How Does Religion A ﬀ ect Giving to Outgroups and Secular Organizations? A Systematic Literature Review

: Although religious giving represents the largest sector of charitable giving in the US, its overall impact on social welfare has been questioned, pointing to the possibility that the majority of funding might stay within the religious community, with little beneﬁt to outgroups or secular charity. Despite multiple studies showing a positive relationship between religion and secular and outgroup giving, some empirical ﬁndings show a negative or non-signiﬁcant relationship. By employing a systematic literature review, the current study explores theories and empirical evidence to provide an integrative framework that identiﬁes the mechanisms and directions through which religion a ﬀ ects giving to outgroups and secular organizations. The study also compares the major ﬁve religious traditions and giving to outgroups and secular organizations. The study ﬁnds that religious teachings, norms, values, social network, and private rituals, determine the direction of the relationship between religion and giving to outgroups and secular organizations. The study concludes that, despite the dominant positive relationship between religion and giving to outgroup and secular organizations, there remains heterogeneity among the studies based on their location, operationalization of religion and secular giving, and methodology used. The study also poses some implication questions and points out future research directions.


Introduction
When examining the role of religion in charitable giving to non-profit and philanthropic organizations, scholars have most often focused on defining the religious or secular nature of the recipient organization based on its stated activity. Categorizing by religious activity significantly limits the types of organizations labeled as religious: congregations, denominations, missionary societies, and religious media. Yet, even with this narrow definition, religious giving represents the largest subsector of charitable contributions (29%) in the United States (Lincoln et al. 2008). According to the Giving USA (2020) report, religious giving represented $128.17 billion, almost twice the amount given to the next highest non-profit sector, education. There are over 350,000 congregations alone in the United States. Even so, some scholars have questioned the overall impact of religious giving if the majority of funding stays within the religious community and benefits its affiliated members rather than the public welfare of broader society (Turner 2005).
Many other organizations may claim a religious identity even if their stated purpose is not a religious activity. For example, religiously affiliated hospitals, schools, or social service agencies may operate with staff, mission statements, or fundraising appeals defined by their religious identity, but scholars in non-profit, philanthropic, and organizational studies generally classify them as secular based on their main purpose or activity-such as healthcare, education, or human services. Some studies estimate that charitable giving to organizations with a religious identity, if not a religious activity, may represent another 32% of all U.S. charitable giving and a significant percentage of the non-profit organizations in many subsectors McKitrick et al. 2013). Yet, the scholarly literature continues to consider these organizations as secular in contrast to those with a strictly religious purpose. Other disciplines, such as religious studies, have a well-defined scholarship on the nature of the secular that may be much more robust than the simple classification of organizations based on explicit religious activity. While we support introducing a more nuanced analysis of the nature of religiosity and secularity in the study of charitable giving and organizations, our literature review follows the accepted definitions in this paper. We hope that our analysis of religion's role in giving both to secular organizations and individuals or organizations outside of one's own faith group, or outgroups (Morton et al. 2020;Cheung and Kuah 2019), may help to expand the study of religiosity outside the organizations committed to a narrow definition of religious activity, as well the interaction of religion and the secular when focused on general social welfare and the common good.
The existing studies identify two types of religious giving-the religious motivation behind charitable gifts and giving that explicitly goes to religious organizations (Vacek 2010;Vaidyanathan and Snell 2011)-whereas giving to outgroup and secular organizations is measured as giving to individuals outside of one's own faith group (Morton et al. 2020) and giving to non-congregation and non-religious organizations (Cheung and Kuah 2019). Nonetheless, these categorizations, as mentioned above, are problematic because, unlike congregations and denominations that are solely religious, there are organizations that do not have an explicitly religious purpose but maintain elements of religion in either their identity or activity. Introducing these organizations in the analysis of giving to secular organizations and outgroups may also expand the discussion of how faith expands general social welfare.
While maintaining the current definitions of religion and secular giving, even with their limitations, existing studies analyze religion's effect on the motivations of individuals' overall charitable giving in two ways-through religious affiliation, such as individuals' particular religion identification, and religious intensity, such as the typology of beliefs or practices and level of engagement or attendance at religious services (Berger 2006;Carabain and Bekkers 2012). Most studies, including literature reviews on the effect of religion on prosociality, agree that religious affiliation and engagement increase religious giving (a charitable giving category as defined above, such as within the U.S. Internal Revenue Service's National Taxonomy of Exempt Entities (NTEE) Codes).
Findings, however, are mixed when it comes to the influence of religion on secular giving. While some scholars provide theoretical and empirical evidence for the positive influence of religion on secular giving, others find the opposite effect or no effect at all Diop et al. 2018;Eckel and Grossman 2004;Hill and Vaidyanathan 2011;Ottoni-Wilhelm 2010;Wiepking et al. 2014;Wuthnow 1990). To date, an overview that maps the existing knowledge about these relationships is lacking amidst the vast reviews on the effect of religion on prosociality or giving in general Preston et al. 2010). The first aim of this review, therefore, is to systematically summarize scattered evidence and provide an interdisciplinary overview of empirical findings on the relationship between religion and giving exclusively to outgroups and secular organizations and develop an integrative and interdisciplinary framework to identify the underlying mechanisms explaining the effects of religion on secular giving.
Moreover, there is evidence that particular religious identities serve as better mechanisms through which religion affects secular giving. For example, Ottoni- Wilhelm (2010) finds that being Jewish is associated with a higher probability and magnitude of giving to secular organizations compared to other religions, even after controlling for income. However, we know little about how being a follower of one religion compares to others in encouraging secular giving. Thus, the second aim of this study is to offer a comparative analysis of how different religious traditions understand and practice secular giving.
The corresponding research questions are, therefore, the following: How does religion affect secular giving, and which mechanisms are at work here? Are particular religious traditions more effective in encouraging members to internalize generosity towards secular organizations? To answer these questions, we conduct a systematic literature review (SLR), deliver an extensive overview of existing empirical evidence, and provide a conceptual framework identifying the mechanisms for how religion affects secular giving. The study is based on a literature search using the ATLA religion database (a unique index of academic journal articles in religion) and the Web of Science Social Sciences Citation Index (SSCI) database (a multi-disciplinary index in the social-science field). Using relevant keywords, we found 2622 studies from our database search. We followed specific inclusion criteria such as the requirement that the studies primarily discuss or test the relationship between religion and any type of secular giving and focus on monetary giving at an individual level of analysis. After an initial abstract screening and an in-depth in-text screening, the study included 77 studies for this systematic literature review. We found that there were similarities and variations in how the Big Five religious traditions (Christianity, Islam, Judaism, Hinduism, and Buddhism) teach and practice giving to outgroups and secular organizations. We also found that religious norms and group affiliation; network in religious community and service attendance; and private rituals were the three dominant pathways that determine how religion affects giving to outgroup and secular organizations.
This study can contribute to the existing knowledge in two ways. First, this review will be the first that systematically maps research on the effect of religion on giving exclusively to outgroups and secular organizations and compare the teachings and practices of external giving among the Big Five religious traditions. Second, it will depict the current state of empirical evidence and theoretical explanations and provide an integrative framework by identifying the mechanisms through which religion affects giving to outgroups and secular organizations, which may benefit future research.

Method: Systematic Literature Review
We used a systematic literature review method, a replicable research design that enables the aggregation of theoretical explanation on a topic as well as empirical findings (Schröder and Neumayr 2019;Denyer and Tranfield 2009). We followed Schröder and Neumayr (2019) three broad methodological steps. First, we located, selected, and evaluated the studies to be included in our study. Second, we analyzed and synthesized the final studies that are included in our research using descriptive and interpretive analyses such as tables, a developing concept matrix, narration, and graphical representation. Third, we reported the results (Denyer and Tranfield 2009;Schröder and Neumayr 2019).
For the first step-locating the studies-we conducted a literature search using the ATLA religion database and the Web of Science Social Sciences Citation Index (SSCI) database. We limited our search to studies published on the topic in English before 15 April 2020. Based on the initial literature review, we came up with keywords that illustrated both religion and secular giving, the two constructs that we aim to relate. Table 1 below shows the keywords and their combinations and the total number of studies we found in the database search.
Of the total 2622 studies identified, based on abstract screening, we identified 240 studies that met the following three primary inclusion criteria (see Appendix B for more inclusion criteria): i.
Studies that primarily discuss or test the relationship between religion and any type of secular giving; ii.
Studies that focus only on a monetary donation; and iii.
Studies that are at the individual level of analysis.
We also included an additional ten studies meeting the inclusion criteria that served to identify keywords and concepts on the topic at the beginning of our study. After retrieving the 240 screened Religions 2020, 11, 405 4 of 22 studies from the database search and the ten additional studies, we reviewed the full text of a total of 250 studies for further screening and collected the metadata in Excel. We finally identified 77 studies that met all of our inclusion criteria. Out of these studies, 37 were theoretical, and 40 were empirical studies. See Figure 1 below for the systematic literature review process. Table 1. Keywords, combinations, and total number of studies identified.

Combination of Keywords for Search Strings
No. of Studies

Religion
Giving SSCI ATLA religion* OR religious OR religiosity* OR spirituality* OR faith* OR "faith-based" OR "belief traditions" OR "religious affiliation" OR "religious service attendance" OR "religious attendance" OR congregation OR denomination OR Christian* OR Christianity OR Islam* OR Muslim* OR Hindu* OR Hinduism OR Buddh* OR Buddhism OR Juda* OR Judaism AND donation OR "prosocial behavi*" OR prosocial OR generosity OR charity* OR philanthropy OR "provision of public good" OR "public good" OR "social welfare" OR "financial donation*" OR "nonprofit" OR nonprofit* OR nongovernment OR "nongovernmental organi*" 1861 820 AND Secular Giving 377 44 (giving OR gift* OR donation OR charity OR "financial donation" OR generosity OR prosocial* OR philanthropy) AND (secular OR "social service" OR "arts culture and humanities" OR "education sector" OR "environment and animals" OR "health sector" OR "human services" OR "international affair" OR "foreign affair" OR "public and social benefit" OR "mutual benefit" OR "membership benefit" OR NTEE OR "basic necessity organization*") Total number of studies from SSCI 2238 Total number of studies from ATLA 864

Number of studies after removing duplicates 2622
Religions 2020, 11, x 5 of 25 from the literature in an evolving framework of mechanisms to explore the theories and mechanisms at work. In the last step of the systematic review process, we again followed Schröder and Neumayr (2019), where results were first described by aggregating the empirical studies' results in a tabular overview. Then, we presented a conceptual framework on the theoretical explanations and mechanisms that lie in between religion and giving to outgroups and secular organizations. We describe each mechanism in detail in the next subsections.

A General Overview of the Studies Included and the Empirical Results
The 77 studies we have identified come from various disciplines, including economics, sociology, theology, political science, psychology, public policy, finance, comparative studies, and For the second step-analysis and synthesis-we developed an excel metadata that contained basic information such as author(s), the geographical focus of the studies, sample size, methodology, the theory used, and findings. These data were used to compare the studies and evaluate the overarching patterns in their theoretical explanations and findings. Then, we applied an inductive open coding approach that allowed coding and analysis to go together as concepts developed in an iterative process of reading and re-reading the included studies (Schröder and Neumayr 2019). We then followed a Framework Synthesis approach (Schröder and Neumayr 2019), constructing findings from the literature in an evolving framework of mechanisms to explore the theories and mechanisms at work.
In the last step of the systematic review process, we again followed Schröder and Neumayr (2019), where results were first described by aggregating the empirical studies' results in a tabular overview. Then, we presented a conceptual framework on the theoretical explanations and mechanisms that lie in between religion and giving to outgroups and secular organizations. We describe each mechanism in detail in the next subsections.

A General Overview of the Studies Included and the Empirical Results
The 77 studies we have identified come from various disciplines, including economics, sociology, theology, political science, psychology, public policy, finance, comparative studies, and social work. Most of the studies included appeared to have been published after 1990, despite the fact that we had no restriction on years of publication. Out of the 77 studies included, 38 of them refer to data about the US, 11 about Europe, 7 about Asia, 6 about Africa, 3 about Canada, 2 about Australia, and the rest are either cross-national or non-country-specific studies. Of the 77 studies included, 40 used empirical data to measure religiosity and its effect on giving to outgroup or secular organizations. Some of the 40 empirical studies include religion as a control variable in predicting giving to non-religious organizations. In Table A1 in Appendix A, we present the 40 empirical studies in alphabetical order, including their geographical focus, sample size, religious measure, type of secular giving, and the positive or negative relationship for the incidence and/or amount of giving to outgroups and secular organizations. In the table, we also include the moderating or important control variables that these studies used. Out of these 40 empirical studies, 29 employed survey data, 6 used experiments, 3 used a qualitative study design (in-depth interviews and observations), and the last 2 applied mixed-method design. We also organized Table A1 according to how the religion variable(s) was/were included in the studies-whether as the main predictor, one of the many independent or control variables, or results from qualitative and mixed-method designs.

Religion and Giving to Out-Outgroup and Secular Organizations Measures
The included studies vary in how they operationalize religion. Most of the studies used religious affiliation-how individuals identify themselves with regard to one of the Big Five religions-and religious service attendance-how frequently participants attend religious services (see (Carabain and Bekkers 2012;Eagle David and Read 2018;Hill and Vaidyanathan 2011;Lyons and Nivison-Smith 2006)). The other dominant measure refers to the levels of religious intensity. To measure this form of religiosity, the studies used scales such as the family environment scale (FES), the supernatural belief scale, and other self-reported Likert-scales that range from 1 (not religious) to 10 (very religious). Studies also incorporated various dimensions of religiosity such as practice, belief, and experience, as well as the consequence or importance of religion in the participants' lives (Dilmaghani 2018;Diop et al. 2018). A few studies also measured religiosity by asking if individuals followed specific religious practices such as keeping Shabbat or Kosher (Sansani and Rozental 2018). Experimental studies often used religious primes such as prayer, religious or God-related thinking, and religious locations (Greenway et al. 2018;Morton et al. 2020;Thunstrom 2020;Xygalatas et al. 2016). Specific religious or denominational identities were also used to compare giving practices across various faith traditions Religions 2020, 11, 405 6 of 22 Ottoni-Wilhelm 2010). Others also measured the role conversion may play in the intensity of religious identity or activity (Curtis et al. 2015). Some studies focused on moral foundations, testing whether religious people across faith traditions share values such as a moral responsibility to help others out of duty to their community or God (Shepherd et al. 2019). Other traditional measures, such as the role of parental and partner religiosity and giving to religious organizations, were also used in predicting giving to secular organizations (Wilhelm et al. 2008).
In measuring giving to outgroups, in particular, studies most often used measures such as giving to other individuals who are following a different religion than the giver. For instance, in one experiment, researchers tracked whether Muslim individuals donated when presented with non-Muslim students in need (Morton et al. 2020). Other studies tracked giving to Muslim charity organizations by professed Christians (Shepherd et al. 2019). Still, others measured the variation in giving behavior based on religious location. For example, would Christians give more when located at a church versus when present at a Hindu temple? (Xygalatas et al. 2016).
On the other hand, giving to secular organizations has been defined as giving to a variety of organizations without a specific religious purpose or activity. These "secular or external organizations" include those working on causes such as education, health, foreign/international aid, poverty, basic necessities, humanitarian aid, human rights, animal rights, cultural purposes, sports and museums, the elderly, and trade unions. As noted above, many of these organizations may have a religious identity, but they are most often classified as secular in the literature reviewed because their primary activity is classified with another specific purpose. Giving behavior for both outgroups and secular organizations is measured in both the actual amount of donations and the attitude or willingness to give.

Mechanisms Explaining How Religion Affects Giving to Outgroup and Secular Organizations
In our literature review of the empirical and theoretical studies, we identified three key mechanisms most often employed to explain the effect of religion on giving to outgroup and secular organizations. Two of these mechanisms predominated. The first we label as convictions: the beliefs, values, norms, and identities within a particular religion. The second we label as the socially integrated community most often tracked through social networks, religious engagement, and attendance (Wuthnow 1990). We have identified a third mechanism through our literature review that we have categorized as personal ritual-the private experience of connecting with an individual's belief through practices such as private prayer and meditation. This third mechanism has gained increasing attention in more recent studies (Thunstrom 2020;Greenway et al. 2018). Some scholars may integrate what we label as a distinct third mechanism into one of the previous two. For example, they may consider private religious practice complying with the teachings or norms of the given religion or they may observe such rituals occurring during communal religious services. However, articles in our systematic literature review focused on private religious ritual as a distinct mechanism for a particular purpose. For example, some scholars noted that prayer sometimes served as a "substitution" for charitable giving with the agency of praying for another, providing help over donating. In another set of studies, priming individuals through prayer or meditation indicated the possibility of an increased "empathy effect"-a concern for others that then entailed increased giving. The number of studies with an explicit focus on this mechanism and the ways in which they examined religion's role in predicting religious and secular giving as well as giving to both ingroup and outgroup has led us to categorize this pathway as a third independent mechanism.
As shown in Figure 2 below, out of the three mechanisms we identified, two of them dominantly point towards the channels at work for a positive relationship, while the third shows both a positive and negative relationship depending on which aspect of the mechanism is at work. The following figure depicts the mechanisms and the positive and negative relationships between the constructs that we are explaining. We also explain each of the mechanisms in the following separate subsections.
outgroup has led us to categorize this pathway as a third independent mechanism.
As shown in Figure 2 below, out of the three mechanisms we identified, two of them dominantly point towards the channels at work for a positive relationship, while the third shows both a positive and negative relationship depending on which aspect of the mechanism is at work. The following figure depicts the mechanisms and the positive and negative relationships between the constructs that we are explaining. We also explain each of the mechanisms in the following separate subsections.

Identity, Values, Norms, Teachings, and Affiliation
One of the most frequent explanations for the relationship between religion and giving to outgroup and secular organizations is religious identity, values, and norms developed within particular religious traditions. Sociologist Emile Durkheim's social integration theory remains a popular way of explaining how religious affiliation affects giving. The social integration theory states that religion provides norms such as collectivism, altruism, and principlism reinforced through collective ritual action (Regnerus et al. 1998;Reitsma et al. 2006). When focused more explicitly on religious teaching, other scholars have claimed that a shared core value of empathy is a key component influencing generous behaviors toward others (Ottoni-Wilhelm 2010).
When focusing on a particular religious tradition's distinct set of common values or religious teachings, some scholars argue that religion fosters only ingroup giving (Turner 2005). From our systematic literature review, however, most studies found that religiously affiliated individuals are also more likely to give to secular causes than those with no religious commitments. For example, Brooks (2004) found that religious people are ten times more likely to give to secular causes than those with no religion. A handful of studies, however, do note that religious affiliation has a negative effect when measuring giving to some secular charity organizations against giving to one's own religious ingroup Neumayr and Handy 2019;Showers et al. 2011).
The theoretical studies also demonstrated how giving to charitable causes remains a historical and contemporary phenomenon shared among all of the Big Five religions, while also noting distinct variations in how they conceptualize and practice giving or helping others. These studies illustrate the potential limitations of defining charitable giving as "religious" or "secular" based on a non-profit organization's narrow purpose. The teachings, values, and norms of most religious traditions themselves do not conceive of the "secular" in contrast to religion even if they may create boundaries between in-and outgroups. In Islam, for example, charitable giving (zakat) is one of the five major pillars of the faith and constitutes an essential faith practice and duty to God, requiring the faithful to give to those in need (Carabain and Bekkers 2012). At the same time, the faith may also discourage public displays of giving that might lead to some individuals downplaying their religious giving (Diop et al. 2018). Therefore, Muslims across many cultures have established formal and informal practices to nurture the institution of charity within their local communities as well as broader international communities (Jamal et al. 2019;Maarouf 2012). Of course, religious communities also extend beyond local communities, and Muslims, like other religious groups, debate whether it is best to support local needs both inside and outside their community or to support a global religious ingroup (umma). In an experimental study, Morton et al. (2020) found that Muslims give to outgroups more than to the ingroup, and the result would be the same if they were asked to give anonymously. However, evidence from survey data from the Netherlands showed that Muslims tend to give more to religious organizations compared to secular organizations (Carabain and Bekkers 2012). As they were predominantly first or second-generation immigrants to the Netherlands, in this study, questions of religious tradition merged with issues of migration, integration, and assimilation to make sense of trends and motivations in giving.
Similarly, Judaism requires those who practice the faith to help those who are in need within the community. Judaism promotes empathy by asking practitioners to put themselves in the position of one another . Moreover, through its Hebraic roots, philanthropy is mostly considered as a form of social justice (Berger and Gainer 2002). In fact, tzedakah (charitable giving) derives from tzedek (justice). It may also be related to chesed (mercy or loving kindness), which compels all Jews to give compassionately to those who are considered less fortunate and in need, both in and outside of their communities (Berger and Gainer 2002). In this regard, Ottoni-Wilhelm (2010) also argues that Jews, compared to Protestants and Catholics, are more likely to give to a secular organization after controlling for income, and when they do give, they give in larger amounts. Ottoni- Wilhelm (2010) argues that Judaism is successful in combining its own religious identity with empathy through its teaching (with the help of scriptural stories that relate Jews with historical poverty and slavery) to help others, so that the Jews' giving behavior extends to outgroups and secular organizations.
In Hinduism, the major non-reciprocal giving unmotivated by immediate self-interest is known as dana, a religious duty to give (Carabain and Bekkers 2012). The four types of dana-dakshina, bhiksha, bheeka, and annadan-entail giving to the temple, giving goods and food to religious monks, giving to the poor and needy, and sharing food with others, respectively (Carabain and Bekkers 2012). Empirically, Carabain and Bekkers (2012) found that Hindus tend to engage in more secular giving compared to religious giving. However, Carabain and Bekkers partially explain the result as dependent on the earlier migration history and greater integration of the Hindu community in the Netherlands, in contrast to more recent Muslim immigration.
In Buddhism, God is not a concrete entity; therefore, motivations to give to charity are driven by a relative point of view in which altruism is the practice of ridding oneself of desire (De Lubac 1988). Bodhicitta-the practice of giving and helping-is the state of mind resolved upon becoming a buddha and acquiring specific beliefs about the human potential, which may appear most contrary to charity (love), defined in other religious traditions as a gift from God and then shared with the broader humanity (Perera 2015).
Christianity promotes the teaching of the love of neighbors through love (agape) (Marion 1992;Perera 2015). An interview in a qualitative study in China states that "Donating to the poor is one of the basic teachings God gives to humans. Throughout the Bible, God wants those who are rich and abundant to help the poor. The former should never exploit the latter" (Cheung and Kuah 2019, p. 4). Christians are encouraged to practice giving as a virtue (Marion 1992). The Gospel of Luke within the Christian Scriptures contains important clues about how Christians should care for the poor and give to others to combat poverty both inside and outside their particular religious tradition (Jeyaraj 2004).
The theoretical studies that investigate the adage that "charity begins at home" acknowledge that in Christianity, as in other religious traditions, there is a belief and practice among some that giving must start from the ingroup and then extend to the outgroup. Cheung and Kuah (2019) claim that Christians believe that ingroup-giving is a duty that is commanded by God, while giving to outgroups is thought of as an additional (non-duty) but desirable action. On the other hand, the teaching to love one's neighbor demonstrates a stream within Christianity that encourages giving to outgroups (Rufft 2007). In the biblical parable of the Good Samaritan, Jesus encourages his listeners to redefine who qualifies as a neighbor as those in need, whether they belong to the in-or outgroup. Within a particular religious tradition such as Christianity, studies also show variations concerning giving to secular organizations. Among different denominations, some studies find that Protestants give more to secular organizations, while others find that Catholics give more (van Elk et al. 2017;Wiepking et al. 2014).
When examining the transfer of these religious traditions (beliefs and practices) between generations, evidence of religious identity and giving to a religious organization is also a predictor of children and second-generation adults' giving to secular organizations (Cooper et al. 2012;Wilhelm et al. 2008). Other research, focused on the Church of Jesus Christ of Latter-Day Saints (Mormons), also suggests lifelong religious individuals are more inclined to make external gifts than converts (Curtis et al. 2015).
The above evidence shows that religion develops norms of helping others through teachings, and affiliation into such religious groups reinforces these norms among members. Hence, those who practice religion within communities that promote empathetic responses to others are most likely to engage in giving to secular causes than those with no religion. Specifically, Neumayr and Handy (2019) argues that religiously affiliated individuals give because they are taught it is their duty to help and because they may have stronger prosocial values compared to non-religiously affiliated individuals. In addition, Ottoni- Wilhelm (2010) argues that religions that are successful in combining identity and empathy-evoking teachings with a "principle of care" are successful in promoting giving outside of one's own "ingroup", implying that identity plus norm creates a positive relation to giving to outgroup and secular organizations.

Social Network and Service Attendance
Next to religious affiliation, the second largest instrumentalization of religion's effect on external giving, in our systematic literature review, is through ties within a religious social network mainly operationalized by measuring religious service attendance in predicting giving to both religious and secular organizations. The included studies show that the community in which people are integrated for a religious purpose affects giving to outgroup and secular organizations in multiple ways. First, by attending regular religious services, people are exposed to more information about secular causes through announcements, volunteer opportunities, or religious teaching Carabain and Bekkers 2011). Second, service attendance also leads to the frequent solicitation of funds during ritualized giving practices. Third, there are often explict opportunities through religious teachings and commitments to establish greater empathy towards both ingroup and outgroups (Ottoni-Wilhelm 2010). Fourth, there are psychological reasons attached to service attendance and giving; people learn to give out of self-signaling (aiming at a social reward), self-affirmation, or the identification and empowering the self through what the religion teaches Cheung and Kuah 2019). Moreover, empirical studies find that the moral foundation-specifically fairness/reciprocity-and the importance of faith to the believer are the mechanisms through which service attendance affects secular giving (Shepherd et al. 2019;). This could be because those with a strong moral foundation and who ascribe a greater importance to faith attend religious service more frequently compared with those who consider faith as less important in their daily lives.
However, the included studies find contradicting evidence of the effect of religious service attendance on giving to non-religious purposes. While some find a positive effect, others show negative or insignificant effects. Yet the results are dominantly positive and significant. These variations are dependent on the geographical focus, the religion studied, the level of attendance, and the type of secular giving measured. In their study within the Netherlands, Carabain and Bekkers (2012) found that attendance has a positive and significant effect on Christians giving to secular causes, a significantly negative effect for Muslims, and an insignificant effect for Hindus. Lyons and Nivison-Smith (2006) show that only a moderate level of attendance increases giving to civic organizations compared to high or low attendance in Australia. Moreover, Mersianova and Schneider (2018) found that in Russia, attendance increases giving to only two secular causes-poverty and victim support causes, whereas Sansani and Rozental (2018) found that religiosity in Israel decreases the probability and amount of giving to gay charities. Shepherd et al. (2019) note that not all attendance is equal. Ottoni- Wilhelm (2010) found that attendance had different effects among different religious denominations, whether evangelical Christian, mainline Protestant, or Catholic. In addition, an individual's concept of God moderates the effect of their religious attendance. The more an individual has a traditional God concept, the more his or her religious attendance is associated with higher levels of the fairness/reciprocity foundation, which in turn leads to higher outgroup giving.
In addition to service attendance, other forms of social networking can be used to predict giving trends. Schnable (2015), using the 2005 Global Issues Survey data, found that the participants with close friends within their congregation reported an increase in giving. Congregations with a high number of immigrants, as well as those who have hosted a missionary or international speaker, reported an increased donation to international causes. Furthermore, studies show that other variables such as age, education, employment status, gender, partner's religiosity, parental giving to both religious and secular organizations, and income correlate with religiosity variables determine the effect of religion on external giving (Diop et al. 2018

Private Rituals
Religious practice, including both public (e.g., membership and attendance in a faith community) and private (e.g., prayer and meditation), are dimensions of religiosity (Reitsma et al. 2006). We admit that religiosity measures such as identity, values, norms, and service attendance alongside private ritual practices are highly correlated and difficult to separate. Yet, our studies note enough distinctions between these categories to require a third independent mechanism, as these studies found contradictory results in how prayer-as the most commonly measured private religious ritual-affects giving to the outgroup (Diop et al. 2018;Greenway et al. 2018;Thunstrom 2020). Thunstrom (2020) shows there are actually two mechanisms in how prayer affects giving using experimental design. The first way is the substitution effect-where prayer is viewed by religious individuals as making a change in the lives of the people they are praying for. Therefore, prayers are sometimes a substitute for charitable donations. The second explanation is an empathy effect where people tend to consider someone in need while praying, which leads them to increase their donations. Thus, in analyzing studies that used prayer as a way of explaining the effect of religion on charitable giving, we need to evaluate which mechanism is at work-substitution or empathy-and determine its positive or negative impact on external giving.
For example, while there could be an assumption that performing daily rituals such as prayer (in private) serves as a key religious practice and may be associated with increased prosociality, Greenway et al. (2018) found the contrary. Using an experimental design assigning 313 Christian participants either to intercessory prayer or secular thought (meditative thought that is not religious) on the hardships faced by Christians (ingroup) or Muslims (outgroup) in Myanmar/Burma being persecuted by the Buddhist majority, the study found that participants given prayer conditions donated money less often than the participants in secular thought conditions. Therefore, this third mechanism-and specifically the substitution effect-can explain the results that associate prayer with less monetary donations. Greenway et al. (2018) also found that those participants who were assigned the prayer condition to ingroup members gave more than those who were assigned to pray for outgroup communities.

Discussion and Conclusions
In this study, we have plotted the existing knowledge on the effect of religion on giving to outgroup and secular organizations at the individual level. We have synthesized results from empirical studies and arranged the underlying theoretical explanations and mechanisms at work in a consolidative conceptual model. Our systematic literature review, covering 77 studies, reveals that religion-measured as group affiliation, values, beliefs, and the importance of faith to the believer, as well as religious service attendance and private prayer-most often positively relates with giving to outgroup and secular organizations. Our finding is contrary to some studies that strictly argue that religion has no effect on prosociality because of social desirability effects, as most of the studies on the topic use self-reported religiosity and giving scales (Galen 2012). In contrast to this argument, we found dominantly positive effects even among experimental studies. Nonetheless, we also found other studies that show a negative or insignificant effect of religion on external giving. Such variation mostly appears to depend on the type of religion studied, the geographical focus of a study, the methodology followed, how religion is measured, and the type of secular organizations studied.
In investigating the relationship between religion and giving to outgroups and secular organizations, we have identified three main theoretical and empirical mechanisms explaining how religion affects external giving. Each mechanism has various pathways through which religion may act. Two of these mechanisms propose a strong positive relationship between religion and external giving, namely the theory of identity and norm through affiliation, and social networking through service attendance. The identity and norm theory argues that most religions teach followers to help others both inside and outside their own religious traditions. Through such teachings, religion imparts a giving behavior and creates the norm of giving to its followers. However, such a positive relationship is still dependent on the focus on the type of religion and geographical location. We found some indications that even similar religions may have different norms in various geographical contexts.
Second, through integrating into the community and practice of a particular religious group and frequently participating in religious service attendance, individuals are increasingly exposed to religious teachings, more solicited, and face greater psychological effects, such as self-signaling for good behaviors for social reward purposes that, in turn, increase giving. Here, attendance also provides different results depending on the country, type of religion, and denominational focus of a given study. Third, through private rituals such as prayers and how individuals understand prayers-with prayer itself as philanthropic help (substitution effect) or as a reminder to extend further help (empathy effect)-the third mechanism can have both negative and positive impact.
In addition, the studies included in this research also mention other moderating and important variables that affect the relationship between religion and external giving. For example, the specific conceptualization of God-measured in terms of individual understanding and belief about God-can moderate the relationship between attendance and giving to outgroups. If an individual demonstrated a strong, traditional God-concept, we could likewise expect a higher degree of both religious attendance and higher levels of the fairness/reciprocity moral foundation that is associated with a higher outgroup giving. Additional crucial variables include age, education, employment status, gender, partner's religiosity, parents' religious and secular giving, and income. These variables also determine the individuals' giving behavior to outgroup and secular organizations.
While religion remains one of the major determinants of giving, it is often criticized for limiting resources within the ingroup among fellow religious practitioners (Turner 2005). Identifying the underlying mechanisms and moderating variables is key to understanding how religion affects external giving. For example, individuals may only give to a particular type of secular organization that complies with their norms, values, and beliefs. In addition, by praying for others, including outgroups and the world in general, religious people might be extending help beyond their own religious group. By attending religious services regularly, religious people might be giving to religious purposes regularly and may have limited resources to give to other external organizations. This implies that the relationship between religious giving and secular giving also needs to be evaluated extensively, as sometimes these two factors may be conditioned by a substitutionary effect . We also want to pose the following question: if religious individuals give to their own congregation, and the latter, in turn, actively engages in social welfare, should this also be interpreted as external giving by itself? The category of secular giving by itself remains problematic because, unlike congregations and denominations that are solely religious, there are many organizations classified as secular in purpose but maintaining a religious identity. Introducing such organizations in the analysis may bring a different picture to the relationship between religion and secular giving. If individuals are giving to faith-based organizations that are in line with their individual identities and norms, and if such faith-based organizations extend help to a larger society, is this not external help?
By configuring the mechanisms through which religion affects external giving, our conceptual model enables further research to consider underlying mechanisms to design their empirical approach. Only if we know what mechanism we are examining can we then determine which mechanism might be most operational in the results that we find. Moreover, future studies can build on our work to come up with additional mechanisms, as our study remains a literature review limited to a specific database search. We did not include retrospective and prospective reference checking for the included studies that meet our criteria. Given that we identified more than 2000 studies from the two top databases in religion and social science studies, we think that we have included important studies that show the significant mechanisms at work in explaining the relationship between religion and external giving. Finally, our study is limited to monetary donations, and the models we propose might not explain the giving of time and other material resources. Future research can also explore the relationship between religion and the giving of time and material resources to outgroups and secular organizations and how this differs from giving of money.
Author Contributions: K.I.Y. made substantial contributions to the original conceptualization and design of the project; provided keywords; conducted the literature search and screening, and read and re-read half of the articles included in the study; she also contributed to developing the model, writing the significant part of the analysis of the results, discussion, and conclusion of the study. A.G.A. assisted in the conceptualization and design of the project; provided keyword for literature search, screened half of the articles found from the database search, read and re-read half of the articles included in the study, and contributed to writing part of a result section and editing the entire document; D.P.K. assisted in the conceptualization and design of the project; and provided revisions to the model, organization and substantive content of the article. All authors have read and agreed to the published version of the manuscript.
Funding: This research was funded by the University of Notre Dame grant number 262164IUPUI, as part of the Global Religion Research Initiative, which is part of a larger grant award from Templeton Religion Trust of Nassau, Bahamas: grant number TRT0118.      However, the interviews explored that Muslims also feel a duty to give to God NA Note: Religion All refers to at least all the Big Five religions; (ns.) means not significant, whereas sig implies the coefficient is significant; NA represents not applicable. In addition to the above empirical studies, this systematic literature review also includes theoretical studies including Atkinson (2016)

Appendix B
Criteria for considering studies

Appendix B
Criteria for considering studies  Studies must be individual level analysis  Studies must examine the effect of religion on secular giving  We also included studies that used religion as a control variable to predict giving to secular organizations  Studies should primarily focus on monetary donations. Studies whose primary focus is on volunteering or any other type of prosocial behavior other than providing money to nonreligious helping purposes or giving to secular non-profit organizations are not included.  We include studies where the measure of religion is different, such as religiosity and spirituality, religious attendance, religious affiliation, etc.  Studies that discuss the effect of the five major religions (Hinduism, Judaism, Buddhism, Islam, and Christianity) on secular giving are also included  Studies must consider secular giving as giving solely to non-religiously affiliated institutions, for non-religious purposes (giving to any of the NTEE subsectors except religion is included)  Giving to outgroups should measure the donations intending to benefit individuals outside of one's religious group.  Studies can also discuss different denominations within the five major religions  Studies must be written in English  No exclusion criteria on the time of publication  No exclusion criteria regarding the study design or methodological approach (qualitative and/or quantitative empirical studies, as well as theoretical work, will be considered)  No exclusion criteria concerning the source (peer-reviewed journals, books, book chapters, journals without peer review as well as unpublished articles and grey literature will be considered) (Amankwaa and

Studies must be individual level analysis
Religions 2020, 11, x FOR PEER REVIEW 21 of 25

Appendix B
Criteria for considering studies  Studies must be individual level analysis  Studies must examine the effect of religion on secular giving  We also included studies that used religion as a control variable to predict giving to secular organizations  Studies should primarily focus on monetary donations. Studies whose primary focus is on volunteering or any other type of prosocial behavior other than providing money to nonreligious helping purposes or giving to secular non-profit organizations are not included.  We include studies where the measure of religion is different, such as religiosity and spirituality, religious attendance, religious affiliation, etc.  Studies that discuss the effect of the five major religions (Hinduism, Judaism, Buddhism, Islam, and Christianity) on secular giving are also included  Studies must consider secular giving as giving solely to non-religiously affiliated institutions, for non-religious purposes (giving to any of the NTEE subsectors except religion is included)  Giving to outgroups should measure the donations intending to benefit individuals outside of one's religious group.  Studies can also discuss different denominations within the five major religions  Studies must be written in English  No exclusion criteria on the time of publication  No exclusion criteria regarding the study design or methodological approach (qualitative and/or quantitative empirical studies, as well as theoretical work, will be considered)  No exclusion criteria concerning the source (peer-reviewed journals, books, book chapters, journals without peer review as well as unpublished articles and grey literature will be considered) Studies must examine the effect of religion on secular giving

Reference
Religions 2020, 11, x FOR PEER REVIEW 21 of 25

Appendix B
Criteria for considering studies  Studies must be individual level analysis  Studies must examine the effect of religion on secular giving  We also included studies that used religion as a control variable to predict giving to secular organizations  Studies should primarily focus on monetary donations. Studies whose primary focus is on volunteering or any other type of prosocial behavior other than providing money to nonreligious helping purposes or giving to secular non-profit organizations are not included.  We include studies where the measure of religion is different, such as religiosity and spirituality, religious attendance, religious affiliation, etc.  Studies that discuss the effect of the five major religions (Hinduism, Judaism, Buddhism, Islam, and Christianity) on secular giving are also included  Studies must consider secular giving as giving solely to non-religiously affiliated institutions, for non-religious purposes (giving to any of the NTEE subsectors except religion is included)  Giving to outgroups should measure the donations intending to benefit individuals outside of one's religious group.  Studies can also discuss different denominations within the five major religions  Studies must be written in English  No exclusion criteria on the time of publication  No exclusion criteria regarding the study design or methodological approach (qualitative and/or quantitative empirical studies, as well as theoretical work, will be considered)  No exclusion criteria concerning the source (peer-reviewed journals, books, book chapters, journals without peer review as well as unpublished articles and grey literature will be considered)