The word ‘religiosity’ is interpreted in a variety of ways, and its meaning is interdisciplinary. It is not surprising that Gill et al. (2010) recognised that religiosity is a difficult term to define, which has resulted in numerous definitions and models of meanings for the word. This shows that the topic of religiosity cannot be studied solely to identify one aspect of its meaning (Gill et al. 2010). Villani et al. (2019) recognised the complexities of religiosity, prompting her to propose 13 items to comprehend its meaning according to the constructs of commitments, in-depth exploration and reconsideration of commitments. Gill et al. (2010) presented 13 items as the dimensions of religiosity, which generally refer to identity commitments, including a specific religious worldview. Holdcroft (2006) agreed that religiosity is a complex concept to define, at least for two reasons: (1) the uncertainty of the meaning of the root word ‘religiosity’, particularly in English, and (2) the approach to religiosity, which is multi- and even interdisciplinary due to the significant interests of scholars in studying religiosity across academic fields. These two factors also become the markers for why the dimensions of religiosity differ. Because there are various definitions for religiosity, there has been extensive studies on this subject.

Religiosity is a psychological phenomenon. Hence, it cannot be understood solely by identifying one dimension. It is not surprising that social and psychological scholars offer a variety of scales and items for assessing religiosity (Hill & Hood 1999). In this context, Abdel-Khalek and Lester (2017) defined religiosity as:

Abdel-Khalek and Lester (2017) emphasised that religiosity refers to a system of personal beliefs, values and various religious practices. People require a belief system as a reference for a better life. This results from the transcendence process or the formal and informal institutionalisation of religious doctrine. It necessitates a strong understanding of experience, mental aspects and individual appreciation of the belief system that is embraced and firmly believed. This type of transcendence process becomes a psychological phenomenon. In addition, Iddagoda and Opatha (2017) identified that religiosity has dimensions such as orientation, behavioural set and lifestyle that are considered important by every community and accepted socially or personally. Thus, the dimensions of orientation, behavioural set and lifestyle are identified as the components of religiosity.

A set of brief information on various perspectives toward religiosity is shown in Table 1. Such studies provide a brief information on a variety of perspectives on religiosity. Joshanloo (2021) assessed religiosity using three questions: (1) ‘Regardless of whether you belong to a specific religion, how religious would you say you are?’; (2) ‘Aside from special occasions like weddings and funerals, how frequently do you attend religious services nowadays?’; (3) ‘Aside from religious services, how often, if at all, do you pray?’ These three questions address the dimensions of ‘level of religiosity’, ‘frequency of participation in religious services’, and ‘frequency of prayer performed’. Joshanloo’s (2021) dimensions are used to comprehend the impact of religiosity on life satisfaction. However, religiosity in this study is positioned as a variable that modifies and positively affects ‘life satisfaction’. It indicates that religiosity can dynamically mediate between the variables ‘positive effect of emotion’ and ‘life satisfaction’.

Ten Kate, De Koster and Van der Waal (2017) differed from Joshanloo (2021) in that they attempted to identify the direct effect of religiosity on life satisfaction, even with different dimensions of religiosity. They defined religiosity in two dimensions before examining its impact on life satisfaction. The first dimension is religious beliefs. A spiritual person’s character is to adhere to religious beliefs, which can become the foundation for interpreting the empirical world and how individuals act and behave correctly in their lives. The second dimension is private religious practices. Theoretically, religious practice in private settings is a dimension of religiosity that can play a role. In accordance with this, Zotti, Speziale and Barra (2016) performed the same steps and studies on the effects of religiosity on life satisfaction. They discovered that there is empirical evidence that an individual’s level of religiosity directly influences life satisfaction. These different variables (i.e. religious attendance and religious beliefs) associated with religiosity confirm one thing: the heterogeneity of religiosity dimensions used in one study is highly dependent and determinant with the endogenous variable (i.e. a dependent variable) that will identify the influence of religiosity on it. The relationship between religiosity and life satisfaction must be understood in this context.

Religiosity in several studies is assessed as the influence of religion (Mohd Dali et al. 2019). This confirms an assumption that religiosity is highly dependent on the underlying religion. Thus, religiosity among Islam, Christianity, Buddhism, and Hinduism tend to be different because of the differences in the doctrines and beliefs in those religions. In Islam, Manurung (2014) identified that religiosity refers to consistent reflection and appreciation of Islamic values (Manurung 2014). In addition, religiosity in Islam refers to the fundamental awareness that human life today is only an instrument to achieve happiness in the hereafter, so that Muslims must perform good deeds (Anita, Kartowagiran & Ayub 2019). Thus, Islamic religiosity refers to ‘the extent of the strength of faith, the belief of a Muslim in which the dogma is practiced daily’ (Ajuna 2021).

Meanwhile, religiosity in the Christian tradition refers to the theological awareness based on the Trinitarian structure. This awareness encourages the belief that God is the creator of the universe. This faith must be practised and reflected in the daily behaviour of Christians (Hons 2010). Köllner (2020) identifies that religiosity in the Christian tradition refers to ‘practical theology that manifests in the worship of the saints and daily prayer in living life’ (Köllner 2020). The meaning of religiosity in two religions, namely, Islam and Christianity, shows the existence of theological awareness and is manifested in the daily behaviours of Muslims and Christians. Thus, a strong faith in God (i.e. Allah and Jesus) is reflected in various aspects of their life.

Meanwhile, religiosity in Buddhism has been identified by Verma (2020), as having several dimensions – from the theological realm to the appreciation of the values of Buddhism in everyday life. The Buddhist values are fully described in the Eight-Fold Path and the Lotus Sutra. It is just that religiosity in Buddhism is practiced differently among Buddhist schools. There are at least three schools of Buddhism, and they influence the meaning of religiosity practised by Buddhists. They are Theravada, Mahayana and Vajrayana (Verma 2020). In the Theravada school, it is recommended to heed the advice of sages, remember that advice and evaluate individual experiences and practices. The Theravada path begins with study, is followed by training and culminates in the attainment of Nirvana (Gombrich 1988).

In contrast to the Mahayana school, which emphasises the triumph of the Bodhisattva by opening the way to Buddhahood, the Vajrayana school believes that self-nature (human nature) is Buddha nature (the essence of the seed of Buddhahood). To attain Bodhisattvas, Buddhists need a qualified teacher whom the leaders of the four schools recognise: Nyingmapa, Sakyapa, Kagyudpa, and Gelugpa. In addition, qualified instructors teach total surrender of body, speech and mind and advise to take refuge in the Buddha, Dharma and Sangha (Gombrich 1988; Verma 2020). Buddhists can show high religiosity in everyday life with such beliefs and doctrines.

Religiosity in the Hinduism tradition has been identified by Baral (2020). He successfully found that religiosity in Hinduism has an intrinsic and extrinsic character. In this context, there are at least four kinds of Hindu religiosity: (1) ritualism: refers to Vedic-Brahmanistic ritualism, which is domestic and requires sacrifice, but does not include some forms of Tantrism; (2) spiritualism: intellectual piety, aimed at seeking freedom (moksa) for the individual, usually with the guidance of a teacher. This is characteristic of Advaita Vedanta, Saiva Kashmir, Saiwa Siddhanta, Neo-Vedanta, Esoteric Guruism and some kinds of Tantrism; (3) devotionalism: is the worship of God, as emphasised in the Bhakti and Krishna traditions and (4) heroism: a form of polytheistic religiosity stemming from militaristic traditions, such as Ramaism and parts of political Hinduism. It is also called wirya-marga (Baral 2020; Ramachandran 2018). The previous descriptions related to religiosity in Islam, Christianity, Buddhism, and Hinduism show different features of religiosity. This is due to the various scriptures and doctrines that form the foundation of religiosity in every religion.

Maddux (2018) defines life satisfaction simply as a feeling of happiness and becoming satisfied with life. There are two keywords from the meaning proposed by Maddux (2018), namely, happiness and well-being. Individuals who are considered satisfied with life feel happiness and a sense of well-being. In this case, Toker (2012) understands life satisfaction as ‘the degree to which a person positively evaluates the overall quality of the life as-a-whole’. This confirms that life satisfaction is subjective and personal, whereas individual satisfaction with life differs. Therefore, a universal standard of life satisfaction is needed (Lambert et al. 2009). In this context, Brown and Duan (2007) proposed predictors of life satisfaction, including individuals’ demographics, psychological characteristics and life experiences. The proposal offered by Brown and Duan (2007) is not the only indicator that can predict and measure individual satisfaction with life.

Nair and Gaither (1999) identified that marital status, social support and opportunities to socialise with the environment are closely related to life satisfaction. In addition, indicators such as health, leisure, family, work, financial situation, social relationships and self-worth were proposed as other indicators related to life satisfaction on a scale that is more often referred to by social scholars (Milovanska-Farrington & Farrington 2021). Na-Nan and Wongwiwatthananukit (2020) suggested several indicators that are rarely considered by other social scholars, related to life satisfaction. According to them, there are at least five important indicators related to life satisfaction, namely, (1) enthusiasm to do activities and attention to one’s own living conditions; (2) resolution and fortitude as the acceptance of life values; tolerance of problems encountered in life and perception to problems as experience and learning resources; (3) compatibility between the desired and achieved goals as an indicator of success in life; (4) self-concept refers to satisfaction with one’s health, and contributing meaningfully to society; (5) mood regulation as a means of knowing how to be happy, having a good attitude and positive emotions towards other people and the environment, and the ability to overcome sad events (Na-Nan & Wongwiwatthananukit 2020). Various indicators related to life satisfaction have been proposed. Although they differ from one scholar to another, two keywords can unite these differences and are agreed upon as the main indicators of life satisfaction: ‘happy’ and ‘well-being’. Thus, individual life satisfaction can be described as the feeling of happiness possessed by individuals when they achieve the desired level of well-being.

Tikito, El Arass and Souissi (2019) asserted that to conduct a meta-analysis, four aspects must be considered: information source, technology, method and impact. These aspects must be considered because they serve as the foundations for producing a quantitative analysis of the existing literature through meta-analysis. According to Israel and Richter (2011), because meta-analysis is a statistical technique used to combine several published studies, the data collected must be in the form of literature, that is, journal articles, working papers and research reports that can be accessed openly online. Referring to the model used by Tikito et al. (2019) and Israel and Richter (2011), the study applies a data collection model with two approaches, namely: meta-analysis and SLR. The criteria for the article selection process for meta-analysis included (1) data on the number of samples (N), R Square values and the countries where the studies were conducted; (2) descriptive statistical information in the form of the mean value of each variable and (3) full articles published in journals. Twenty-one articles were chosen based on these three criteria to be analysed using a meta-analysis approach. Following the meta-analysis, data were collected for conducting SLR to map issues and study directions related to the influence of religiosity on life satisfaction.

According to Okoli (2015), the SLR approach identifies specific literature relevant to the study’s objectives. Following the establishment of the article selection criteria, the researchers synthesised the methodology employed in each article and the theoretical arguments advanced by previous researchers. This was done because SLR, as a method, essentially assists and allows researchers to develop theories through a review of previously published literature (Nomran & Haron 2019; Okoli 2015). In this regard, this study chose 21 articles based on the following criteria: (1) the article had a full version and was published in a journal; (2) the selected article was a study that investigated the influence of the variables of religiosity on life satisfaction and (3) the article could be accessed primarily through the databases of Google Scholar and Science Direct. It is hoped that using these procedures and criteria, the issues of religiosity and life satisfaction can be mapped out from the published literature.

This study employed two data analysis models: data analysis using a meta-analysis approach and data analysis using SLR. This study employed a comprehensive meta-analysis to examine the effect of religiosity on life satisfaction (Al-Wasy 2020). Stata 16.0 software was used to aid in the analysis. Data such as correlation coefficients and sample sizes were used to calculate the effect sizes of religiosity on life satisfaction (Leong et al. 2021). Moreover, the data analysis using the SLR approach was performed through a consistent and critical analysis of the characteristics and issues contained in the literature related to religiosity and life satisfaction. This procedure was used to map the variables and indicators used in the existing literature on the influence of religiosity on life satisfaction (Ahmad & Omar 2016). In the end, the mapping process served as the foundation for determining the direction of studies on religiosity and life satisfaction.

This study employed a meta-analysis approach to 21 articles concerning the effect or influence of religion on life satisfaction. Hence, these criteria became the foundations for omitting the articles that did not meet the standards and selecting those conforming to the requirements for executing meta-analysis. These articles were found by searching the Google Scholar database. The journals in which the articles were published were then determined (Israel & Richter 2011). Eighty-five percent or 17 articles examined were classified according to the first selection criterion. The articles had been published in reputable international journals indexed by Scopus. The remaining 15% of the articles were published in journals that Scopus did not index.

In the other aspect, such as the number of samples, the articles chosen were fairly diverse. The sample sizes were small, but they met the requirements for analysis. For others, the sample sizes were quite large. Samples came from a variety of countries, not just one. Three studies used very large examples of data, all of which used data from the World Values Survey. Moreover, the countries where the researchers collected the samples were relatively diverse, i.e., Indonesia, Iran, Korea, the US, Peru, Greece, and Australia. Asia, the Americas and Europe were all represented. This confirmed that the studies were carried out in various locations, with relatively high sample heterogeneity. Because the samples were drawn from different countries, it could be concluded that the samples were also heterogeneous in terms of demographics and not homogeneous. The heterogeneity of such samples is critical in quantitative studies to draw robust conclusions (Tikito et al. 2019). The samples used by 21 articles in the selected studies could be considered a very high variation of samples. Therefore, they already met the representative sample criteria (Creswell 2013). It meant that the samples could represent the population and different studies on the same issue.

Table 2 summarises the four aspects of the articles investigated in the meta-analysis. These aspects include authors and years, locations, method and the number of samples used. Based on the information displayed, it is clear that the 21 studies chosen were diverse and heterogeneous. The heterogeneity was identifiable from the varieties of study locations in various countries. Similarly, the methodologies used by the 21 studies varied although the linear regression approach was dominant in general. Another factor that varied greatly among these studies was the number of samples used. Faheem et al. (2019) conducted a study with a minimum sample size of 80 samples. The largest sample size was obtained in a survey conducted by Plouffe and Tremblay (2017) that included 85 072 samples. Thus, although there were only 21 articles chosen for this study, the articles met the criteria for study representation. However, the papers had represented the existing studies (Tikito et al. 2019) by the degrees of site heterogeneity, method and sample number. Considering the information in Table 2, incorporating the 21 studies into the meta-analysis was feasible and conceivable.

Table 3 provides several statistical aspects of the existing studies related to religiosity and life satisfaction, which could be interpreted differently. Firstly, this study had a relatively small number of articles selected, but these articles were sufficient and met the meta-analysis standards. The preceding was indicated by the significant value of the homogeneity test (0.0000). Thus, because the Q value was statistically significant, all included studies could be synthesised (Kulinskaya, Dollinger & Bjørkestøl 2011). Secondly, the heterogeneity value, when using the ‘random effect’ method to combine the effect quantity, was significant (p < 0.00). This demonstrated heterogeneity, so the results of meta-regression on religiosity could explain the heterogeneity among effect sizes (Kulinskaya et al. 2011). Thirdly, Figure 1 indicates that the influence of the religiosity variable on life satisfaction was significant in various study settings. This was demonstrated by the effect size overall statistical value of 2.85 (effect size with 95% CI). This confirmed that the influence of religiosity on human life satisfaction was very contributive and significant (Lim & Putnam 2010; Ten Kate et al. 2017). The meta-analysis approach used in the studies on the effect of religiosity on life satisfaction confirmed a theoretical belief that the religiosity variable is a powerful variable that explains and even influences human life satisfaction in various aspects. This is undoubtedly an impetus for academics to continue researching variations in the influence of religiosity on the elements of human life satisfaction. It seems necessary to chart the evolution of religiosity issues and their impacts on life satisfaction in this context.

For decades, social scientists have researched religiosity and its relationship to human life satisfaction. Until now, such studies have grown in tandem with the growing interests of interdisciplinary scholars in identifying the dimensions of religiosity and their influences on various aspects of human life satisfaction. Several categories for the effect of religiosity on human life satisfaction could be determined from the existing studies in the following ways: firstly, identifying life satisfaction through the influence of theological dimensions on religiosity (Barro & McCleary 2003; Hill & Hood 1999; Strulik 2016; Witzig & Alec Pollard 2013); secondly, identifying human life satisfaction due to religious beliefs, rituals and practices (Ammerman et al. 2019; Lim & Putnam 2010; Platsidou 2013) and thirdly, identifying the influences of religiosity dimensions, which were formed through the appreciation of theological aspects and religious rituals, on human life satisfaction (Bomhoff & Siah 2019; Joshanloo 2021; Przepiorka & Sobol-Kwapinska 2018). These three categories were dominant and easily identified in the existing published studies. They all viewed religiosity as a determining factor that influenced and shaped people’s perceptions of life satisfaction.

Table 4 lists three issues concerning religiosity and its relationship to life satisfaction. Based on the sources that comprised the two variables, the developed categories referred to the meaning of religiosity and life satisfaction (Ammerman et al. 2019; Lewis et al. 1996). In terms of religiosity, two sources contributed to an individual level of religiosity: theological awareness and appreciation of religious teachings or dogmas (El-Menouar 2014). The existing studies gave rise to three conceptual types in formulating the construct of religiosity during its development. Some studies interpreted religiosity only in terms of theological awareness, so the indicators chosen included all forms of beliefs in transcendental things, such as God, hell, and heaven (Clark & Lelkes 2011; Kongarchapatara et al. 2014; Park et al. 2012). Other scholars interpreted religiosity based on the consistency of religious rituals, such as religious service attendance, membership in religious organisations and prayers (Ayten & Korkmaz 2019; Kıraç 2016). The third typology of studies on religiosity was the one that viewed religiosity as the result of both theological and ritual appreciation (Carranza Esteban et al. 2021; Fard et al. 2013; Ten Kate et al. 2017). It means that a religious person can integrate transcendental beliefs and practise them as rituals in social, political and economic life.

The construct of life satisfaction was also built up in various ways (Okulicz-Kozaryn 2009; Villani et al. 2019). However, the dimensions of life satisfaction developed by scholars could be classified into several criteria, namely, (1) material criteria, which included satisfaction at the economic and social levels, that is, life satisfaction as measured by satisfaction with marriage, prosperity, descendants and social support (Kıraç 2016; Ten Kate et al. 2017), and (2) satisfaction in psychological criteria, such as happiness or life satisfaction included in the scale with life satisfaction (SWLS). This scale included life satisfaction at the psychological level (Clark & Lelkes 2011; Yeniaras & Akarsu 2017). However, various studies on religiosity and individual life satisfaction remain to be conducted. This is because religiosity issues keep evolving along with the development of human life.