of family firms and their evolution over time, the understanding of family businesses, and the implications of these studies for knowledge generation.
In the green network, the key concepts are the following: firm, evidence, family ownership, ownership, family control, control, shareholder, and others. These concepts refer to the literature that analyses the type of ownership and corporate governance in family firms.
In the blue network, the key concepts are the following: firm performance, board, director, and family involvement. These concepts refer to the literature that studies the participation of family members in family firms, and the impact this has on performance.
In the purple network, the key concepts are the following: CEO and founder. The concepts refer to the literature that analyses the foundation and leadership in family firms.  Finally, in the yellow network, the key concepts are the following: internationalisation and non-family firm. The concepts refer to the literature that analyses the differences that arise in the internationalisation process of family firms compared to nonfamily ones.

Conclusions
According to Hern andez-Perlines et al. (2020), in recent years, there has been a substantial increase in the number of publications studying family businesses to learn more about their behaviour (Chrisman et al., 2005;L opez-Fern andez et al., 2016;Nordqvist & Melin, 2010;Zahra et al., 2004). There are three reasons for this. First, family firms are the most common form of enterprise worldwide (Gedajlovic et al., 2012;G omez-Mej ıa et al., 2007;Hiebl et al., 2018;Masulis et al., 2011;Poza & Daugherty, 2013). Second, family firms are responsible for a large part of the economic growth and wellbeing of many countries (e.g., Astrachan & Shanker, 2003;Jaskiewicz et al., 2015;Pejic Bach et al., 2018). Third, the family firm is the form of enterprise that creates most employment (for example, Chang et al., 2009;Fan et al., 2011;Matthews et al., 2012).
Therefore, considering the importance and influence on family firm literature in recent years, this research uses a bibliometric methodology to study the development and evolution of academic literature in the business management field.
The study was based on 1990 papers (with a total of 55,982 citations) found in the WoS database and dated between 1975 and May 2020. The bibliometric indicators used for the analysis were: papers and citations, journals, institutions, authors and countries, which were used to analyse the bibliometric map in this line of research. The conclusion is that the first paper reported in the literature is the one written by Jentoft (1979), which was based on the succession of generations in small family firms. Since the publication of this paper, both the number of publications and citations have increased.
However, the literature on family firms has not yet heavily impacted and influenced business management as 86.38% of the publications reported have fewer than 50 citations. This is because family firm literature has become more relevant in recent years, with the three most relevant papers (in order of importance) being written by Anderson and Reeb (2003), Villalonga and Amit (2006), and G omez-Mej ıa et al. (2007).
Continuing with the analysis, Kellermanns and Chrisman are the most influential authors in the literature, both in terms of the number of published papers (Kellermanns) and the number of citations (Chrisman). The most important journal is Family Business Review, as it has the highest H-index and highest number of papers dealing with family firms only. For institutions, the Mississippi State University has the highest H-index, papers published, and citations on this topic. In terms of countries, the United States is the leading contributor to the literature on family firms, followed by Italy, Spain, and England (with their shares in the number of published papers exceeding 10%).
Finally, the bibliometric map shows five clusters, which are identified (in order of importance) by the colours red, green, blue, purple, and yellow. The red cluster focuses mainly on the development of the literature and its evolution over time; the green cluster on the ownership and control of family firms; the blue on family involvement in family firms and the impact this has on performance; the purple on the foundation and leadership in these types of firms; and the yellow on the international expansion of family firms.
Despite the thorough review, the descriptive quality could neither be improved by using other analytical tools or new statistical techniques nor could cover the papers published throughout the year 2020. Future research could enrich the study of the evolution of family firm literature by developing a scientometric study where, for example, studies connecting the family business field to the general management literature are analysed.
However, this research contributes to the literature as it provides information applicable to other researchers studying family firms.

Disclosure statement
No potential conflict of interest was reported by the authors.