Religious Tourism and Pilgrimage : Bibliometric Overview

This paper reviews the academic literature related to religious tourism through a bibliometric study and citations of articles indexed in the multidisciplinary database Web of Science (WoS). Through an advanced search by terms, a representative set of 103 documents that form the ad-hoc basis of the analysis were selected. In view of the results, it is concluded that the United States is at the forefront of research, with almost 20% of the articles affiliated to one of its centres, mainly university centres. Publications on religious tourism are currently in an exponential growth stage, supported by the annual increase in the number of citations received. These papers are published in a small number of journals well positioned in their JCR category, classified within the field of Social Sciences Research.


Introduction
Since ancient times, travelling for fervor and religious devotion purposes have been present in humanity.In this way, religious tourism starts from the moment people begin a journey due to a question of belief.It begins with a religious manifestation-the pilgrimage-where the pilgrim is considered a tourist of religious motivation (Digance 2003;Turner 1973;Turner and Turner 1978).
In a broad sense, religious tourism is any trip motivated, either exclusively or partly, by religious reasons (Rinschede 1992).However, religious issues are not the only ones considered by visitors to religious sites or events, and their motivation is composed of religious, cultural, traditional, spiritual, and landscape patterns, which often interact in the intention and decision to set out on a trip (Abbate and Nuovo 2013;Amaro et al. 2018;Drule et al. 2015;Hughes et al. 2013;Kaewumpai 2018;Kim and Kim 2018;Olsen 2013;Terzidou et al. 2018;Wang et al. 2016).This means that, in the last decades, traditional pilgrimage destinations have also become tourist sites of multifunctional nature (Kaufman 2005) that welcome moved by their religious beliefs and those interested in their historical heritage or architectural, cultural, or artistic value (Hughes et al. 2013;Hyde and Harman 2011;Fernandes et al. 2012;Geary 2018;Musa et al. 2017;Ramírez and Fernández 2018;Shinde 2007).It is generally acknowledged that tourist motivation is multi-faceted; that is, tourists have multiple motives for travelling, even within a single journey (Bowen and Clarke 2009;Pearce 1993;Ryan 2002;Uriely et al. 2002).Despite the worldwide trend toward secularization, in recent years, there has been a rediscovery of places and routes of a religious nature (Digance 2003).It is estimated that between 300 and 330 million people travel for religious reasons annually, generating an economic impact of about 18,000 million dollars (OMT 2014), representing a great opportunity for the development of many destinations.
As a growing phenomenon, and due to the dynamics it generates in the host communities, religious tourism has aroused interest among academics and businesspeople.For the former, the interest lies in the study of the motivations, interests, and spiritual or cultural needs which religious centres seem to have aroused (Abbate and Nuovo 2013;Amaro et al. 2018;Raj 2012; among others), while for the latter, it represents opportunities for additional income and increased employment (Egresi et al. 2014;Olsen 2012;Raj and Griffin 2015;Shackley 2001;Simone-Charteris and Boyd 2010;Tobón and Tobón 2013;Vukonic 2002).When considering its recent relevance, it is necessary to compile and analyse the academic papers published in the last years whose subject deals with this type of tourism.
Bibliographic reviews were considered the first step for conducting scientific studies, whose objective is to reach a good understanding of the state of the art by synthesizing existing knowledge in a reproducible way (Tranfield et al. 2003;Glover et al. 2014).Although there are limitations in its methodology, this type of review provides a reasonably detailed description of the body of the research carried out within the topic analyzed.
Driven by this circumstance, our main objective in this research is to present an in-depth analysis of the current state of research related to religious tourism through its bibliometric study-that is, through the use of mathematical and statistical methods to evaluate the existing scientific production to determine trends and identify areas of research in development or regression (Spinak 1996).
To develop the bibliometric analysis in any area of knowledge, the first step is to assess the databases available, their suitability, and the consequences of using one or another.The validity of the work will depend on the correct choice, since it must cover the field under study sufficiently (Bordons and Zulueta 1999).In order to achieve the proposed objectives, we have proceeded to review the documents published in indexed journals within the multidisciplinary database Web of Science (WoS) (Thomson Reuters), which provides an overview of international research production of any discipline of knowledge, both scientific and technological, humanistic and sociological, since 1945, becoming an ideal instrument for the approach to bibliometric studies.Through an advanced search of terms with a time limit in 2017, a set of 103 articles was selected that constitutes the empirical basis of the study.
This article is divided into four main sections.In the first section, and after this introduction, we proceed to review the academic literature in order to establish the theoretical framework of the research.Then, in Section 3, both the sources and the methodological process used to obtain the references that form the empirical basis of the study are described.In Section 4, the main results obtained in the study of the basic bibliometric indicators are detailed and discussed.In Section 5, the presentation of the main conclusions reached, and the limitations found during the investigation are discussed.
The following sections may be divided by subheadings.They should provide a concise and precise description of the experimental results, their interpretation, and the experimental conclusions that can be drawn.

Review of the Literature
Religiously motivated tourism is a worldwide phenomenon as old as religion itself and characteristic of all religious denominations (Lanczkowski 1982).Menhirs, burial mounds, and kromlecks (Stonehenge) had the same purpose as today's cathedrals, being religious centres that attracted believers from far and near (Roussel 1972).
The relationship between both terms, religion and tourism, has been studied from different perspectives (Collins-Kreiner 2010a, 2018;Terzidou et al. 2017).Bremer (2005) points out three approaches in which researchers place the intersections between religion and tourism: the spatial approach (pilgrims and tourists occupying the same space with different behaviors), the historical approach (relationship between religious forms of travel and tourism), and the cultural approach (pilgrimage and tourism as modern practices in a post-modern world).However, for Millán-Vázquez de la Torre et al. (2016), their link can be considered from two angles: on the one hand, as tourism motivated exclusively or partially by religious reasons (traditional view) (Rinschede 1992), and on the other hand, considering tourism as a contemporary spiritual journey (Sharpley 2009).
Religious tourism is linked to other types of tourism, especially holiday, cultural, social, and group tourism, which causes it to be linked to seasonality (Collins-Kreiner 2018;Lois-González and Santos 2015;Olsen and Timothy 2006;Oviedo et al. 2014;Raj and Morpeth 2007;Raj et al. 2015;Rinschede 1992;Timothy and Boyd 2006).Historically, religious trips were always multifunctional trips, even when religious factors seemed to predominate.However, in modern societies, religious motivation seems to be less important than in ancient societies (Rinschede 1992).
One of the most debated issues among the authors that address this type of tourism is the distinction between tourists and pilgrims, both actors in the religious tourism industry.The pilgrimage has often been defined as "a journey resulting from religious causes, externally to a holy site, and internally for spiritual purposes and internal understanding" (Barber 1993, p. 1), what it supposes the journey of a religious devotee to a sacred religious site (Turner 1973;Turner and Turner 1978).Others, such as Collins-Kreiner (2010b) and Morinis (1992), define pilgrimage as a journey to a site that embodies the highly valued, the deeply meaningful, or a source of core identity for the traveler.According Hyde and Harman (Hyde andHarman 2011, p. 1343), in an increasingly secular world, many non-religious people undertake journeys to sites of deep personal meaning.Thus, secular pilgrimages include journeys to the gravesites and memorials of celebrities, famous sporting grounds, or sites of political significance (Digance 2006;Kaelber 2006;Margry 2008a;Morinis 1992;Olsen and Timothy 2006).In short, Hyde and Harman (Hyde and Harman 2011) say that the pilgrimage is not just a religious phenomenon, and the old paradigm of pilgrimage, predicated on religious elements, no longer holds (Collins-Kreiner 2010a, 2010b).In its place must be recognized two alternative forms of pilgrimage: the religious and the secular.
In this context, it seems evident that the pilgrimage is a different form of tourism.To better understand the perceptions and expectations associated with tourism, Cohen (1979) argues that there is no "general type" of tourism and that different forms of tourism coexist with each other (Table 1).Thus, within the context of the pilgrimage, the experience of the pilgrim and his spiritual connection with a site would correspond to the existential form.On the contrary, visitors or tourists of religious sites can be classified in relation to the other four types of tourism.

Experiential
A quest for authenticity beyond the spatiality and temporality of everyday life Existential A journey to an external and elective spiritual site beyond the mainstream of a traveler's native experience Diversionary An escape from the ordinary Recreational Entertainment center travel that emphasizes the restorative capacity of travel-secular Experimental Travel intended to be out of the ordinary, unique and "alternative" Source: Cohen (1979).
While for some authors the pilgrim and the tourist have been considered separately as "religious travelers" or "holidaymakers", respectively (Smith 1992a;Cohen 1992), for others, they are linked to each other in a shared space.According a Hyde and Harman (Hyde andHarman 2011, p. 1345), "the pilgrim seeks to touch the sacred, that is, to visit the singular physical location they imagine embodies their deep religious values (Digance 2003;Eliade 1959;Eliade 1964;Morinis 1992;Smith 1992b).Many pilgrims seek an encounter with the divine (Ambrosio 2007;Digance 2003;Turner 1973;Turner and Turner 1978), or the pilgrimage is a culturally prescribed social obligation and/or, on occasion, a rite de passage (Ambrosio 2007;Cohen 1992;Morinis 1992;Smith 1992b;Turner and Turner 1978).The pilgrim may be motivated to gain religious merit or penitence for their sins (Cohen 1992;Digance 2003;Tomasi 2002;Turner 1973).Other pilgrims seek healing from illness or resolution of their worldly problems (Morinis 1992;Smith 1992b;Tomasi 2002;Turner 1973).At the other extreme, in an increasingly secular world where many individuals lack the grounding of a religious faith, according to Giddens (1991); Margry (2008b), andSchau andGilly (2003), existential uncertainties can drive a search for meaning, self-knowledge, and identity.Therefore, Hyde and Harman (Hyde andHarman 2011, p. 1345) affirm that non-religious people may attach sacred meaning to a wide variety of non-religious sites and seek a journey to such sites.Such journeys constitute secular pilgrimages (Collins-Kreiner 2010a;Margry 2008b;Olsen and Timothy 2006).
In spite of the differences in the perception and experiences of the tourist and the pilgrim, religious tourism emphasizes the interdependent nature of the two actors (tourist and pilgrim) and the social construction of a simultaneously sacred and secular site (Poria et al. 2004), differentiating themselves only in terms of their devotional bonds and preferences (Eade 1992).
Authors such as Smith (1992a) consider both groups within a continuous classification that goes from the pious pilgrimage based on faith to strictly secular tourism (Figure 1).In this classification, religious tourism would be in an intermediate position distinguishing, in turn, between a traveler who is more a pilgrim than a tourist, a traveler who is as much a pilgrim as a tourist or a traveler who is more a tourist than a pilgrim, depending on whether his faith or the profane predominate in his motivations and activities.This broad spectrum reflects the multiple and changing motivations of travelers, whose interests and activities can vary from pilgrimage to tourism and vice versa (Millán-Vázquez de la Torre et al. 2016).
Religions 2018, 9, x FOR PEER REVIEW 4 of 15 that non-religious people may attach sacred meaning to a wide variety of non-religious sites and seek a journey to such sites.Such journeys constitute secular pilgrimages (Collins-Kreiner 2010a; Margry 2008b; Olsen and Timothy 2006).
In spite of the differences in the perception and experiences of the tourist and the pilgrim, religious tourism emphasizes the interdependent nature of the two actors (tourist and pilgrim) and the social construction of a simultaneously sacred and secular site (Poria et al. 2004), differentiating themselves only in terms of their devotional bonds and preferences (Eade 1992).
Authors such as Smith (1992a) consider both groups within a continuous classification that goes from the pious pilgrimage based on faith to strictly secular tourism (Figure 1).In this classification, religious tourism would be in an intermediate position distinguishing, in turn, between a traveler who is more a pilgrim than a tourist, a traveler who is as much a pilgrim as a tourist or a traveler who is more a tourist than a pilgrim, depending on whether his faith or the profane predominate in his motivations and activities.This broad spectrum reflects the multiple and changing motivations of travelers, whose interests and activities can vary from pilgrimage to tourism and vice versa (Millán-Vázquez de la Torre et al. 2016).However, today, and due to the evolution that both terms have been experiencing, the limits between pilgrimage and tourism are vague.First, this is because the context has also changed.The pilgrimage, as it is currently conceived, hardly resembles the pilgrimages of the Middle Ages (Olsen 2010).Second, the term pilgrimage is increasingly used in broader and more secular contexts (Margry 2008b) by visitors and academics to refer to visits to tombs of war or celebrities, residences of celebrities, and funeral sites, which show characteristics traditionally associated with pilgrimages.Ground Zero in New York or Graceland are some examples.Third, the term tourism is increasingly considered to describe a spiritual journey (Willson et al. 2013).
Those studies that explore the experiences and the benefits related with religious tourism focus mainly on spiritual experiences, neglecting others such as social, educational, or restorative experiences (Bond et al. 2014).This is so, in spite of recognizing that managers of religious sites should offer visitors a wide range of activities, both spiritual and non-spiritual, that complement each other with the aim of providing a holistic experience (Tirca and Stanciulescu 2011;Weidenfeld and Ron 2008).Although the studies that address the other three types of experiences are scarcer if they have been addressed, for example, in relation to educational experiences, as in the studies of Nyaupane et al. (2015), Ramírez andFernández (2018), andSarris (2004).
Religious tourism generates benefits for all its stakeholders.On the one hand, religious entities can obtain a greater volume of donations and charity.On the other hand, the tourist motivated by faith participates in the resident trade by buying some souvenir or leaving some votive offering, which helps the reactivation of certain local craft activities (Fernández 2010).The religious tourist, in addition, is more faithful to the destinations than the traditional tourist with motivations different to faith, returning to the site in a shorter period of time (Robles 2001).In addition, the increase in tourists increases the income and benefits obtained by the companies dedicated to hospitality services in the area.However, today, and due to the evolution that both terms have been experiencing, the limits between pilgrimage and tourism are vague.First, this is because the context has also changed.The pilgrimage, as it is currently conceived, hardly resembles the pilgrimages of the Middle Ages (Olsen 2010).Second, the term pilgrimage is increasingly used in broader and more secular contexts (Margry 2008b) by visitors and academics to refer to visits to tombs of war or celebrities, residences of celebrities, and funeral sites, which show characteristics traditionally associated with pilgrimages.Ground Zero in New York or Graceland are some examples.Third, the term tourism is increasingly considered to describe a spiritual journey (Willson et al. 2013).
Those studies that explore the experiences and the benefits related with religious tourism focus mainly on spiritual experiences, neglecting others such as social, educational, or restorative experiences (Bond et al. 2014).This is so, in spite of recognizing that managers of religious sites should offer visitors a wide range of activities, both spiritual and non-spiritual, that complement each other with the aim of providing a holistic experience (Tirca and Stanciulescu 2011;Weidenfeld and Ron 2008).Although the studies that address the other three types of experiences are scarcer if they have been addressed, for example, in relation to educational experiences, as in the studies of Nyaupane et al. (2015); Ramírez andFernández (2018), andSarris (2004).
Religious tourism generates benefits for all its stakeholders.On the one hand, religious entities can obtain a greater volume of donations and charity.On the other hand, the tourist motivated by faith participates in the resident trade by buying some souvenir or leaving some votive offering, which helps the reactivation of certain local craft activities (Fernández 2010).The religious tourist, in addition, is more faithful to the destinations than the traditional tourist with motivations different to faith, returning to the site in a shorter period of time (Robles 2001).In addition, the increase in tourists increases the income and benefits obtained by the companies dedicated to hospitality services in the area.
In summary, as Rinschede 1992) states, the religious space is a multifunctional site in which, depending on the uses and the motivations that are derived in them, different forms of tourism can be found.That is, religious destinations are like any other tourist destination, products with numerous attributes that can satisfy the needs of both religious believers and other holidaymakers (Bond et al. 2014).

Methodology
This section includes the procedure followed for the preparation of the bibliometric study of the scientific production on religious tourism present in the WoS database.
Bibliometric analysis consists of the application of statistical methods with the objective of evaluating the advances and improvements of the knowledge related to a specific topic as well as the scientific quality and the influence of different publications and sources (Bouyssou and Marchant 2011).In this way, useful information is provided for those academics and professionals who try to analyse and study more deeply this particular field of research, since the bibliometric analysis determines a series of significant indicators to measure the bibliographic material such as the number of publications, the most prolific authors, the countries where this field of research is more popular, or the journals that pay more attention to its publication.Another good indicator that is used to measure the influence of a researcher is the number of citations and the citations/articles relationship or h index (Hirsch 2005) that provides the measure of the impact of a publication in relation to its number of citations.
The first step of the bibliometric analysis involves identifying the most useful databases for our study (Albort-Morant and Ribeiro-Soriano 2015).This work is based on the use of the Thomson Reuters Web of Science (WoS) database, considered one of the main documentary databases by researchers, providing research work in all disciplines with the highest quality standards (Merigó et al. 2015).
In order to be able to delimit the results to the area of religious tourism, we opted for a document tracking strategy by searching for terms whose equation is shown in Table 2.This form has the advantage of enabling to reach classified journals within all the thematic areas, therefore, considered more thorough (Corral and Canoves 2013).In addition, and following the outline of similar papers, in order to develop bibliometric indicators, only articles published in scientific journals are analysed because they constitute a representative sample of international scientific activity (Benavides-Velasco et al. 2011).Once the documents were selected, the ad hoc database required to analyse each of the basic variables of the bibliometric indicators was developed.One of the main problems that we can find when carrying out the analysis of the documents indexed in the different databases is a lack of standardization of the records, which is why it is essential to carry out a standardization process.For the specific case of authors´names, the main criterion used for their homogenization was the coincidence in the ascription of the institutional signature associated with the different variants of the names and surnames (Pérez et al. 1999).
Another fact that we must consider is that the compilation of documents in WoS was done in December 2017.Therefore, the results give an idea of the current situation and may change over time due to the emergence of new research on religious tourism.

Results and Discussion
A publication on religious tourism in WoS appeared for the first time in 1968.From that moment, and as shown in Figure 2, there has been a constant increase in the annual volume of studies, reaching the most significant figure in 2016 with 21 papers.As in other fields, the increase in publications in the last decade can be explained by two factors: first, the number of researchers around the world has increased exponentially, also increasing the number of submissions to journals, and second, the development of computers and the Internet that facilitates access to more updated information sources of each field (Merigó et al. 2015).
Religions 2018, 9, x FOR PEER REVIEW 6 of 15 Another fact that we must consider is that the compilation of documents in WoS was done in December 2017.Therefore, the results give an idea of the current situation and may change over time due to the emergence of new research on religious tourism.

Results and Discussion
A publication on religious tourism in WoS appeared for the first time in 1968.From that moment, and as shown in Figure 2, there has been a constant increase in the annual volume of studies, reaching the most significant figure in 2016 with 21 papers.As in other fields, the increase in publications in the last decade can be explained by two factors: first, the number of researchers around the world has increased exponentially, also increasing the number of submissions to journals, and second, the development of computers and the Internet that facilitates access to more updated information sources of each field (Merigó et al. 2015).The Law of Price ensures that the growth of scientific information is exponential.However, each discipline undergoes its own evolution through various stages: precursors (first publications), exponential growth (becomes research focus), and linear growth (growth slows down, review and archive of knowledge) (Price 1956).Based on what is observed in Figure 2, studies on religious tourism are in the exponential growth stage, adjusting the cumulative production function to an exponential equation with R 2 = 0.8649.
With regard to the number of citations that the articles indexed in WoS have received, in Figure 3, an increase over time is observed, exceeding the threshold of 200 in 2016.2.9% (3) of the articles get more than 50 citations, 10.7% (11) between 25-50 citations, 11.7% (12) between 10-25 citations, and 39.8% (41) between 1-10 citations.Only 36 of them, 35%, do not receive any citations.In the citation analysis, it should be taken into account that articles published over the last 10 years still do not show their maximum citation level and that access to the first studies is not always available to all, so they have a limited number of readers (Merigó et al. 2015).The Law of Price ensures that the growth of scientific information is exponential.However, each discipline undergoes its own evolution through various stages: precursors (first publications), exponential growth (becomes research focus), and linear growth (growth slows down, review and archive of knowledge) (Price 1956).Based on what is observed in Figure 2, studies on religious tourism are in the exponential growth stage, adjusting the cumulative production function to an exponential equation with R 2 = 0.8649.
With regard to the number of citations that the articles indexed in WoS have received, in Figure 3, an increase over time is observed, exceeding the threshold of 200 in 2016.2.9% (3) of the articles get more than 50 citations, 10.7% (11) between 25-50 citations, 11.7% (12) between 10-25 citations, and 39.8% (41) between 1-10 citations.Only 36 of them, 35%, do not receive any citations.In the citation analysis, it should be taken into account that articles published over the last 10 years still do not show their maximum citation level and that access to the first studies is not always available to all, so they have a limited number of readers (Merigó et al. 2015).
Religions 2018, 9, x FOR PEER REVIEW 6 of 15 Another fact that we must consider is that the compilation of documents in WoS was done in December 2017.Therefore, the results give an idea of the current situation and may change over time due to the emergence of new research on religious tourism.

Results and Discussion
A publication on religious tourism in WoS appeared for the first time in 1968.From that moment, and as shown in Figure 2, there has been a constant increase in the annual volume of studies, reaching the most significant figure in 2016 with 21 papers.As in other fields, the increase in publications in the last decade can be explained by two factors: first, the number of researchers around the world has increased exponentially, also increasing the number of submissions to journals, and second, the development of computers and the Internet that facilitates access to more updated information sources of each field (Merigó et al. 2015).The Law of Price ensures that the growth of scientific information is exponential.However, each discipline undergoes its own evolution through various stages: precursors (first publications), exponential growth (becomes research focus), and linear growth (growth slows down, review and archive of knowledge) (Price 1956).Based on what is observed in Figure 2, studies on religious tourism are in the exponential growth stage, adjusting the cumulative production function to an exponential equation with R 2 = 0.8649.
With regard to the number of citations that the articles indexed in WoS have received, in Figure 3, an increase over time is observed, exceeding the threshold of 200 in 2016.2.9% (3) of the articles get more than 50 citations, 10.7% (11) between 25-50 citations, 11.7% (12) between 10-25 citations, and 39.8% (41) between 1-10 citations.Only 36 of them, 35%, do not receive any citations.In the citation analysis, it should be taken into account that articles published over the last 10 years still do not show their maximum citation level and that access to the first studies is not always available to all, so they have a limited number of readers (Merigó et al. 2015).Two articles with more than 90 citations stand out due to the total number of citations received (Table 3): "Forms of Religious Tourism" (Rinschede 1992) and "Religious sites as tourism attractions in Europe" (Nolan and Nolan 1992).Source: Own elaboration.
Author productivity (both primary and secondary) is calculated based on the number of articles published by each of them.Following the criteria proposed by Lotka (1926), they are classified into: small producers (authors with only one published article), medium producers (authors with between two and nine published articles) and large producers (authors with 10 or more published articles).
Within the tourism form of religious tourism, and based on articles located in WoS, there are no authors considered as large producers.Collins-Kreiner, N. appears as the top author in the productivity ranking (Table 4) with six authorships.Only four other authors have written more than one article: Shinde, K, A. with three and Aukland, K., Cusack, CM, and Ryan, C. with two.In this way, and following Lotka, 2.73% of the authors are medium producers (5), while the remaining 97.27% (178) are considered small producers by having only one published article.This fact causes the average productivity per author (number of works published per author) to be 1.05.
By the number of citations received, and as shown in Table 4, we find Collins-Kreimer, N. again in the top position of the ranking with a total of 71 citations in six published articles.In addition, we must mention Ryan, C.; despite his low productivity, the average number of citations of his two articles is the highest (18.5).Another bibliometric indicator related to the authors is the Collaboration Index, considered one of the professionalization signs of the research field, since publications by numerous authors have a higher number of citations and impact than those by a single author (Granda-Orive et al. 2009).Table 5 shows how in the religious tourism field the total number of articles with multiple authorship is close to the sum of articles by a single author, 50 and 53 respectively, being those articles written by two authors, the ones with a higher average number of citations (13.48).Together with authorship, affiliation is one of the determining factors for the correct identification and recovery of the intellectual production of a researcher in the different databases (Table 6).In this regard, by countries and within the scientific production of publications related to religious tourism, one country stands out from the rest, the United States, with 19.42% (20) of the articles affiliated to one of its centres, mainly academic, and an average number of citations per article above 20.According to the Law of Bradford (1934), a small number of journals group most of the articles published related to an area, a fact that helps us identify the journals most used by researchers when it comes to disseminating their work (Figure 4).The Minimum Bradford Zone or Bradford Core (MBZ) is defined as the number of articles equal to half of the amount that appears in the last range of the list of journals sorted by production (those that produce a single article) (48) (Spinak 1996).
where MBZ: Minimun Bradford Zone.NR1a: Total of journals with a single article published.
Once the value of MBZ was calculated, and from the ranking of journals sorted in descending order of productivity, the MBZ is made up of those journals whose sum of articles was equal to the value of MBZ (24).In our bibliometric analysis, the MBZ is constituted by four journals-Annals of Tourism Research (11), International Journal of Tourism Research (7), Tourism Management (4), and Current Issues in Tourism (4).
(MBZ) is defined as the number of articles equal to half of the amount that appears in the last range of the list of journals sorted by production (those that produce a single article) (48) (Spinak 1996).
where MBZ: Minimun Bradford Zone.NR1a: Total of journals with a single article published Once the value of MBZ was calculated, and from the ranking of journals sorted in descending order of productivity, the MBZ is made up of those journals whose sum of articles was equal to the value of MBZ (24).In our bibliometric analysis, the MBZ is constituted by four journals-Annals of Tourism Research (11), International Journal of Tourism Research (7), Tourism Management (4), and Current Issues in Tourism (4).On the other hand, and taking into account the number of citations that journals receive for the publication of articles on religious tourism (Table 7), Annals of Tourism Research stands out with an average of 43.09 citations per published work, followed by Tourism Management with 22.50.Both publications are within the first quartile in the subarea of Hospitality, Leisure, Sport, and Tourism.
Based on the thematic classification of documents made by the WoS database, depending on the areas to which the journals where they are published belong to (Table 8), there is a main field of research in which articles on religious tourism are included: Social Sciences (Other Topics) with 51 articles.However, and regarding the average number of citations received, the Sociology area stands out, since its 12 articles have an average of 41.67 citations.On the other hand, and taking into account the number of citations that journals receive for the publication of articles on religious tourism (Table 7), Annals of Tourism Research stands out with an average of 43.09 citations per published work, followed by Tourism Management with 22.50.Both publications are within the first quartile in the subarea of Hospitality, Leisure, Sport, and Tourism.
Based on the thematic classification of documents made by the WoS database, depending on the areas to which the journals where they are published belong to (Table 8), there is a main field of research in which articles on religious tourism are included: Social Sciences (Other Topics) with 51 articles.However, and regarding the average number of citations received, the Sociology area stands out, since its 12 articles have an average of 41.67 citations.The most commonly used terms as keywords are related to the field of religious tourism; Pilgrimage and Religious Tourism (Figure 5).Other terms to consider are: Heritage, Development or Attraction.The most commonly used terms as keywords are related to the field of religious tourism; Pilgrimage and Religious Tourism (Figure 5).Other terms to consider are: Heritage, Development or Attraction.

Conclusions
This study illustrates the usefulness of bibliometric reviews of academic literature, not only as an instrument capable of identifying and classifying a wide variety of documents within a specific area of study but also to analyse existing information in order to show trends based on synthesized data.Based on the analysis of the selection of documents indexed in the main database of WoS, we can deduce a number of ideas that can help future researchers in the field of religious tourism.
The first publication of an academic paper related to Religious Tourism occurred at the end of the 1960s.Since then, the publication of articles has experienced an exponential growth at international level, supported by the annual increase in the number of citations received, an area in which Forms of Religious Tourism (Rinschede 1992) stands out with more than 135 citations.
Within the form of religious tourism, and based on the articles located in WoS, there are no authors considered as large producers, and almost 98% of them are classified as small producers because they have only one published work, which leads to a productivity index of close to 1.One country stands at the forefront of research on religious tourism, the United States, since almost 20% of the articles belong to one of its centres, mainly universities.In relation to the authorship of scientific production (collaboration index), the total number of articles with multiple authorship is close to the sum of articles by a single author, as those by two authors are the articles that receive a higher average number of citations.

Conclusions
This study illustrates the usefulness of bibliometric reviews of academic literature, not only as an instrument capable of identifying and classifying a wide variety of documents within a specific area of study but also to analyse existing information in order to show trends based on synthesized data.Based on the analysis of the selection of documents indexed in the main database of WoS, we can deduce a number of ideas that can help future researchers in the field of religious tourism.
The first publication of an academic paper related to Religious Tourism occurred at the end of the 1960s.Since then, the publication of articles has experienced an exponential growth at international level, supported by the annual increase in the number of citations received, an area in which Forms of Religious Tourism (Rinschede 1992) stands out with more than 135 citations.
Within the form of religious tourism, and based on the articles located in WoS, there are no authors considered as large producers, and almost 98% of them are classified as small producers because they have only one published work, which leads to a productivity index of close to 1.One country stands at the forefront of research on religious tourism, the United States, since almost 20% of the articles belong to one of its centres, mainly universities.In relation to the authorship of scientific production (collaboration index), the total number of articles with multiple authorship is close to the sum of articles by a single author, as those by two authors are the articles that receive a higher average number of citations.
On the other hand, the core of the main journals that collect articles on religious tourism (Bradford core) is formed by only four publications, due to the number of articles and the number of citations received, Annals of Tourism Research, of the first quartile in the subarea of Hospitality, Leisure, Sport, and Tourism.Regarding the thematic classification of documents made by the WoS database, based on the areas that the journals where they are published belong to, there is a main field of research in which articles on religious tourism are included: Social Sciences (Other Topics).However, regarding the average number of citations received, the Sociology area stands out, since its articles have an average of more than 40 citations.
When interpreting the results in any bibliometric study, the limitation of choosing a specific database and a specific search equation must be taken into account.On the other hand, our aim has not been to evaluate the quality of the content of the selected articles, an objective that can be considered in a subsequent investigation, but a descriptive-quantitative analysis of the articles and citations related to religious tourism present in WoS.In order to expand the present study, it would be interesting to examine documents indexed in other databases, together with the possibility of including comparative studies between them.

Figure 2 .
Figure 2. Annual number and growth of articles on Religious Tourism indexed in WoS.(Source: Own elaboration).

Figure 3 .
Figure 3. Annual number and growth of citations received by articles on Religious Tourism.(Source: Own elaboration).

Figure 2 .
Figure 2. Annual number and growth of articles on Religious Tourism indexed in WoS.(Source: Own elaboration).

Figure 2 .
Figure 2. Annual number and growth of articles on Religious Tourism indexed in WoS.(Source: Own elaboration).

Figure 3 .
Figure 3. Annual number and growth of citations received by articles on Religious Tourism.(Source: Own elaboration).

Figure 3 .
Figure 3. Annual number and growth of citations received by articles on Religious Tourism.(Source: Own elaboration).

Figure 5 .
Figure 5. Cloud of keywords included in the articles.(Source: Own elaboration).

Figure 5 .
Figure 5. Cloud of keywords included in the articles.(Source: Own elaboration).

Table 2 .
Search Strategy in WoS.

Table 3 .
Most cited articles in WoS about Religious Tourism.
* f = frequency (number of articles published); hi% = relative frequency; Hi% = cumulative frequency; TC= total number of citations received for published articles; C/f = average of citations received for published articles.Source: Own elaboration.

Table 6 .
Countries of Affiliation of the articles on Religious Tourism according to the WoS database.
* f = frequency (number of articles published); hi% = relative frequency; Hi% = cumulative frequency; TC= total number of citations received for published articles; C/f = average of citations received for published articles; h-index = Hirsch's index.Source: Own elaboration.

Table 7 .
Ranking of the most productive magazines.

Table 7 .
Ranking of the most productive magazines.

Table 8 .
Main Thematic Areas where articles on Religious Tourism are collected.
* f = frequency (number of articles published); hi% = relative frequency; Hi% = cumulative frequency; TC= total number of citations received for published articles; C/f = average of citations received for published articles; h-index = Hirsch's index.Source: Own elaboration.

Table 8 .
Main Thematic Areas where articles on Religious Tourism are collected.
* f = frequency (number of articles published); hi% = relative frequency; Hi% = cumulative frequency; TC= total number of citations received for published articles; C/f = average of citations received for published articles; h-index = Hirsch's index.Source: Own elaboration.