Workplace Social Capital: Redefining and Measuring the Construct

Although workplace social capital (WSC) is a relevant construct that contributes positively to employee and organizational wellness, there is lack of consensus regarding its definition and measurement. The aim of this paper was to synthesize a valid definition of WSC and develop an instrument measuring the construct. Based on a literature review of existing definitions (Phase 1), we conceptualized WSC as a workplace resource that concerns employees’ perceptions regarding trust, reciprocity (cognitive WSC), and network interactions (structural WSC) that exist among peers (bonding WSC) and among individuals across hierarchical levels and organizations (bridging WSC). Next, we developed the WSC Inventory (WoSCi; Phase 2) and, we tested the psychometric properties of the new scale (Phase 3). The initial structure of the scale was explored in a sample of university employees (N = 376). Multilevel confirmatory factor analysis in a heterogeneous sample of 733 employees nested in 158 work groups supported the hypothesized factor structure of the WoSCi. Results also supported the internal consistency, as well as the convergent, criterion-related and incremental validity of the WoSCi in explaining work engagement, burnout, job performance over and above similar constructs, such as individual social capital and psychological capital. These results highlight the relevance of WSC as defined and measured with the WoSCi and underline its value for explaining work-related well-being and organizational behavior.


Introduction
Social capital (SC) refers to those elements of social interactions and structures that act as resources since they facilitate action leading to favorable outcomes for individuals, groups, and the society (Ferlander, 2007). In the work context, workplace SC (WSC) is more commonly conceptualized as an ecological resource that resides in the organization and generally refers to certain features of organizational life that facilitate employees to collaborate effectively in pursuing shared organizational goals (Putnam, 1995). Accordingly, the central features of WSC are trust (i.e., expectation for honest and reliable behavior; Fukuyama, 1997), norms such as reciprocity (i.e., mutual exchange of support and benefits; Harpham et al., 2002) and network interactions (i.e., creating, expanding, and utilizing interpersonal relationships; Gibson et al., 2014) that exist and are developed among organizational members but also across organizations. Approaching WSC as an ecological resource is particularly relevant for organizational life, since WSC as a contextual characteristic, may be subject of interventions aiming at enhancing optimal employee and organizational functioning. Through its capacities, WSC may benefit organizational life by impelling employees to engage in collective behavior, and by providing access to further resources (Adler & Known, 2002). Indeed, literature suggests that WSC relates positively with job satisfaction (Ommen et al., 2009) and work engagement , and negatively with emotional exhaustion (Kowalski et al., 2010) and job stress (Firouzbakht et al., 2018).
Despite the growing interest in the role of WSC for employee and organizational wellness, there is lack of consensus when it comes to its definition and measurement (Oksanen et al., 2013). As concerns its definition, several conceptualizations have been proposed in the literature, but these approaches seem to disagree about what WSC is. Specifically, some approaches neglect or undermine core aspects of the construct such as, reciprocity (Petersen et al., 2010) or networking (Ommen et al., 2009), while others incorporate facets (e.g., justice; Pejtersen et al., 2010) that are related but distinct from WSC (Kreuter & Lezin, 2002) or equate WSC to similar constructs (e.g., social support; Lin, 2001). All these, blur the uniqueness of construct. Additionally, in some approaches, core, distinct dimensions are merged (e.g., trust and reciprocity; Kouvonen et al., 2007), or not clearly defined (e.g., networking aspects are confused with social norms; Ommen et al., 2009). Moreover, often the direction of social action (i.e., inward/outward) is not clearly indicated. This lack of agreement about how WSC is defined is problematic because, as Adler and Known (2002) argue, the excessive use of WSC as an umbrella construct that integrates numerous aspects without clarity damages its theoretical and empirical relevance. This limits the theoretical development of the construct because it does not provide a valid and coherent conceptualization of what WSC is, how it differs from other constructs, and whether it adds value in explaining relevant phenomena in organizational life.
Logically, this lack of consensus is also evident in the existing tools measuring WSC that vary significantly when it comes to the different dimensions captured, and the levels at which it is assessed. For example, some scales do not capture WSC' s core dimensions (Ommen et al., 2009;Pejtersen et al., 2010) or do not capture social interactions among individuals from different levels of hierarchy (e.g., subordinates and supervisors; Eguchi et al., 2017). Others include aspects that are closely related, yet distinct Pejtersen et al., 2010) or concern only complex organizations . Finally, most scales fail to clearly distinguish between the different dimensions of the construct (Kouvonen et al., 2007;Ommen et al., 2009). This lack of consensus in the measurement is also problematic for empirical reasons, since most tools assess some but not all of the construct's core components. This means, that it is not possible to make robust comparisons of findings of different studies that measure WSC in different ways, which also limits the conclusions that may be drawn about the relevance of WSC for organizational life.
To address this lack of consensus when it comes to the definition and measurement of WSC, the main aims of our study are to synthesize an integrated definition of WSC as an ecological resource and to develop a tool for its measurement based on this integrated definition. To this end, we carried a study in three phases. In Phase 1, we conducted a literature review to specify the structure and unique dimensions of WSC with the aim to synthesize a definition that captures the core and unique aspects of the construct and allows distinguishing it from other related yet distinct constructs. In Phase 2, we used the updated definition of WSC to develop the Workplace Social Capital Inventory (WoSCi) to measure the construct. In Phase 3, we tested the psychometric properties of the new scale. Namely, we explored its initial factor structure, we confirmed the scale's factor structure by means of multilevel confirmatory factor analyses (MLCFA), that allows accounting for the potential interdependency between employees and their work groups when assessing WSC, we test its internal consistency, and its convergent, criterion, and incremental validity over and above other forms (individual and psychological) of capital.
By addressing these goals, we add to the literature in the following three ways. First, we contribute to the theoretical development of the WSC construct by synthesizing a definition that highlights its unique dimensions and levels of measurement. This is relevant because it enhances the construct's clarity and allows for a better understanding of its nomological network. Second, we add to the measurement of WSC by developing and validating a scale that addresses the limitations of existing scales. With the proposed scale, we enable future research and practice to assess WSC more accurately. Third, by developing a psychometrically sound scale that is based on an integrated definition of WSC, we contribute to organization practice by offering a useful tool that allows diagnosing and thus, promoting WSC.

Phase 1: Redefining WSC
To synthesize an accurate definition of WSC, we reviewed the relevant literature and the different conceptualizations that emerged to determine its structure (i.e., levels of measurement) and dimensions.

Method
We conducted a search on MEDLINE (via Pub Med), Scopus and Google Scholar using the following keywords: ''social capital'' or ''workplace social capital'' separately or with ''definition'' or ''origins'' or ''theory'' or ''forms'' or ''dimensions'' or ''measurement''. We also included articles on SC because research on WSC is rather limited, while the two constructs are intertwined. We identified over 700 articles and book chapters. Of these, we selected 74 manuscripts based on the following criteria: 1) they concerned SC or WSC and not similar constructs (e.g., social network, social support); 2) their aim was to define (W) SC and included specific descriptions of its content and dimensions; and 3) were written English. The first and second author evaluated the inclusion of the first 50 papers independently. Results indicated an agreement of 93% that was resolved after discussion. Due to high consistency, all other manuscripts were evaluated by the first author.

Results
The literature review resulted in 26 definitions (see APPENDIX). In most cases, (W)SC was described as including both network ties and shared values, which implies that the construct must incorporate both aspects. To synthesize a validated definition of WSC, we investigated the structure and dimensionality of the construct as depicted in the different definitions. To this end, in Table 1 we present the different forms of WSC, while in Table 2 we present the unique dimensions of WSC. Identifying the different forms is important because it allows determining the levels of measurement of the construct (i.e., the proximity and the direction of social network aspects). Identifying the different dimensions is relevant for determining the unique facets of WSC.
As shown in Table 1, the construct is mainly distinguished into: (i) bonding, bridging and linking, based on the proximity of linkages between different actors (Harpham et al., 2002;Kreuter & Lezin, 2002;Szreter & Woolcock, 2004), and into (ii) structural (e.g., network size) and cognitive (e.g., trust, reciprocity and other intangible aspects), based on its components (Grootaert & Bastelaer, 2002;Harpham et al., 2002;Uphoff & Wijayaratna, 2000). Other theoretical approaches presented in Table 1 are less common Ties between individual and groups with people or organizations in position of authority and influence (Chen & Meng, 2015;Ferlander, 2007;Harpham et al., 2002;Kreuter & Lezin, 2002;Szreter & Woolcock, 2004;Woolcock & Narayan, 2000) Structural Tangible and external observed social constructions (e.g., social networks) Cognitive Intangible aspects that related to resources providing shared values attitudes and beliefs (e.g., trust) (Grootaert & Bastelaer, 2002;Harpham et al., 2002;Krishna, 2001;Nyqvist et al., 2014;Uphoff & Wijayaratna, 2000) Relational Nature and quality of relationships (e.g., trustworthiness, social networking) (Nahapiet & Ghosal, 1998) Formal Norms, procedures and relationships that include formal participation in civic organizations Informal Social relationships that are established with family, friends, colleagues, where institutional consolidation of networks is not required (Dhesi, 2000;Pichler & Wallace, 2007;Schofer & Fourcade-Gourinchas, 2001) Horizontal Ties among individuals within same groups Vertical Ties through formal hierarchical status (Colletta & Cullen, 2000;Dolfsma & Dannreuther, 2003) Positive Reciprocal social relationships with positive social impact Negative Social relationships, usually informal (e.g., fount in protecting guilds) resulting in negative social impacts (Graeff & Svendsen, 2013) Instrumental The development of social interactions and relationships aims at individual prosperity Principled The development of social interactions based on principles and ethical values (Heffron, 2001;Van Deth, 2003) Opened Social action is based on active citizenship Closed Protective and exercising closed membership aiming at individual benefits (Heffron, 2001;Van Deth, 2003) and not well-established. Specifically, in certain cases (e.g., positive/negative, instrumental/principled) the forms of SC are mixed up with its outcomes (Graeff & Svendsen, 2013), in other cases (e.g., instrumental/principled) validity is not empirically supported, while strong overlap is found between other forms (e.g., horizontal/vertical, formal/informal; Ferlander, 2007). According to the bonding/bridging/linking distinction (see Table 1), bonding WSC refers to close ties between individuals within homogeneous groups (e.g., colleagues), bridging describes the network connections amongst individuals from different groups (e.g., colleagues from different hierarchy levels or members of the organization with other social groups or organizations), and linking refers to relationships between individuals and groups interacting across formal and institutionalized authority gradients in society (e.g., governmental organizations; Kreuter & Lezin, 2002). The conceptual similarity between bridging and linking (Adler & Kwon, 2002) explains why only some theoretical approaches incorporate linking. Importantly, most approaches distinguish only between bonding and bridging, even when they measure ties between individuals and governmental or official authorities (Chen et al., 2009;De Silva et al., 2006;Harpham et al., 2002). As concerns the structural vs. cognitive distinction (Table 1), structural WSC refers to tangible and externally observed social constructions that describe network ties and linkages that give access to resources (e.g., colleagues, professional or cultural groups; Harpham et al., 2002). Cognitive WSC refers to intangible aspects like values, attitudes and beliefs (e.g., trust, tolerance and reciprocity; Grootaert & Bastelaer, 2002;Harpham et al., 2002;Nyqvist et al., 2014). Relational WSC (Nahapiet & Ghosal, 1998) is not widely used, since it largely overlaps with cognitive and structural SC (Murayama et al., 2012).
Since the distinction between bonding and bridging is the most prominent in the literature (Table1), we determined the levels of measurement (i.e., horizontal vs. vertical) of WSC on the basis of this distinction. Accordingly, bonding WSC refers to values, beliefs, attitudes, relations and procedures that take place among employees within the same level Trust Expectation for honest and mutually supportive behavior from the others (or at least not intention to harm) (Coleman, 1988;Fukuyama, 1997;Harpham et al., 2002;Lin, 2001;Narayan & Cassidy, 2001;Putnam, 1995;Woolcock & Narayan, 2000) Reciprocity Offer and raise of mutual support (the individual provides help to the others, expecting that it will be return to him/her in the future in case of need) (De Silva et al., 2006;Harpham et al., 2002;Onyx & Bullen, 2000;Ostrom, 2000) Network connections Horizontal and vertical connections between individuals, social groups and organizations (Carpiano, 2005;Lin, 2001;Nahapiet & Ghoshal, 1998;Narayan & Cassidy, 2001;Putnam, 1995)

Social cohesion
Sense of secure and coherence within the community (Colletta & Cullen, 2000;Onyx & Bullen, 2000) Tolerance in diversity Tolerance towards others regardless of biological, social and cultural differences (Narayan & Cassidy, 2001;Onyx & Bullen, 2000) 1 3 of hierarchy (i.e., colleagues), while bridging WSC describes values, beliefs, attitudes, relations and procedures that take place among employees across different hierarchy levels (i.e., employees and management) or that extend outside of the organization (Putnam, 1995). In general, bonding SC refers to procedures and social ties of people who are alike, with inward direction, that is good for ''getting by'', whereas bridging SC refers to social ties and procedures of different social groups (or individuals that belong to them), with outward direction, that is good for ''getting ahead'' (Adler & Kwon, 2002). Next, we determined the dimensions of the bonding and bridging forms of WSC based on the cognitive vs. structural distinction (e.g., Grootaert & Bastelaer, 2002). Table 2 suggests that the three core dimensions that appear in most approaches are social networks, trust and reciprocity. Looking at the operationalization of these dimensions (Table 2) vis à vis the description of cognitive and structural forms (Table 1), it becomes evident that social networks, as observed social constructions, refer to structural WSC, while intangible aspects such as trust and reciprocity refer to cognitive WSC. Thus, we argue that bonding and bridging WSC consist of both structural (i.e., social networks) and cognitive (i.e., trust and reciprocity) dimensions.
Specifically, structural WSC refers to the qualitative aspects of networking and can be distinguished on the basis of the direction of social action (i.e., inward/outward of the organization; Harpham et al., 2002). Hence, the network ties, the frequency of interaction and the quality of social relationships among colleagues capture structural WSC at the bonding level. Rather, structural WSC at the bridging level captures the procedures and possibilities to expand the professional network outside of the organization and not just among colleagues at different hierarchical levels. This is because the networking procedure at the bringing level primarily concerns an outward direction of social action that is mainly facilitated by the management and aims to benefit from the collaboration with other organizations (Balkundi & Kilduff, 2006).
Cognitive WSC refers to intangible components like norms, values and attitudes. Trust and reciprocity are recognized as core components of WSC in extant research (e.g., Clausen et al., 2019;Firouzbakht et al., 2018;, constitute the most prominent dimensions of cognitive (W)SC (e.g., Kreuter & Lezin, 2002;Narayan & Cassidy, 2001), and are dimensions that may characterize all workplaces, regardless of organizational size, type of work or employees' social characteristics. Thus, we considered these two as the core dimensions of cognitive WSC. Accordingly, trust and reciprocity among colleagues concern cognitive WSC at the bonding level, while trust and reciprocity among employees at different hierarchy levels concern cognitive WSC at the bridging level.
Based on the previous conceptual analysis, we define: WSC as a workplace resource that concerns employees' perceptions regarding trust, reciprocity (cognitive WSC), and network interactions (structural WSC) that exist both among peers (bonding WSC) and among individuals across different hierarchical levels or organizations (bridging WSC). As shown on Fig. 1, bonding and bridging WSC refer to the levels and the direction of WSC that are assessed through cognitive (i.e., trust, reciprocity) and structural (i.e., network) WSC. Although both bonding/bridging and cognitive/structural distinctions constitute forms of WSC, the former refers to the levels of measurement and the direction of social interactions (i.e., bonding refers to social ties and procedures among peers with inward direction, while bridging to social ties and interactions among employees and management or with external organizations and includes procedures with outward direction), while the latter refers to the content of WSC that can be found at both levels of measurement and it is manifested via different dimensions (i.e., trust, reciprocity, and network).

Phase 2: Scale Development
In Phase 2 we developed WoSCi based on the updated definition. Before the item generation, we discuss in more detail the limitations of the existing WSC scales spotted in the literature, which further supports the need for a new scale that is based on the updated definition (see Phase 1).

Limitations of Existing Scales
We identified five scales that measure WSC as an ecological resource. The structure of these scales together with example items are presented in Table 3. Though relevant, these scales have certain limitations. First, although some core aspects of WSC, such as trust and reciprocity, are measured by most, these are not assessed both at the bonding and the bridging levels [e.g., the scale of Eguchi et al. (2017) captures only bonding WSC]. Second, some scales include dimensions (e.g., justice; Pejtersen et al., 2010) that are not conceived as core dimensions of WSC. Third, in some cases the emphasis is given unilaterally on common values (e.g., trust; Ommen et al., 2009;Pejtersen et al., 2010) and not on network issues that constitute a key ingredient of WSC. Fourth, most scales do not clearly distinguish between different dimensions (e.g., merge trust and reciprocity; Kouvonen et al., 2007;Ommen et al., 2009). Fifth, although Meng et al.'s (2018) scale captures all aspects of WSC, it can be applied only in complex, multi-team, organizations and not in small organizations or where a clear distinction between immediate and upper management is not evident. Also, the psychometric properties of most scales raise concerns. Although the tool developed by Kouvonen et al. (2007) is unidimensional, research concerning its validation has revealed a two- (Firouzbakht et al., 2018)

Item Generation
To address these limitations, we developed a measure that is grounded on our WSC definition, following a four-step procedure. First, we generated an item pool with items obtained from the scales of Kouvonen et al. (2007) and Pejtersen et al. (2010), because these capture both bonding and bridging WSC. Also, Kouvonen et al.'s scale is the most frequently used tool in WSC research. We excluded items assessing justice from Pejtersen et al.'s scale, since justice was not found to be a core dimension of WSC (Phase 1). Moreover, the scales by Eguchi et al. (2017) and Ommen et al. (2009) were excluded due to high overlap with the selected scales. Additionally, items from Meng et al.'s (2018) scale could not be incorporated since this scale was unpublished during the item development process. However, even if we could incorporate these items, we would not result in a substantially different scale because many items overlap conceptually with the selected items, some items capture aspects like conflict management and justice that are not key features of WSC, while other items measure WSC across teams of different departments within the organization, which are suitable only for assessing WSC in complex organizations. We conducted a literature review to allocate other items measuring trust, reciprocity and network in studies that examined WSC. Through this process two more items were selected: one from the scale of Oxenstierna et al. (2008) that evaluates respect between colleagues, and one from Requena's tool (2003) that evaluates social relationships and contacts between colleagues.
In the second step we evaluated the 21 selected items based on whether: (i) they were in line with our definition of WSC, and (ii) they could be applied to all organizations.  Kouvonen et al. (2007) 8-item, unidimensional scale assessing mutual trust, reciprocity, solidarity, collective action and transparent decision-making processes, taping (to some extent) bonding, bridging and linking WSC (e.g.,"People in the work unit cooperate in order to help develop and apply new ideas" and "Our supervisor shows concern for our rights as an employee") Pejtersen et al. (2010) 11-item, three-dimensional scale assessing (i) trust among employees (3 items; e.g., "Employees in general trust each other"), (ii) trust of management (4 items; e.g., "The management trusts the employees to do their work well"), and (iii) workplace justice (4 items; e.g., "The work is distributed fairly") Eguchiet al. (2017) 6-item, unidimensional scale assessing trust (e.g., "In our workplace, we trust each other"), reciprocity (e.g., "In our workplace, there is an atmosphere of helping each other") and network aspects (e.g., "People feel understood and accepted by each other") of bonding WSC Ommen et al. (2009) 6-item unidimensional scale assessing social support, common values and trust within an organization (e.g., "At our workplace we trust each other" and "Agreement and consent dominate in our workplace")  21-item, four-dimensional scale assessing WSC (i) within teams (6 items; e.g., "In my team, we help colleagues who have too much to do") (bonding WSC), (ii) between teams (6 items; e.g., "My team and Team X acknowledge each other's contribution to solve the work task") (bridging WSC), (iii) in relation to the immediate management (6 items; e.g., "Our immediate manager takes our needs and views into consideration when he/she makes decisions") (linking WSC), and (iv) in relation to the workplace as a whole (3 items; e.g., "There is a common understanding between the management and employees about how we complete our tasks") (linking WSC) Based on these criteria, 11 items were selected and adapted. Namely, the terms "employees" or "individuals" were replaced with "colleagues", in some items a clear reference to colleagues was added, questions were transformed to affirmative statements, and items of bridging WSC were formulated to refer to the immediate supervisor or management.
In the third step, we generated 24 new items to capture aspects of our definition that were not assessed by the selected items. To measure reciprocity of bonding WSC, we distinguished between instrumental and emotional support for work and non-work-related problems. Also, to measure trust and reciprocity of bridging WSC, we created bilateral items (e.g., from supervisor/management to employee and vice versa). Moreover, to evaluate the network dimension of bridging WSC, we developed items to assess opportunities that the organization provides to employees for expanding their network outside of the organization.
In the fourth step, all authors evaluated the items independently and proposed modifications to enhance clarity and face validity. The content validity of the final items was evaluated by all authors based on the definitional correspondence and definitional distinctiveness criteria in line with Colquitt et al. (2019). The final version included 37 items.

Phase 3: Psychometric Evaluation of the WoSCi
In Phase 3, we tested the psychometric properties of the new scale, using separate samples according to best practice recommendations (Worthington & Whittaker, 2006). First, we explored the initial structure of WoSCi. Then, we confirmed the final factor structure of the scale by means of multilevel confirmatory factor analysis. Next, we tested the internal consistency of the new scales. Finally, we tested the convergent, criterion-related and incremental validity of WoSCi, and we conducted usefulness analysis.

Exploring the Initial Structure of the WoSCi
First, we performed exploratory factor analyses (EFA), to test the initial Structure of WoSCi. Namely, with these analyses we were interested in identifying the items that better capture WSC.

Participants and Procedure
We collected data via an online questionnaire, by sending email invitations to all employees of 14 universities in Greece (N = 4245). We informed participants about the study aims and procedure and reassured them that participation was voluntary and anonymous, and that data were confidential. The final sample (Sample 1) comprised 376 employees (response rate 8.8%). Low response rates are common on web-surveys and do not necessary imply differences between respondents and non-responders (Sappleton & Lourenço, 2016). Almost half of the participants were women (50.9%), with an average age of 47.91 years (SD = 8.24). Fifty percent were academics and 15.7% were administrative employees, while most (90%) worked full-time.

Measures
Workplace Social Capital was measured with the 37-item scale that was distributed in Greek. Items were scored on a 5-point scale, ranging from (1) "fully disagree" to (5) "fully agree".

Strategy of analysis
We performed EFA using Principal Axis Factoring with Promax rotation that is appropriate when new scales are developed and when factors are not independent.

Results
We assessed the adequacy of the model with Kaiser-Meyer-Olkin (KMO) and Bartlett's Test of Sphericity (ΚΜΟ = 0.95, χ 2 = 11,398.14, p < 0.001). The analysis resulted in five factors that explained 67.74% of the total variance. We excluded the fifth factor since it consisted of one item. Moreover, three items had loadings < 0.40 and two items loaded on two factors with loadings > 0.40, so these were also excluded.
Next, we conducted an EFA with the remaining 31 items. The EFA based on the 31-item solution resulted in the following four factors: all items measuring trust and reciprocity (i.e., cognitive WSC) at the bonding level loaded on the first factor (loadings ranged from 0.59 to 0.88, explained variance = 44.31%), all items measuring network (i.e., structural WSC) at the bonding level loaded on the second factor (loadings from 0.55 to 0.72, explained variance = 2.57%), all items measuring trust and reciprocity (i.e., cognitive WSC) at the bridging level loaded on the third factor (loadings from 0.53 to 0.94, explained variance = 11.06%), and all items measuring network (i.e., structural WSC) at the bridging level loaded on the fourth factor (loadings from 0.71 to 0.94, explained variance = 7.03%). These findings support a four-factor structure that distinguishes between structural and cognitive, as well as bonding and bridging WSC, but does not distinguish between the two dimensions (i.e., trust and reciprocity) of cognitive WSC as hypothesized (see Fig. 1).
To further reduce the length of the scale in order to address the issue of assessment burden, we excluded seven more items based on both content validity and statistical evidence (i.e., factor loadings, inter-correlations). Namely, we excluded four items due to high conceptual overlap with items with higher or similar factor loadings. Also, we excluded the only remaining reverse-worded item (see, Van Sonderen et al., 2013). Finally, we excluded two items that evaluated reciprocity less directly than the remaining items. Table 4 presents the EFA results of the final, 24-item version of the WoSCi. The EFA again resulted in four factors distinguishing between bonding cognitive WSC (merging trust and reciprocity at the bonding level), bonding structural, bridging cognitive (merging trust and reciprocity at the bridging level), and bridging structural WSC.

Confirming the Structure of the WoSCi
We investigated the factor structure of the final version of the WoSCi by performing confirmatory factor analyses (CFAs) and by accounting for the multilevel nature of the construct and the potential interdependency in the assessments of employees belonging to the same organization. CFAs are relevant because they allow testing whether the scale captures  Kouvonen et al. (2007); items 1 and 13 were adapted from COPSOQ II (Pejtersen et al., 2010); item 10 was adapted from Requena (2003). ΚΜΟ = .95; χ 2 = 7508.11, p < .001; Total variance explained = 67.47%; Variance explained for Factor 1 = 12.37%; Factor the construct in line with theory. Further, accounting for the multilevel nature of the construct is relevant because WSC, as an ecological resource, may capture both individual, as well as shared perceptions that may be aggregated at the organizational level of analysis. Given that the four-factor structure of the WoSCi that resulted from the EFAs was not aligned with the proposed theoretical framework of the construct (see Fig. 1), another aim was to test whether the hypothesized factor structure explains the data better than the factor structure that resulted from the EFA.

Participants and Procedure
Three independent samples were merged for the analyses. The first (N = 216; Sample 2) consisted of employees working in 62 mental health-care organizations (response rate = 78.5%). Most participants were women (85.2%). Participants' mean age was 44.41 (SD = 6.53) years, while the majority (73.1%) held a university degree. Forty percent were psychologists, 17.6% social workers and 16.3% administrative staff, while their average job tenure was 14.41 (SD = 5.08) years. The second sample (N = 331; Sample 3) concerned a heterogeneous group of employees nested in 53 organizations (response rate = 83.8%). Employees were approached through snowball sampling. Most participants were women (70.4%). Their mean age was 42.98 years (SD = 9.30) years and 37.5% held a university degree. Most (30.8%) of them were teachers in primary and secondary schools, 19.9% were administrative staff and 8.5% were nurses. Participants' average job tenure was 10.88 (SD = 9.15) years.
The third sample consisted of 186 employees nested in 43 organizations mainly from the education and the service sector (Sample 4). Most participants were women (64.5%). Their mean age was 37.30 (SD = 11.63) years and the majority were university graduates (68.90%). Participants' average tenure in the current position was 9.88 years (SD = 9.44). In total, the merged sample included 733 employees nested in158 organizations (73.8% women; average age: 41.92 years SD = 9.49; average organizational tenure: years 11.67 SD = 8.43).

Measures
WSC was assessed with the 24-item WoSCi (see Table 4).

Strategy of Analysis
To account for the hierarchical nature of the data [i.e., employees (level 1) nested in work units (level 2)], we performed MLCFA. MLCFA allows estimating model parameters while accounting for the autocorrelation induced by the levels of the clustering variable (Bryk & Raudenbush, 1992). The main advantage is that standard errors of fixed effects are adjusted to account for the cluster sampling effect thus, increasing the accuracy of estimation (Julian, 2001). We compared three models: (1) a one-factor model, where all 24 items loaded on an overall WSC latent factor (Model 1); (2) a four-factor model as resulted by the EFA analyses; and (3) an hierarchical model, with two higher-order factors (WSC bonding and bridging) that were allowed to covary freely, each of which consisted of a cognitive (which in turn was composed of trust and reciprocity lower-order factors) and a structural (i.e., network) WSC factor (Model 3). Trust, reciprocity and network factors were manifested by the respective items.
MLCFAs were performed with Mplus Version 8.4 (Muthén & Muthén, 2017), using maximum likelihood with robustness to non-normality and non-independence of observations (MLR) as method of model estimation. The MLR chi-square test statistic is asymptotically equivalent to the Yuan-Bentler T2 test statistic. Model fit was evaluated using the χ 2 goodness of fit index, the Comparative Fit Index (CFI), the Tucker-Lewis Index (TLI), the Root Mean Square Error of Approximation (RMSEA) and the Standardized Root Mean Residual (SRMR). For CFI and TLI values close or greater to 0.95 show good data fit (Hu & Bentler, 1999). For RMSEA, values lower than 0.05 indicate good fit and values up to 0.08 a reasonable fit, and for SRMS values less than 0.08 are acceptable. We also used the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC) for model comparisons.

Results
The results of the MLCFAs are presented in Table 5. The one-factor model (Model 1) did not show an adequate fit to the data. Models 2 and 3 had acceptable fit, although Model 3 showed a significantly better fit compared to Model 2 [Δχ 2 (3) = 105.69, p < 0.001]. These results suggest that the theoretically proposed, hierarchical structure ( Fig. 1) better depicts the WSC construct than the four-factor structure resulted from the EFA. Importantly, the hypothesized higher-order factor structure of WSC was found to hold at the individual level of analysis after accounting for the nested structure of the data and the effect of the clustering variable (i.e., organization membership).
Since analyses supported the proposed structure of WSC, while accounting for the multilevel nature of the construct, we also investigated whether individual level data could be aggregated at the work-unit level of analysis. Thus, we estimated inter-rater agreement (IRA) and inter-rater reliability (IRR) for the total scale and for each separate forms and dimension of the WoSCi. Within-unit IRA was tested with the r wg index and the average deviation (AD) index, while IRR (i.e., between-group variability) was tested with the intra class correlation coefficient (ICC). Values > 0.70 for r wg , < 0.80 for AD and at least 0.12 for ICC justify aggregation (LeBreton & Senter, 2008). Results fully supported aggregation at the work-unit level of analysis (WoSCi: r wg = 0.97; AD = 0.49; bonding WSC: r wg = 0.95; AD = 0.48; bridging WSC: r wg = 0.96; AD = 0.50; WoSCi sub-dimensions: 0.80 < r wg < 0.9 5;0.44 < AD < 0.52). ICCs were acceptable for all items (0.21 < ICCs < 0.38).

Reliability and Validity of the WoSCi
Finally, we tested the reliability and the validity of the WoSCi.

Reliability
To estimate the internal consistency of WoSCi, we estimated the Cronbach' s alpha and the Omega Index.

Convergent Validity
Convergent validity was tested by exploring the associations between WoSCi and other commonly used scales measuring WSC namely, the scales of Pejtersen et al. (2010) and Kouvonen et al. (2007). Hence: Hypothesis 1 Other WSC scales will correlate highly and positively with the WoSCi.
Also, we tested the relationship of WoSCi with other, theoretically similar, yet distinct constructs. Although some scholars perceive justice as a dimension of WSC (Pejtersen et al., 2010), most studies showed that justice is a related, yet distinct construct (Eguchi et al., 2017;Kouvonen et al., 2007). Therefore, we expected: Hypothesis 2 WSC will correlate positively with organizational justice.
Next, we assessed the relationships of WSC as measured with the WoSCi with different leadership styles, since leaders commonly determine organizational values. Transformational leaders can enhance key features of WSC such as trust and cooperation (Chen et al., 2016), and may motivate employees to build external networks (Brion et al., 2012). In contrast, abusive supervisors, who display hostile verbal and non-verbal behaviors toward their subordinates (Tepper, 2000) are likely to create an unsupportive environment (Shoss et al., 2013) and negative reciprocity beliefs. Hence: Hypothesis 3 WSC will correlate positively with transformational leadership and negatively with abusive supervision.
Since WSC is conceptualized as a workplace resource, we expect, in the context of job demands-resources (JD-R) theory (Bakker & Demerouti, 2017), that it correlates positively with other relevant job resources (i.e., participative decision making, performance feedback, job autonomy, and colleagues' social support). Participative decision making may strengthen and improve the quality of social relationships in the workplace, especially between supervisors and subordinates (Somech, 2010). Performance feedback implies open and direct communication between different parts (Krasman, 2012), which may promote or be promoted by aspects like trust and positive interactions at work. Job autonomy was also found to associate positively with WSC (Kouvonen et al., 2007). An organization high in WSC may allocate more autonomy to employees, due to the experienced trust. Similarly, by feeling responsible for their jobs, employees with greater job autonomy are more likely to create a mutual trustful and cooperative work involvement (Wang & Cheng, 2010). Finally, social support is closely related to the reciprocity dimension of WSC. Meanwhile, trust is an important condition that facilitates the development of supportive relationships, while network dimension reflects the quality of social ties that may guarantee social support. Therefore: Hypothesis 4 WSC will correlate positively (a) with participative decision making, (b) performance feedback, (c) job autonomy and (d) colleagues' social support.

Criterion-Related Validity
We tested criterion-related validity by exploring the relationships of WSC with work engagement, burnout, and job performance. According to JD-R theory (Bakker & Demerouti, 2017), job resources are the main drivers of employee motivation since they facilitate goal attainment while promoting personal growth and development. WSC may help employees be functional in achieving work goals making them more vigorous, dedicated and absorbed (i.e., engaged) in their work . Similarly, employees working in an organization high in WSC, are more likely to feel a sense of obligation that may translate in increased in-role job performance (Eisenberger et al., 2001), and to invest in positive citizenship behaviors, such as extra-role performance (Sparrowe et al., 2001). In line with JD-R theory, job resources are also the main drivers of the disengagement component of burnout since high levels of resources protect employees from becoming cynical about their work. Also, job resources help employees deal with high job demands thus, mitigating their unfavorable impact of the exhaustion component of burnout. In this context, we argue that WSC will relate negatively with burnout (Kowalski et al., 2010). Thus: Hypothesis 5 WSC will relate positively with work engagement (a) and job performance (b), and negatively with burnout (c).

Incremental Validity
We tested the incremental validity of the WoSCi in explaining work engagement, burnout and job performance over and above other constructs that capture capital namely, personal SC (Chen et al., 2009) and psychological capital (PsyCap; Luthans et al., 2007). The common ground between the different forms of capital is that they create value (Luthans et al., 2007). However, they contribute towards that end in different ways. While in the case of WSC employees evaluate whether trust, reciprocity and social networking characterize interactions within their organization, in the case of personal SC actors evaluate the amount to which these aspects characterize their own personal interactions (Chen et al., 2009). PsyCap, just like personal SC, is a personal resource that consists of high levels of self-efficacy, hope, resilience and optimism (Luthans et al., 2007). However, although personal SC or WSC refers to trust, reciprocity and social interactions that may contribute to problem solving through answering questions like "to whom can I turn for help", PsyCap refers to personal characteristics that promote problem-solving through personal development (Luthans et al., 2007). Hence: Hypothesis 6 WSC explains variance in work engagement, burnout, and job performance over and above personal SC and PsyCap.

Participants
We used all four samples (see Table 6).

Measures
Items were rated on a five-point scale ranging from (1) "fully disagree" to (5) "fully agree", except if stated otherwise.
WSC was measured with the WoSCi (Table 4) and the scales of Kouvonen et al. (2007) and Pejtersen et al. (2010). Example items of the latter scales are presented in Table 3.
Justice. Perceived justice was measured with three items from the Ambrose and Schminke (2009) scale (e.g., "Overall, I'm treated fairly by my organization"). Distributive justice was measured with the 5-item scale of Moorman (1991; e.g., "How fairly you are rewarded by the organization you work for the amount of effort you put forth?"). Procedural justice was measured with five questions from the scale of McFarlin and Sweeney (1992; e.g., "To which extent the procedures that are followed from your organization regarding performance evaluation are fair?"). Distributive and procedural justice items were rated on a scale ranging from (1) "not at all" to (5) "to a very large extent".
Leadership. Transformational leadership was assessed with the seven items used by Tims et al., (2011;e.g., "My supervisor stimulates us to think of solutions for problems that we face in work"). Abusive supervision was measured with Tepper' s (2000) 15-item scale (e.g., "My supervisor ridicules me"), with answers provided on a scale ranging from (1) "I cannot remember him/her using this behavior with me" to (5) "he/she uses this behavior very often with me". Table 6 Reliability of scales and correlations between the study variables Sample 1 (Study 2, N = 376); Sample 2 (Study 3, N = 216); Sample 3 (Study 3, N = 331); Sample 4 (Study 3, N = 186) **p < 0.01 level The total WoSCi was positively correlated with the bonding (r = .84, p < .01) and bridging (r = .92, p < .01) sub-scales, while the bonding and bridging sub-scales were also positively correlated (r = .53, p < .01) in the total sample of Study 3 Job resources. Participative decision making was measured with Probst's (2005) 6-item scale (e.g., "Supervisors encourage workers to set their own work-related goals"). Performance feedback was measured with three items (e.g., "My work provides me with direct feedback on how well I am doing my work") used by Bakker et al. (2003). Job autonomy was assessed with three items such as "I can decide myself how I execute my work" (Bakker et al., 2004). Colleague support was measured with three items such as: "I can ask my colleagues for help, if necessary" (Bakker et al., 2004). Items of the three last scales were rated on a scale ranging from (1) "never" to (5) "always".
Work engagement was measured with the 9-item version of the Utrecht Work Engagement Scale (Schaufeli et al., 2006). Responses are given on a scale ranging from (0) "never" to (6) "always".
Burnout was assessed with the Oldenburg Burnout Inventory ) that consists of 16 items, eight of which measure exhaustion (e.g., "After my work, I regularly feel worn out and weary") and eight disengagement (e.g., "I frequently talk about my work in a negative way"). Responses were given on a scale ranging from (1) "strongly agree" to (4) "strongly disagree".
Job performance. In-role (e.g., "I achieve the objectives of my job") and extra-role (e.g., "I help colleagues when returning at work after a period of absence") performance were measured with six items from the scale of Goodman and Svyantek (1999). Items were answered on a scale from (1) "never" to (6) "always".
Personal social capital was measured with Chen et al.'s (2009) scale. Bonding SC was assessed with five items evaluating individuals' network size, frequency of social contacts, trust, reciprocity and social support and resources possessed from network members. Bridging SC was assessed with five items evaluating the extent to which someone is embedded in different types of organizations. One item was added, assessing trust regarding community groups and organizations. For a detailed description, refer to Chen et al. (2009).
Psychological capital was measured with the 12-item version of Psychological Capital Questionnaire (Luthans et al., 2007) that assesses: (a) self-efficacy (three items; e.g., "I feel confident presenting information to a group of colleagues"); (b) hope (four items; e.g., "If I should find myself in a jam at work, I could think of many ways to get out of it"); (c) resilience (three items; e.g., "I usually take stressful thing at work in stride") and (d) optimism (two items; e.g., "I always look on the bright side of things regarding my job"). Items were rated on a scale from (1) "strongly disagree" to (6) "strongly agree". The PCQ-12 was used with permission of Mind Garden. [www. mindg arden. com].

Strategy of Analysis
To estimate the internal consistency of the WoSCi, we opted for the composite reliability or omega index (McDonald, 1999). However, we also report alpha values to allow comparisons with other WSC scales. To test convergent validity, we estimated correlations at the individual level of analysis between the WoSCi and the investigated constructs, following the recommendations of Cohen (2013; i.e., r = 0.10 weak; r = 0.30 moderate; r = 0.50 high). To test for criterion-related and incremental validity we conducted regression analyses with work engagement, burnout and job performance as outcome variables. We entered the WoSCi in the first step of the equation and added SC or/and PsyCap in the second step. Also, we assessed the reversed effects, where SC or/and PsyCap were entered first, followed by the WoSCi.

Convergent Validity
As shown in Table 6, WoSCi correlated positive and highly with the WSC scales of Kouvonen et al. (2007) and Pejtersen et al. (2010), supporting Hypothesis 1. The WoSCi also correlated positively with overall, distributive and procedural justice supporting Hypothesis 2. The reported correlations were moderate in most cases suggesting that justice and WSC are related yet distinct constructs. Further, the WoSCi related positively with transformational leadership and negatively with abusive supervision, supporting Hypothesis 3. In both cases the correlations were higher for bridging WSC, which refers more directly to supervision. Finally, the WoSCi correlated positively with all other job resources supporting Hypothesis 4. Importantly, all these associations were not as high, as to imply overlapping constructs. Correlations were also calculated at the organizationallevel of analysis, providing similar results. These correlations are available from the first author upon request.

Criterion-Related and Incremental Validity
The results of the hierarchical multiple regression analyses (N = 547) showed that the WoSCi related positively and significantly with work engagement (β = 0.44; p < 0.001), inrole (β = 0.23; p < 0.001) and extra-role performance (β = 0.27; p < 0.001) and negatively with burnout (β = − 0.41; p < 0.001), supporting Hypothesis 5. Results regarding incremental validity showed that WoSCi explained significant additional variance in almost all tests. The statistically significant changes in multiple correlations (ΔR 2 ) when WoSCi entered after individual SC ranged from 0.04 to 0.15 (p < 0.001) in work engagement, burnout, in-role and extra-role performance, and when WoSCi entered after PsyCap or after both individual SC and PsyCap ranged from 0.01 to 0.06 (p < 0.001) in for work engagement, burnout and extra-role performance (but not in-role performance). These results provide support for Hypothesis 6.
We also conducted usefulness analysis (Darlington, 1990) to test the added value of WoSCi as a composite factor in explaining work engagement, burnout, and job performance, beyond each of its dimensions. Results indicated that overall WoSCi increased the multiple correlation value beyond its individual components in all cases, where changes in R 2 ranged from 0.01 to 0.16 and were all statistically significant.

Discussion
The aim of this paper was two-fold: to propose an integrated definition of WSC and to develop and validate a scale for its measurement. These aims were put forward across a study which included three phases. Motivated by the lack of consensus in what WSC is and how it may be measured (Oksanen et al., 2013), in Phase 1, we performed a literature review to detect the core and unique elements of WSC that allow distinguishing it from other related constructs. On this basis, we defined WSC as an ecological resource that concerns employees' perceptions regarding trust, reciprocity (cognitive WSC), and network interactions (structural WSC) that exist both among peers (bonding WSC) and among individuals across different hierarchical levels or organizations (bridging WSC). In Phase 2, based on this definition, we developed the WoSCi. In Phase 3, we tested the psychometric properties of the new scale. Results validated the WoSCi' s proposed structure by accounting for the multilevel nature of the construct. Results revealed that the WoSCi is a reliable and valid scale and may explain work-related well-being and performance over and above other forms of capital. In what follows, we discuss in detail the theoretical, empirical and practical implications of the study findings.

Theoretical and Empirical Implications
Our study contributes to the development of the WSC construct by synthesizing a theorydriven definition. Although studies on WSC are constantly increasing, there is no consensus regarding its definition (Read, 2014). To address this issue, we applied a theoretically driven approach, and defined WSC based on fundamental distinctions regarding its forms and core facets. Thus, the proposed definition of WSC as an ecological workplace resource is theoretically justified and valid since it incorporates all its central components, while it also dictates how these inter-relate with each other forming the concept. In this way we expand the nomological network of WSC by clarifying what WSC is, how it is constructed and how it relates with similar, yet different constructs.
Our theoretical analysis suggested that WSC is a higher-order construct that evolves at the bonding and bridging levels each of which consist of a cognitive (which in turn is composed of trust and reciprocity lower-order factors) and a structural (i.e., network) component. Although, the results of the EFAs suggested that trust and reciprocity were merged in one factor both at the bonding and bridging levels, the MLCFAs supported our theoretical model by showing that trust and reciprocity are distinct underlying components of cognitive WSC. This is important when considering that most existing approaches (Kouvonen et al., 2007;Ommen et al., 2009) do not clearly distinguish between trust and reciprocity or do not evaluate them at both bonding and bridging levels. Trust and reciprocity are closely related constructs. Trust refers to expectations of honest behavior and is linked to the belief that others will react positively to an initiative, or at least they will not undermine it. Thus, it makes the various parties during a social interaction reliable (Fukuyama, 1997). Reciprocity is related to support exchange and refers to the provision of help, with the expectation that at some point it will be reciprocated (Harpham et al., 2002). Despite their similarities, trust and reciprocity differ in that reciprocity is a broader concept, which integrates expectations regarding social action and includes the criterion of practical mutual assistance (Harpham et al., 2002). An advantage of our approach is that it manages to theoretically and empirically support the unique contributions of trust and reciprocity in the WSC construct.
Implications regarding measurement are also manifold. We argued and showed that the WoSCi fully captures WSC and not just a part of it since it measures both the cognitive and the network facet of WSC, while incorporating the bonding/bridging distinction. This is relevant because it supports empirically that the cognitive and structural components of WSC may exist at different directions (i.e., inward/outward). As such, the WoSCi overcomes limitations of existing measures that do not include reciprocity (Pejtersen et al., 2010), do not distinguish between reciprocity and trust (e.g., Ommen et al., 2009), or do not evaluate these dimensions at both bonding and bridging levels (Eguchi et al, 2017;Kouvonen et al., 2007). Moreover, the WoSCi may be used to assess WSC in every work environment. Despite the complexity of its theoretical structure that often results in nonuser-friendly instruments (e.g., , the WoSCi measures WSC in a straightforward way in all organizational contexts irrespective of their size or structure. Importantly, the proposed structure of WSC, as measured with the WoSCi, was supported when accounting for the nested structure of the data, which further supports the stability of the construct, and its potential, multilevel nature. The empirical and practical value of the WoSCi is further boosted by the findings supporting that is a reliable and valid tool. Correlational analyses supported the convergent validity of the WoSCi since it was found to relate substantially with other scales measuring the same construct as well as scales measuring related constructs. Although WoSCi correlated positively and highly with justice and leadership, the associations were not as high as to imply overlapping constructs. Especially concerning justice, results did not suggest that it is a core element of WSC, as implied by Petersen et al. (2010). Also, the positive correlations of WSC with other job resources, as well as the criterion-related validity results showing that it relates positively to work engagement and performance, and negatively to burnout, indicate that WoSCi can be perceived as a job resource (Bakker & Demerouti, 2017).
Last but not least, results provided evidence regarding WSC' s incremental validity in explaining significant outcomes, over and above other forms of capital. Namely, we showed that WSC explains variance in work engagement, burnout and extra-role performance beyond personal SC (Chen et al., 2009) and PsyCap (Luthans et al., 2007). These findings suggest that workplace capital matters and may complement individual forms of capital. However, the incremental validity of WSC was not supported for in-role job performance, indicating that PsyCap, alone or together with individual SC, are more relevant in explaining this facet of performance. This may be attributed to the nature of WSC that is more closely related to employees' attitudes that are driven by altruism (i.e., extra-role performance), since it reflects the team spirit (i.e., trust, reciprocity) within organizations. In contrast, PsyCap reflects individual qualities that are necessary for responding to setbacks and for invest the necessary effort to achieve formal duties requirements (Luthans et al., 2007).

Practical Implications
Our results have important implications for organizational practice. Considering the incremental validity results, organizations may implement interventions aiming at enhancing WSC. Such interventions should aim at promoting trust and reciprocity within the organization both among employees and across levels of hierarchy. Relevant action plans, that could be put in practice through workshops and other training methods, may include tasks targeting to communication, social cohesion and cooperation improvement, energetic involvement of employees in decision making process and development of shared understanding regarding work tasks . Also, it is important for organizations to promote networking opportunities within organization and facilitate processes that allow developing partnerships with other organizations in order to expand the network of an organization and the opportunities for employees' professional and social development.

Study Limitations and Avenues for Future Research
Our study has some limitations. First, we did not examine the test-retest reliability of the WoSCi so we do not have evidence for its stability over time. Second, criterion-related validity was also assessed using cross-sectional data. Future research should make use of longitudinal data to further test the validity of the scale. Third, all studies have been conducted in Greece, so we do not have evidence regarding the reliability and validity of the WoSCi in different cultures. Future cross-cultural studies would allow testing the factorial invariance of the scale across different contexts. Forth, we used convenience samples, which are characterized by low generalisability. However, the use of heterogeneous samples somewhat counteracts this limitation.
To conclude, in this study we defined WSC as an ecological, job resource and we developed a reliable and valid instrument to measure this construct. WSC was found to be relevant in explaining employee well-being and job performance over and above other forms of capital. Our results highlight the theoretical, empirical, and practical relevance of WSC as a type of resource that may promote flourishing in organizations.
"those expectations for action within a collectivity that affect the economic goals and goal-seeking behavior of its members, even if these expectations are not oriented toward the economic sphere" (Portes & Sensebrenner, 1993;p. 1323) "the existence of a certain set of informal values or norms shared among members of a group that permits cooperation among them" (Fukuyama, 1997;p. 378) "norms and networks that enable people to act collectively" (Woolcock & Narayan, 2000;p. 226) "includes the institutions, the relationships, the attitude and values that govern interactions among people and contribute to economic and social development….It includes the shared values and rules for social conduct expressed in personal relationships, trust, and a common sense of civic responsibility, that makes society more than a collection of individuals" (World Bank, 1998;p. 5) "the set of elements of the social structure that affects relations among people and are inputs or arguments of the production and/or utility function" (Schiff, 1992;p.160) "is the shared knowledge, understandings norms, rules and expectations about patterns of interactions that groups of individuals bring to a recurrent activity" (Ostrom, 2000;p. 176) "the web of cooperative relationships between citizens that facilitate resolution of collective action problems" (Brehm & Rahn, 1997; p. 999) '' both the different network structures that facilitate (or impede) access to social resources and the nature of social resources embedded in the network '' (Seibert et al., 2001; p.221 "is defined by its function. It is not a single entity, but a variety of different entities having two characteristics in common: They all consist of some aspect of social structure, and they facilitate certain actions of individuals who are within the structure" (Coleman, 1988;p. 98) "networks together with shared norms, values and understandings that facilitate cooperation within or among groups" (Organization for Economic Cooperation and Development-OECD, 2001; p. 41) "the web of social relationships that influences individual behavior and thereby affects economic growth" (Pennar, 1997;p. 154) "the sum of the actual and potential resources embedded within, available through, and derived from the network of relationships possessed by an individual or social unit. Social capital thus comprises both the network and the assets that may be mobilized through that network" (Nahapiet & Ghoshal, 1998;p. 243) ''is the goodwill available to individuals or groups. Its source lies in the structure and content of the actor's social relations. Its effects flow from the information, influence, and solidarity it makes available to the actor'' (Adler & Known 2002; p. 23) ''resources available to individuals and groups through membership in social networks'' (Vilalonga-Olives & Kawachi, 2015; p. 47) "a culture of trust and tolerance, in which extensive networks of voluntary associations emerge" (Inglehart, 1997;p. 188) Author Contributions All authors contributed to the study conception and design. Material preparation and data collection were performed by AT and DX. Analyses were performed by AT and IT. The first draft of the manuscript was written by AT and all authors commented on previous version of the manuscript. The supervision of the study was made by DX, ED and KK. All authors read and approved the final manuscript.
Funding Open access funding provided by HEAL-Link Greece. No Funds, Grants, or other support was received.

Data Availability
The data that support the findings of the study are available from the corresponding author [Andreas Tsounis], upon reasonable request.

Conflict of interest
The authors have no conflicts of interest to declare that are relevant to the content of this article.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.