Towards a better understanding of volunteer engagement: self-determined motivations, self-expression needs and co-creation outcomes

Purpose – Non-profit organizations (NPO) contribute significantly to the welfare of citizens and communities. EngagementinvolunteeringiscrucialforsustainingvolunteermotivationandfortheeffectiveandefficientfunctioningofNPO,withsignificantimplicationsforsocietyatlarge.Yet,literatureonvolunteerengagement(VE)islimitedtodate.Groundedonservice-dominantlogic,self-congruitytheoryandself-determinationtheory,thisstudyaimstounderstand whatmotivatesVEandhowitmayevolveintoaco-creationprocessvaluabletoNPOanditsstakeholders. Design/methodology/approach – Based on survey data collected from 450 volunteers, working with a diverse set of NPO, a comprehensive model of drivers and outcomes of VE was empirically tested using PLS-SEM, considering the mediating role of volunteers ’ congruence with the core values of the NPO. Findings – The impact of volunteers ’ perceived autonomy, competence and relatedness on VE and its subsequent role in volunteers ’ loyalty and extra-role engagement behaviors (i.e. co-development, influencing and mobilizing behaviors) were validated. Moreover, the study validates value congruence as an internalizing mediating mechanism in the engagement process, a role that has been implied but not empirically tested. Originality/value – The study contributes to the engagement and volunteering literature, which despite an unprecedented parallel have developed almost independently, with limited reference to one another. As the nomologicalnetworkofVEisstillunderexplored,thestudyextendstheengagementliteraturetothevolunteering sector, validating the key (but underexplored) role of self-determination needs and value congruence in driving VE and value co-creation behaviors. The study further adds to engagement research while addressing other actors ’ engagementbeyond the customer – branddyad. Whileadopting a seldom exploredmarketing perspective of VE, this study provides NPO valuable insights on how to manage and engage volunteers.


Introduction
Volunteering has become the backbone of modern society (Conduit et al., 2019).Defined as an act of free will that results in benefits to others (UN, 2000), usually developed within non-profit organizations (NPO), it contributes significantly to the welfare of citizens and communities (Mekonen and Adarkwah, 2022).The volunteer industry is also an essential part of many economies, contributing to almost 2.5% of global GDP (UN, 2015).For example, the economic value of volunteering has been estimated at AUD$29bn in Australia (Volunteering Australia, 2015), whereas in the US non-profit services represent 5.4% of GDP (Traeger and Alfes, 2019).According to the National Council for Voluntary Organizations, the voluntary sector contributed GBP£20bn to the UK economy in 2020, representing around 1% of GDP (NCVO, 2021), amounting in many European Union countries to more than 2% of GDP (EESC, 2021).The economic weight of the non-profit sector has been continuously increasing (Matos and Fernandes, 2021), with NPO becoming the main actors in critical areas such as education, health or social services.
While combining an entrepreneurial spirit with a concern for public welfare, NPO operate in a competitive environment (Curran et al., 2016), where retaining engaged volunteers is crucial to maintain their regular activities (Malinen and Harju, 2017).The growing demand and competition for this valuable resource requires organizations to better understand key drivers that determine volunteers' engagement and ongoing retention (Conduit et al., 2019).Engagement in volunteering is critical as it relates to how volunteers perform their roles (O'Brien et al., 2020) and has significant implications for NPO, volunteers, beneficiaries and society at large (Traeger and Alfes, 2019).Yet, despite the importance of retaining motivated volunteers, literature on volunteer engagement (VE) is limited to date (Yoo et al., 2022).Moreover, the scant existing research has mostly focused on the perspective of the NPO, while little work has been undertaken to consider VE from the volunteers' point of view (Conduit et al., 2019).
Conceptualized as a positive motivational construct, resulting in higher involvement, dedication and vigor in task performance (Vecina et al., 2012), VE is still a relatively new concept in volunteering research (Traeger and Alfes, 2019).Yet, in other fields such as service management, engagement has been widely explored, with the literature on customer engagement (CE) rapidly advancing in the last decades (Hollebeek et al., 2022).Defined as a "psychological state that occurs by virtue of interactive, co-creative customer experiences with a focal agent/object (e.g. a brand) in focal service relationships" (Brodie et al., 2011, p. 9), the concept originally focused on CE with brands.Yet, a recent sub-stream recognizes the importance of extending CE's scope to a broader range of focal actors beyond the customerbrand dyad (Hollebeek et al., 2022).Actor engagement (AE) is a dynamic, iterative process, where actors invest resources in their interactions with other actors within a service system (Brodie et al., 2019).Such a definition means that an actor can be any subject, including a citizen (Jaakkola and Alexander, 2014), a student (Sim and Plewa, 2017) or a volunteer (Brodie et al., 2019).Hence, this emerging sub-stream acknowledges all these actors as resourceintegrating agents that engage in various contexts.
Engagement occurs within a dynamic, iterative process that co-creates value (Brodie et al., 2013).As such, studying engagement is particularly relevant due to the potential behaviors resulting from actor-to-actor interactions, namely the co-creation of value that can emerge.Engagement behaviors are actor's voluntary contributions, not elementary to exchange, that occur in interactions with a focal object and/or other actors (Alexander et al., 2018).Engagement can thus lead to extra-role behaviors that an actor is willing to perform beyond the call of duty (Jaakkola and Alexander, 2014), leading to an intrinsic connection between engagement and co-creation (Fernandes and Remelhe, 2016).This may be particularly true in a volunteering context, where volunteers actively commit their resources to the benefit of a third party (i.e. the beneficiaries), but also co-create value for themselves and the NPO (Conduit et al., 2019).Volunteering may thus extend beyond formally expected tasks such as interacting with colleagues and following rules, to include spreading positive word-of-mouth about the NPO to other potential volunteers or sharing JSTP 33,7 service improvement suggestions.These extra-role, discretionary behaviors are not elementary to exchange nor formally required to deliver aid or meet community needs, but provide significant benefits overall (Groth, 2005).Yet, surprisingly, most VE studies have not fully examined volunteers' extra-role engagement behaviors (Yoo et al., 2022).
Following these literature gaps and addressing recent calls for further research on value co-creation and engagement in a non-profit, social services context (Donthu et al., 2022;Zainuddin and Gordon, 2020;O'Brien et al., 2020), this study aims to understand what motivates VE and how it may evolve into a co-creation process valuable to the NPO and its stakeholders.Grounded on service-dominant logic (SDL) (Vargo and Lusch, 2004), selfcongruity theory (SGT) (Sirgy, 1985) and self-determination theory (SDT) (Deci and Ryan, 2000), a model of drivers and outcomes of VE was empirically tested.Based on survey data collected from 450 volunteers working with a diverse set of NPO, the impact of volunteers' perceived autonomy, competence, relatedness and value congruence on VE and its subsequent role for volunteers' retention and extra-role behaviors were validated.
The study contributes to the engagement and volunteering literature, which have developed almost independently, with limited reference to one another.Yet, both streams share an unprecedented parallel.The CE literature refers to some consumers as "brand volunteers"that is brand enthusiasts who voluntarily engage in providing unpaid contributions to forprofit organizations beyond purchase (Cova et al., 2015, p. 465).Similarly, within NPO, we contend that engaged volunteers play a dynamic role beyond what is elementary to exchange, acting both as providers and consumers, thereby co-creating value within the dyad and the broader service system.Moreover, volunteering has a dual nature, as it is recognized as a form of work as well as a form of symbolic consumption, whereby VE may represent a major part of volunteers' self-concept (Shirahada and Wilson, 2022).As such, although volunteers are not the direct recipients of the service provided by NPO, they can still be understood as consumers of the volunteering experience.Volunteers' attraction and engagement may thus be seen as a marketing challenge (Mitchell and Clark, 2021), whereby volunteers use their activities as a way of self-expression and NPO strive to match their needs (i.e. the benefits sought from volunteering) with the service offered (i.e. the volunteering experience).
Against this background, the study advances the CE literature in three ways: first, the study focuses on volunteers, that is other actors' engagement beyond the customer-brand dyad, thus contributing to the broader literature on AE (Hollebeek et al., 2022); second, since volunteers' motivation and self-determination are crucial for VE, this study further adds to the CE literature by exploring engagement from the SDT perspective, seldom adopted in prior studies (Bilro and Loureiro, 2023); third, we provide further insights on the effect of engagement on value co-creation in the non-profit sector (Alexander et al., 2018).Additionally, the study contributes to volunteering research, while adopting a marketing (instead of a human resources) perspective of VE (Curran et al., 2016).While doing so, this study extends SGT (highly popular in the CE domain) to the non-profit sector, where it has received little research attention, and validates the key (but underexplored) role of value congruence in driving VE.Lastly, while extending established theoretical frameworks to a volunteering context, this study contributes to improve the level of theorization of this research field (Traeger and Alfes, 2019).Managerially, given the significant challenges faced by the nonprofit sector and NPO's lack of theoretical and practical guidance, this study provides valuable insights for volunteer management and engagement.

Volunteer engagement and volunteering
While the concept lacks consensus (Table 1), researchers agree that volunteering can been defined as a prosocial, helping behavior that results in benefits to others.Most definitions emphasize that volunteering is a discretionary act of free will (Wilson, 2000;Penner, 2002;Petriwskyj and Warburton, 2007) that one engages without expecting any financial reward (Paço and Agostinho, 2012;Haivas et al., 2013).Some researchers view volunteering as a form of service exchange (Conduit et al., 2019), often taking place in an organizational context (Penner, 2002) that requires individuals to commit their resources beyond formal obligations (Paço and Agostinho, 2012).While some definitions have emphasized its long-term nature (Penner, 2002), volunteering is becoming more episodic and noncommittal (Traeger et al., 2022), shifting from regular to occasional, particularly among young adults (Mekonen and Adarkwah, 2022).Worldwide, 970 million individuals volunteer (Diez de Medina, 2017) and constitute a critical resource to NPO (Traeger et al., 2022) while significantly contributing to the economic, social and cultural welfare of citizens and communities (Mekonen and Adarkwah, 2022).
Even if volunteering is characterized as helping others without expecting anything in return (Wilson and Musick, 1999), volunteering is proven to be an activity that benefits volunteers psychologically, socially and physically (Wilson, 2000).Volunteers who perceive more value in their activities are expected to be more engaged with the volunteer organization (Conduit et al., 2019).Engaged volunteers invest their physical, cognitive and affective energies into their volunteer role (Alfes et al., 2016) and are more willing to stay and help the NPO beyond the call of duty (Traeger and Alfes, 2019).Yet, volunteers are also a highly volatile non-paid workforce, driven by unique personal values, beliefs and affiliation needs, who can easily lose their interest and motivation (Yoo et al., 2022) and are likely to leave the organization if they do not see sufficient value in their volunteer efforts (Traeger et al., 2022).Since NPO heavily rely on volunteers to accomplish their mission, it is crucial to explore key drivers that determine and maintain VE.
Although VE is a relatively new concept in volunteering research (Traeger and Alfes, 2019), engagement has been a topic widely discussed during the last decades in other research areas such as service management (Hollebeek et al., 2022).The first definitions of CE define it either as "psychological process" (Bowden, 2009, p. 65) or as a behavioral manifestation.For instance, van Doorn et al. (2010, p. 254) define engagement behaviors as the "customer's behavioral manifestations that have a brand or company focus, beyond purchase, resulting from motivational drivers".Since then, CE has been mostly conceptualized as a construct comprising cognitive, emotional and behavioral elements (Ndhlovu and Maree, 2022).
Author(s) Definition Wilson (2000) Any activity in which time is given freely to benefit another person, group or organization Penner (2004) A long-term, planned, and discretionary prosocial behavior that benefits strangers and occurs within an organizational context Petriwskyj and Warburton (2007) An activity undertaken with a primary purpose other than financial reward, for a common goal or the good of others, of the person's own free will and without coercion and without the intent to cause harm Paço and Agostinho (2012) The unpaid help provided in an organised manner to entities or causes with which the worker has no "formal" obligations Haivas et al. (2013) Volunteering is a freely chosen and deliberate helping activity that extends over time, one engages without expecting financial rewards nor any other compensation, often organized through formal organizations, and performed on behalf of causes or individuals who desire assistance Conduit et al. (2019) Volunteering represents a form of service exchange, offering individual resources for the benefit of other stakeholders Note(s): The studies are organized in chronological order Table 1.Overview of volunteer/ volunteering definitions in the literature JSTP 33,7 Brodie et al. (2011) further define CE as a dyadic relational exchange between a focal subject (a customer) and an object (e.g. a brand), which is context-dependent and characterized by specific intensity levels.More recently, a new research sub-stream has emerged, extending the scope of engagement to a broader range of focal actors, and covering other forms of engagement beyond the customer-brand dyad (Hollebeek et al., 2022).AE has been defined as "a dynamic and iterative process, reflecting actors' dispositions to invest resources in their interactions with other connected actors in a service system" (Brodie et al., 2019, p. 183).Since actors are resource-integrating agents that engage with a focal object in various contexts (Brodie et al., 2019;Storbacka et al., 2016), it is possible to include in this definition both the volunteer (as a subject/agent) and volunteer activities (as the focal/engagement object).
In the context of non-profit services and volunteering, engagement has been defined as "the extent to which volunteers psychologically, rather than physically, engage with their volunteer work" (Alfes et al., 2016, p. 597), and constitutes therefore a positive, motivational construct (Traeger and Alfes, 2019), with significant implications on how volunteer organizations operate (Harp et al., 2017).Engaged individuals are proud, enthusiastic and view their job as a means for self-expression (Curran et al., 2016), which is particularly valuable for non-profit services, since volunteer work is highly demanding, freely chosen and unpaid (Shantz et al., 2014).Following prior research in a volunteering context (Vecina et al., 2012;Curran et al., 2016), in this study VE is conceptualized as comprising three elements: vigor, dedication and absorption.Vigor pertains to an energetic approach to task performance, absorption relates with focus, concentration and well-being, while dedication refers to feelings of enthusiasm and endurance (Curran et al., 2016).This conceptualization is consistent with the literature on CE, where, for example Dwivedi (2015, p. 100) defines CE as "consumers' positive, fulfilling, (. ..) state of mind that is characterized by vigor, dedication, and absorption", matching (respectively) the above mentioned behavioral, emotional and cognitive aspects of CE.VE is further considered an enduring "state-of-mind" (Vecina et al., 2012), leading to increased retention, productivity and helping behaviors, such as recommending the NPO to potential volunteers and supporting volunteer recruitment efforts (Baxter-Tomkins and Wallace, 2009;Harp et al., 2017).While facing a shortage of qualified staff and increased competition, the ability to engage and retain volunteers is increasingly crucial for most NPO (Curran et al., 2016).Yet, despite the criticality of volunteers, surprisingly there is a limited understanding of why volunteers engage and co-create value with NPO (Conduit et al., 2019;Matos and Fernandes, 2021).To examine VE drivers, this study draws on SDT (Deci and Ryan, 1980), a well-known theory of human motivation.
2.2 Drivers of volunteer engagement: a self-determination approach SDT posits that different motivation types underlie human behavior (Deci and Ryan, 1980).One common approach is to make a distinction between intrinsic and extrinsic motivation (Ryan and Deci, 2000).Intrinsic motivation refers to the motivation to engage in an activity primarily for its own sake, while extrinsic motivation is associated with external incentives (Fernandes and Remelhe, 2016).Intrinsic motivation is, therefore, the prototype of self-determined behavior (Haivas et al., 2013).The basic psychological needs theory (BPNT) posits that perceived autonomy, competence and relatedness (ACR) underlie different motivation types, thus determining a person's engagement in various activities (Hsieh and Chang, 2016).Autonomy implies a need to act with a sense of volition and self-initiative, competence entails the need to feel effective and successful and relatedness captures the need of connectedness and belonging (Ryan and Deci, 2020).SDT posits that the more these needs are met, the more self-determined and free willing the behavior becomes (Haivas et al., 2013).This study draws on prior VE research (Matos and Fernandes, 2021;Conduit et al., 2019) and extant literature on CE and brand communities (Hsieh and Chang, 2016;Kelley and Alden, 2016) to examine whether these drivers can be applied to VE.We contend that volunteering activities which fulfill volunteers' psychological needs and align with their values will contribute to VE, reflecting volunteers' disposition to invest resources beyond what is elementary to exchange.Rather than merely unpaid workers, volunteers can be viewed as consumers of the volunteering experience, which is used as a way for self-expression and inner needs fulfillment.
2.2.1 Autonomy, competence and relatedness needs.According to SDT, tasks that satisfy a person's inherent psychological needs increase that person's engagement in that activity (Ryan and Deci, 2000).The level of perceived ACR is positively associated with intrinsic motivation, thus determining the degree to which an individual is willing to engage in something for its own sake (Ryan and Deci, 2020;Chiu and Nguyen, 2022), not depending on external incentives.
Similarly, in the context of CE, studies on online brand communities (OBC) concluded that customers' willingness to interact and cooperate was primarily driven by a belief in the benefit of engaging in such activities (Fernandes and Remelhe, 2016).However, although SDT has been considered a robust framework for studying CE in OBC (Bilro and Loureiro, 2023), the BPNT has received scant attention, apart from a few notable exceptions.For instance, Kelley and Alden (2016) found that consumers' innate needs (ACR) can explain their willingness to interact with OBC given their positive impact on brand engagement in self-concept, that is "consumers' propensity to include important brands as part of how they view themselves" (Sprott et al., 2009, p. 92).In a study developed during a brand co-creation contest directed at college students, Hsieh and Chang (2016) contend that if innovation activities strengthen a sense of competence (through, e.g.obtaining new skills), relatedness (through, e.g.connecting with others) and autonomy (through, e.g.allowing independence), students are likely to be internally motivated to participate, which will promote high engagement levels.Other studies used the BPNT to predict outcomes related to CE (Gilal et al., 2019), such as customer attachment to brands (Hung, 2014) and celebrities (Thomson, 2006).
In the context of volunteering, a few authors have successfully applied SDT and BPNT to research on volunteers' motivation.Studies have shown that the more volunteers feel they are effective (competence) and the source of their own volunteering behavior (autonomy), the more they develop work engagement and the less they will consider leaving volunteering organizations (Haivas et al., 2013).As autonomy reflects the extent to which a job allows freedom and discretion to choose work methods and make decisions, it enhances volunteers' joy and interest for the volunteering activity itself (van Schie et al., 2015).Moreover, while using their competencies and doing something at which they are good at, volunteers may feel they are getting something in return from their work, motivating them to stay and engage with the NPO (Haivas et al., 2013).Accordingly, Matos and Fernandes (2021) found that the positive feedback given to the volunteer by the NPO and/or its beneficiaries leverages a sense of competence and plays a crucial role in engagement.Similarly, Brodie et al. (2019) concluded that when volunteers perceive the impacts of their actions on others' lives, they find it rewarding, thus enhancing their engagement levels.The possibility to connect with other people (inside and outside the NPO) has also been considered a crucial component of the volunteer experience.For instance, Millete and Gagn e (2008) and Shantz et al. (2014) found that promoting interactions between volunteers and beneficiaries can leverage engagement among volunteers.Additionally, when volunteers share their experiences with their fellow members or personal relationships are developed among volunteers (Harp et al., 2017), a sense of belongingness to a community is likely developed (Matos and Fernandes, 2021), leading to higher levels of engagement.As such, we posit that: H1.The level of (a) autonomy, (b) competence and (c) relatedness perceived by volunteers has a positive effect on VE.
JSTP 33,7 2.2.2The mediating role of value congruence.When joining an NPO, most volunteers bring high self-determined motivations, closely related with their inherent psychological needs, which will help them to fulfill core volunteer activities and achieve psychological wellbeing.However, the simple joy of being a volunteer may not be sufficient to preserve their high self-determined motivation and engagement (van Schie et al., 2015), as sustained volunteerism may result from both dispositional and organizational factors (Nencini et al., 2016).Volunteerism often occurs within an organizational context, and the internalization of organizational values may play a key role in sustaining volunteer motivation and promoting an efficient and effective functioning of the NPO.Organizational identification describes the extent to which volunteers internalize organizational membership in their self-concept (Traeger and Alfes, 2019) and perceive the NPO as an integral part of their being (Ashforth and Mael, 1989).This internalization process is reflected in the way volunteers express themselves when they speak about their NPO (as "we" instead of "they") and leads volunteers to demonstrate devotion to their activities by increasing their engagement.This is consistent with Kahn (1990), who states that "it is difficult for people to engage personally in fulfilling work processes when organizational ends do not fit their own values" (p.716).Accordingly, in a public service context, Wright and Pandey (2008) claim that employees show more motivation, satisfaction and performance once they perceive value congruence or "that his or her values are congruent with those of the [. ..] organization he or she works for" (p.502), that is there exists a compatibility between individual characteristics and those of the organization such as culture, mission, purpose and norms.
In the CE literature, this phenomenon is termed self-congruity, and is described as a "mental comparison that consumers make in respect to the similarity or dissimilarity of entity's values and their own set of values" (Tu skej et al., 2013, p. 54).Mostly applied in the field of branding, SGT (Sirgy, 1985) explains consumers' tendency to prefer brands congruent with their own self-image.Congruency between the consumer and the brand implies a strong brand identification, with consumers often integrating brands into their self-concept to build their social identities (Ashforth and Mael, 1989).Prior research has found a strong connection between CE, self-congruity and brand identification.Kumar and Nayak (2019) state that selfcongruity or value congruence represents an important psychological motivation for customers' engagement with brands, whereas Bowden et al. (2016) found a positive relationship between shared values and engagement.Similarly, France et al. (2016) demonstrated that customers with high self-congruity also display high engagement levels.Prentice et al. (2019) validated identification with an OBC as a self-driven precondition for customers to volitionally engage with the brand and the community.In their study on brand co-creation engagement, Hsieh and Chang (2016) refer to self-brand connection and validate it as the strongest driver of CE.When customers establish a connection with the brand that supports the co-creation task, they incorporate it into their self-concept and feel motivated to engage in brand co-creation.
In the context of volunteering, this logic also applies, with the expression of personal values being repeatedly found to be an important driver of VE (Vecina et al., 2012).Matos and Fernandes (2021) found that the identification with NPO values was elected as one of the main causes for VE.Value congruence was also shown to drive individuals' readiness to volunteer for NPO (van Schie et al., 2015), whereas Penner (2004) and Baxter-Tomkins and Wallace (2009) claim that for VE to exist it is important that the organization and its volunteers share the same values.If volunteers deem NPO values and characteristics as congruent with their own values and characteristics¸involvement in the volunteering organization would represent a major part of their self-concept.However, self-congruity has been scarcely investigated in non-profit services, apart from some notable exceptions (e.g.Randle and Dolnicar, 2011).In this study, we contend that: H2.Value congruence between volunteers and the NPO has a positive effect on VE.
From an SDT viewpoint, when customers identify with an object (e.g. an NPO) and fully assimilate it with the self, the last stage of the motivational processthe internalization stageoccurs (Ryan and Deci, 2000).SDT suggests that, regardless of individuals' original motives, they will seek objects that reflect their self-concept, which will strengthen their identification and allow them to move through the internalization process, explaining higher engagement levels (Kelley and Alden, 2016).As such, self-congruence acts as an internalizing mechanism (Deci and Ryan, 2000) that transfers inner needs fulfillment into a person's engagement, or attachment with the self-congruent object.In a marketing context, this internalization process was validated by Hung (2014) while using the three basic psychological needs to predict customers' attachment to brands, an outcome closely related to CE.The author concluded that brand self-congruence mediates this relationship, while transforming customers' motivations into inner values.When the brand engenders positive associations in consumers' minds that satisfy their self-determination needs, consumers identify with the brand and integrate it with their sense of self, thus triggering brand attachment (Hung, 2014).According to Shulga and Busser (2021) when a brand contributes to satisfy their basic innate needs, customers demonstrate increased connection and alignment with the brand, leading them to engage more intensively and frequently with the community.Similarly, Milliman et al. (2003) argue that performing activities that align the fulfillment of volunteers' needs with their values is likely to engender VE.In a similar vein, Wright and Pandey (2008) found that the relationship between public servants' motivation (including altruistic dimensions such as public interest, compassion and self-sacrifice) and job satisfaction is mediated by the extent to which public servants perceive that their values are congruent with those of the public sector organization they work for.As such, the authors claim that "public service motivation's influence on employee attitudes and behaviors beneficial to the organization may be indirect, mediated through its effect on employee-organization value congruence" (p.508).Yet, in a volunteering context, this mediating role of value congruence has only been implied (e.g.van Schie et al., 2015) but not empirically tested.Against this background, it is hypothesized that: H3.Value congruence between volunteers and the NPO mediates the effect of the level of autonomy, relatedness and competence perceived by volunteers on VE.

Outcomes of volunteer engagement: a service-dominant logic approach
Early research establishes that CE contributes to the core relationship marketing tenets of customer repeat patronage, retention and loyalty (van Doorn et al., 2010).However, the impact of CE on other non-transactional outcomes such as co-creation has been gaining increasing attention (Hollebeek et al., 2019).Indeed, a fundamental proposition of engagement is that it occurs within a dynamic, iterative process that co-creates value (Brodie et al., 2013).Co-creation can be defined as "an interactive process, involving at least two willing resources integrating actors, which are engaged in specific form(s) of mutually beneficial collaboration, resulting in the value creation for those actors" (Frow et al., 2011, p. 1).According to van Doorn et al. (2010), co-creation occurs when the customer participates through spontaneous, discretionary behaviors beyond the selection of predetermined options.Similarly, CE includes voluntary, extra-role behaviors that an actor is willing to perform beyond the call of duty, driven by its own unique purposes and intentions (Jaakkola and Alexander, 2014).While sharing common characteristics (Conduit and Chen, 2017), CE and co-creation are intrinsically connected, whereby co-creation has been established as one of the manifestations of engagement (Fernandes and Remelhe, 2016).Engagement is particularly relevant due to the potential behaviors resulting from actor-to-actor interactions, namely the co-creation of value that can emerge.

JSTP 33,7
As a conceptual foundation for the development of the CE concept (Brodie et al., 2011), SDL (Vargo and Lusch, 2004) provides a general theoretical perspective to better understand the association between engagement and value co-creation (Hollebeek et al., 2019).According to this perspective, value is not produced and delivered but always co-created (Conduit et al., 2019).As such, SDL considers value a jointly, co-created phenomenon that emerges through resource exchange and integration during actor-to-actor interactions (Vargo and Lusch, 2008) taking place in complex and dynamic network structures, or service systems (Vargo and Lusch, 2011).AE can thus be seen as a resource integration behavior in the value co-creation process: without AE, no resource integration happens, and no value can be co-created (Storbacka et al., 2016).Past research indicates that, through non-transactional engagement behaviors, customers may co-create value by contributing a broad range of resources within their own networks, to actors beyond the provider-customer dyad (Jaakkola and Alexander, 2014).Engagement behaviors are characterized as "an actor's voluntary resource contributions that focus on the engagement object, go beyond what is elementary to the exchange, and occur in interactions with a focal object and/or other actors" (Alexander et al., 2018, p. 336).The CE literature has mainly focused on two types of engagement behaviors: customer involvement in product development and innovationthrough augmenting and co-development behaviorsand customers' communication about the focal firm or brandthrough influencing and mobilizing behaviors (Jaakkola and Alexander, 2014).These behaviors have been identified as manifestations of CE associated to value co-creation.
In the context of volunteering, outcomes of VE have also been discussed.For NPO, co-creation relates to the exchange and integration of resources aimed to create social value between the organization and its ensemble of actors (Namisango et al., 2021), including donors, beneficiaries and volunteers.Yet, although it is reasonable to expect that engaged volunteers may be willing to perform beyond the call of duty through discretionary behaviors that (favorably) extend beyond formal role requirements (Bettencourt, 1997), volunteering research has overlooked volunteer co-creation engagement behaviors (Yoo et al., 2022) and has instead been extensively focused on volunteers' retention as the main outcome of VE.This is surprising since, in a volunteering context, individuals "actively decide to commit their resources (e.g.time and skills) to the benefit of a third party (i.e. the volunteer recipient); but where value is also created for the volunteer as well as for the volunteer organization" (Conduit et al., 2019, p. 463).Notable exceptions include studies developed by Baxter-Tomkins and Wallace (2009), on recruiting volunteers in emergency services, and Yoo et al. (2022) on VE in sport events, as well as Matos and Fernandes' (2021) qualitative research on the impact of VE on value co-creation.As such, co-creation behaviors resulting from VE deserve more research attention.
2.3.1 Volunteers' loyalty to the NPO.NPO operate in a competitive environment (Curran et al., 2016), where retaining engaged volunteers is crucial to maintain their regular activities.The positive relationship between VE and volunteer retention has been established in prior studies.VE has been associated to volunteers' satisfaction and happiness, which in turn should prevent them from leaving the NPO (Alfes et al., 2016;Malinen and Harju, 2017).Similarly, Shantz et al. (2016) validated a direct and reverse relationship between VE and the intention to leave the NPO.
In the extant CE literature, the impact of engagement on customer retention has also been established.However, given its interactive and immersive nature (Brodie et al., 2011), CE may further generate an enduring psychological connection with the focal engagement object, which will consequently make customers feel more loyal to the entity (Dessart et al., 2015;France et al., 2016).In his seminal work, Oliver (1999, p. 34) defines loyalty as "a deeply held commitment" to repatronize a preferred brand "despite situational influences and marketing efforts having the potential to cause switching behavior".Accordingly, loyalty encompasses not only retention and repeat purchasesusually referred to as "behavioral loyalty"but also positive internal dispositions towards the brand (Vivek et al., 2012) usually referred to as "attitudinal loyalty" (Jahn and Kunz, 2012).Loyalty entails commitment, that is an implicit or explicit pledge to the continuity of a relationship (Wetzels et al., 1998), with the committed party believing that the relationship is worth working on to ensure it endures indefinitely (Morgan and Hunt, 1994).
Extending these findings to a volunteering context, it is reasonable to expect that engaged volunteers will not only be less likely to defect but will also feel more loyal to the NPO, which can be demonstrated by the time spent and the effort developed by volunteers while performing their tasks (Shantz et al., 2014).Yet, prior volunteering studies have been extensively focused on volunteer retention as VE's main outcome (Yoo et al., 2022).Drawing on early CE studies (e.g.Vivek et al., 2012) which state that engagement engenders increased loyalty, we present the following hypothesis: H4. VE has a positive effect on volunteers' loyalty to the NPO.

Volunteers' intention to recommend the NPO.
Other extra-role, engagement behaviors may be expected when volunteers present high levels of engagement, such as spreading positive word-of-mouth (Yoo et al., 2022), influencing stakeholders' perceptions and inducing concrete actions toward the focal firm, such as recruiting other citizens and fund raising.These influencing and mobilizing behaviors have been identified as manifestations of CE directed to other customers (Roy et al., 2020) and associated to value co-creation (Jaakkola and Alexander, 2014).The authors define influencing behavior as "customer contributions of resources such as knowledge, experience, and time, to affect other actors' perceptions, preferences, or knowledge regarding the focal firm" and mobilizing behavior as "customer contributions of resources, such as relationships and time, to mobilize other stakeholders' actions toward the focal firm" (p.256).In the same vein, Brodie et al. (2013) refer to "advocating" as an expression of CE, which occurs when "consumers actively recommend specific brands, products/services, organizations, and/or ways of using products or brands" (p.111).These advocates spend time and effort to recommend, promote or support a brand, which is seen as a "discretionary activity" or "extra-role behavior" (van Doorn et al., 2010).These behaviors not only enhance brand reputation and recognition (Gong and Yi, 2021), but also have the potential to influence and mobilize other stakeholders (Alexander et al., 2018).It has been proven that individuals with high engagement levels are more likely to recommend their organization and its offerings, or as an employer (Kumar and Nayak, 2019).Additionally, recommendations are considered one of the most powerful CE tools to conquer new customers (Kumar et al., 2010).Yi and Gong (2013) have considered advocacythat is recommending the business to others such as friends or familyas a completely voluntary behavior contributing to value co-creation.In a volunteering context, Baxter-Tomkins and Wallace (2009) examine the willingness of volunteers to recruit and mobilize other volunteers, while Yoo et al. (2022) study volunteer's willingness to spread positive word-of-mouth about the organization to other potential volunteers.Matos and Fernandes (2021) found that most volunteers were in fact recruited through other volunteers' recommendations.As such, we posit that: H5. VE has a positive effect on volunteers' intention to recommend the NPO.

Volunteers' willingness to help develop new NPO offerings.
There are other behavioral outcomes resulting from engagement, such as contributing to develop organizational offers, or codeveloping behaviors.Jaakkola and Alexander (2014) define augmenting behavior as "customer contributions of resources such as knowledge, skills, labor, and time, to directly augment and add to the focal firm's offering beyond that which is fundamental to the transaction" (p.254) and co-developing behavior as "customer contributions of resources such as knowledge, skills, and time, to facilitate the focal firm's development of its offering (p.255).Co-developing behaviors JSTP 33,7 are also mentioned by Brodie et al. (2013, p. 111) as "a process where consumers contribute to organizations and/or organizational performance by assisting in the development of new products, services, brands or brand meanings".For instance, clients can give ideas for new or improved products or services, thus becoming one of the most valuable sources of information for managers (Gong and Yi, 2021;Fernandes and Cruzeiro, 2022).By providing new information through feedback, suggestions and sharing ideas (Alexander et al., 2018;Kumar and Pansari, 2016), engaged actors can contribute to the development of organizational offers.Knowledge sharing can offer solutions for future product modifications, improvements or updates.Yi and Gong (2013) have considered feedbackthat is solicited and unsolicited information that customers provide to the firm to improve the service creation process-as a valuable extra-role, co-creation behavior direct towards the organization (Roy et al., 2020).Similarly, Alves et al. (2016) agree that development of new products and services is one of the major factors associated with value co-creation.
In a volunteering context, Yoo et al. (2022) examined the role of VE in driving volunteers' willingness to provide suggestions that can help organizations and event managers to better understand the needs and preferences of their volunteers and improve the work environment.Similarly, Matos and Fernandes (2021) confirmed that high levels of VE contribute to the development of new services by volunteers and to the expansion of NPO's offer.Against this background, the following hypothesis is proposed: H6. VE has a positive effect on volunteers' willingness to help develop new NPO offerings.
Moreover, the relationship between loyalty and extra-role, engagement behaviors such as influencing, mobilizing or co-developing can be seen as a cause-effect cycle.Drawing on social exchange theory (Blau, 1964), highly loyal and engaged individuals which identify with an organization's purposes and core values are interested in the welfare of the organization (Yi and Gong, 2008).As such, they are willing to invest in a relationship they believe is worth working on through extra-role, discretionary behaviors (Bettencourt, 1997).Considering that these behaviors are "an act of loyalty", it is reasonable to expect that loyalty may act as a precursor of the other two outcomes: H7. Volunteers' loyalty has a positive effect on their intention (a) to recommend the NPO and (b) to help develop new NPO offerings.
Accordingly, Figure 1 depicts the research framework.

Research methodology
To test the research hypotheses, a survey method was adopted to describe and interpret the relationships among existing variables.In line with purposive sampling techniques, a sample of volunteers working with NPO was invited to participate in a web-based, cross-sectional survey.NPO were contacted through email and social media and asked to share the survey with their volunteers' database.Participation was voluntary and anonymous.When starting the questionnaire, respondents were instructed to consider the NPO with which they worked, or to choose the one with which they were more involved with in case they were cooperating with several NPO.Respondents then completed the survey with reference to the NPO they had selected, which included food banks, disability services, organizations working for institutionalized children, homeless and elderly people, drug users, abandoned pets, among others.The full questionnaire was made available through a web link, taking roughly five minutes to complete.The questionnaire had 32 mandatory questions based on multi-item scales previously established in the literature, assessed in a seven-point Likert scale, ranging from "totally disagree" to "totally agree" (Table 3).Scales adapted from van den Broeck et al. (2010) were used to measure autonomy and relatedness perceptions, conceptualized as feelings of volition and connectedness with other volunteers, respectively.Three items borrowed from Hsieh and Chang (2016) were used to measure perceived competence, which refers to a sense of effectiveness while performing volunteer activities.Based on three items borrowed from Dwivedi (2015), VE was operationalized as the vigor, dedication and absorption demonstrated by volunteers during task performance.Loyalty was measured with items borrowed Jahn and Kunz (2012), based on both its attitudinal and behavioral components.Three items borrowed from Kumar and Pansari (2016), Harrison-Walker (2001) and Yi and Gong (2013) were used to measure the willingness to recommend the NPO and to develop new NPO offerings.Finally, value congruence refers to the extent to which volunteers identify and perceive the NPO as an integral part of their self-concept and was measured with a four-item scale adapted from Hsieh and Chang (2016) and Kumar and Nayak (2019).Information on demographics was also collected, as well as the duration and frequency of respondents' volunteer activities.
Overall, 484 respondents participated in the survey.After removing inappropriate responses (e.g.identical answers to all questions) and respondents who claimed being volunteers for less than a month, 450 answers were validated (Table 2).Respondents' ages spanned from 18 to 78 years old, with 45.6% at 32 years old or less.Moreover, respondents were predominantly (72%) women.Most respondents (64.7%) dedicate 4-16 h per month to volunteer activities, with 40% performing them regularly (3-4 times per month) for at least one year (64%).
To reduce potential common method bias (CMB), the survey used existing scales, counterbalanced the order of the measurement variables and ensured the respondents' anonymity (Podsakoff et al., 2012).Additionally, CMB was examined by performing the Harman's single-factor test (Harman, 1976), which demonstrated that none of the factors accounted for most of the covariance among items.
Partial Least Squares Structural Equation Modelling (PLS-SEM) using the Smart PLS 3.0 software (Hair et al., 2014) was employed.PLS-SEM is a modelling technique well-suited for assessing complex predictive models (Hair et al., 2014) and for the theory building stages of an exploratory study (Roy et al., 2020) and was thus deemed appropriate for this study.Moreover, PLS-SEM enjoys increasing popularity given its ability to model latent constructs even for conditions of non-normality, placing minimal demands on sample size (Hair et al., 2014).The advocated two-step procedure of evaluating the measurement (outer) model first, followed by an estimation of the structural (inner) model was adopted (Anderson and Gerbing, 1988).(Nunnally, 1978).All factors display good internal consistency and high levels of convergence (Table 3) exhibiting strong Cronbach's alpha, as well as Composite Reliabilities and Average Variances Extracted above recommended minimums of 0.70 and 0.50 (Fornell and Larcker, 1981).
Convergent and discriminant validity are demonstrated by factor loadings, and by the latent constructs correlations and the square root of their specific Average Variances Extracted (AVE), respectively.All factor loadings for indicators measuring the same construct are statistically significant (p < 0.01), supporting convergent validity.Moreover, estimated pairwise correlations between factors do not exceed 0.85 and are significantly less than one (Bagozzi and Yi, 1988); and the square root of AVE for each construct is higher than the correlations between them (Anderson and Gerbing, 1988), supporting discriminant validity (Table 4).After establishing the strength and psychometric properties of the scales underpinning the model, the degree of multicollinearity among the model variables was examined through the variance inflation factor (VIF).Values vary from 1.766 to 2.575, which is below the common cut-off threshold of 5 (Hair et al., 2014) and suggesting that the factors are not highly correlated to one another.

Structural model
The structural model (Figure 2) was estimated through a bootstrap resampling tool to determine path significances.Regarding total effects (i.e.without controlling for mediating effects), results provide support for H1 and H2, with a significant positive effect of perceived autonomy (β 5 0.361), perceived competence (β 5 0.328), perceived relatedness (β 5 0.147) Volunteer engagement and value congruence (β 5 0.322) on VE.Support was also found for H4, with a significant, positive relationship between VE and loyalty to the NPO (β 5 0.599), which in turn has a positive effect on the intention to recommend the NPO (β 5 0.667) and the willingness to develop new offerings (β 5 0.529), thus validating H7.Regarding total effects, results provide support for H5 and H6, with a significant positive effect (both direct and indirect) of VE on the intention to recommend the NPO (β 5 0.543) and to develop new offerings (β 5 0.444).

Mediation analysis
We have also tested the mediating role of value congruence on the link between ACR needs and VE (H3).Full mediation is supported if the indirect effect is significant, and the direct effect is non-significant (Zhao et al., 2010).A bootstrapping procedure (Preacher and Hayes, 2004) based on 3,000 samples, validates the indirect effects (mediated by value congruence) of perceived autonomy (β 5 0.134, p 5 0.000), competence (β 5 0.098, p 5 0.009) and relatedness (β 5 0.102, p 5 0.000) on VE (Table 5).Self-determined motivations (ACR) have a significant and positive impact on value congruence, which in turn significantly influences VE (β 5 0.322).While direct effects on VE remain significant for perceived autonomy (β 5 0.227) and competence (β 5 0.230), there is a non-significant direct effect between perceived relatedness and VE (β 5 0.045; p 5 0.362), indicating partial and full mediation (respectively), Volunteer engagement and thus confirming H3.Overall, the structural model explains 48.4% of the variance in VE, 54.6% of value congruence, 57.6% of the intention to recommend the NPO, 48.2% of the willingness to develop new NPO offerings and 35.9% of the loyalty to the NPO.

Alternative models
Given that our research is cross-sectional in nature, we have tested if an alternative model could fit the data equally well (Bagozzi and Yi, 1988).Although we have provided theoretical and empirical support for considering value congruence as an internalizing mediating mechanism in the VE process, in the alternative model value congruence will be treated as a variable moderating the relationship between fulfilling a volunteer's basic needs and developing VE.The results show that the moderating effect of value congruence on the relationship between VE and autonomy (β 5 À0.051, t 5 1.448, p 5 0.148), competence (β 5 À0.070, t 5 1.460, p 5 0.144) and relatedness (β 5 À0.081, t 5 1.481, p 5 0.139) needs was not significant; as such, the data did not support this alternative model.
To further confirm the robustness of the proposed model, we have tested if a less complex model considering loyalty as the sole precursor to the intention to recommend the NPO and to develop new offerings (i.e.accounting only for an indirect effect of VE) was preferable.PLSpredict is ideal for the empirical comparison of competing models with the same endogenous dependent constructs (Roy et al., 2020).The superior model minimizes the out-ofsample error statistics such as MAE (mean absolute error) and RMSE (root mean squared error) (Shmueli et al., 2019).Model comparison results (Table 6) show that the original model exhibits lower prediction errors in the ultimate dependent variables (i.e.extra-role behaviors) and is thus superior to the alternative model.Moreover, the total variances explained for the intention to recommend (0.576 vs 0.562) and develop new offerings (0.482 vs 0.470) were higher in the original model than in the alternative one.Thus, we contend that the original model is meaningful and robust.

Discussion
This study aimed to understand what motivates volunteers to engage with the volunteer organization in the value co-creation process.Grounded on SDL, SGT and SDT, a model of drivers and outcomes of VE was empirically tested.The model considered the three basic psychological motivations (ACR) as drivers of VE, while also examining the role of value congruence as an internalizing mediating mechanism in the engagement process.Research posits that, when volunteers' basic innate needs are met and align with their values, they will feel more engaged with their volunteering activities, leading not only to volunteer retention, but also to perform beyond the call of duty by contributing their own resources to co-create value with the NPO and the broader service system.
Overall, the study supports most of the research hypotheses.First, findings validate the positive effect of volunteers' perceived autonomy, competence and relatedness (H1) on VE.Considering the three psychological needs, autonomy and competence emerged as the two main drivers of VE.Hence, results indicate that VE is highly self-and task-oriented: when volunteers satisfy their autonomy and competence needs by perceiving themselves as being the source of their own behavior and applying their skills to overcome taskrelated challenges, they will show a higher degree of engagement.While BPNT has received scant attention in the engagement domain, results contradict Hsieh and Chang's (2016) study, where perceived relatedness emerged has the main driver of students' engagement in a university contest but are in line with studies developed in a volunteering context, which validated autonomy and competence as the most influential determinants of VE (Haivas et al., 2013) and volunteer retention (Conduit et al., 2019), a well-established outcome of VE. Results also corroborate Ryan and Deci's (2000) cognitive evaluation theory, a sub-theory of SDT, which focuses on the fundamental needs of autonomy and competence as highly salient for producing intrinsic motivation, while relatedness needs should play a less determining role in the process.While autonomy and competence work in tandem to determine a person's engagement in various activities, relatedness alone may not be enough to ensure autonomous, self-determined behavior (Haivas et al., 2013).
Second, the study validates the role of value congruence as an internalizing mechanism in the engagement process (H2) that mediates the relationship between fulfilling volunteers' needs and developing VE (H3).Although little attention has been given to SGT in this context, engagement with volunteering activities represents a fundamental part of one's self-concept, with individuals acquiring symbolic value by consuming the "opportunity to volunteer" (Shirahada and Wilson, 2022).Self-concept is particularly relevant to volunteers, and it might manifest itself as belonging to a particular cause or organization, "the values and characteristics of which they consider consistent with their own characteristics and abilities" (Randle and Dolnicar, 2011, p. 742).In the current study, respondents clearly expressed how the NPO reflects their self-concept or how they identify with the NPO (with mean scores (Table 3) ranging from 5.23 to 6.05).When volunteers internalize organizational membership in their self-concept and thus perceive the NPO as an integral part of their being, they will be more devoted to their activities by increasing their engagement (Traeger and Alfes, 2019).In their qualitative study, Matos and Fernandes (2021) identified the alignment with the organization's values ("It's identifying myself with the values of the NPO (. ..) otherwise, I would not feel as willing to engage in those activities"; "I also found a lot of sense (. ..) with organizations that have values identical to mine"; "They have volunteering values with which I agree 100%, and I totally identify with their purpose") as one of the main precursors of VE.Within the CE domain, this relationship has been established by prior studies (e.g.France et al., 2016;Prentice et al., 2019), with Hsieh and Chang (2016) identifying brand-self congruence as the strongest driver of CE.Our study validates the role of congruence as, at least, a partial mediator linking the three motivational needs to VE. Although, to the best of the authors' knowledge, this relationship has not yet been testedneither in a volunteering context nor in the CE literatureit corroborates that self-congruence acts as an internalizing mechanism (Deci and Ryan, 2000) that transfers inner needs fulfillment into a person's engagement with the self-congruent object.Hence, the more motivated and self-determined volunteers are, the more likely they are to engage in volunteering, thanks to the alignment with the values of an organization that makes them feel autonomous and competent, and experience a sense of belonging, thus fostering a "we"-sense (Jahn and Kunz, 2012, p. 353) to the NPO.
Notably, the study concludes that this internalization mechanism is centrally important when it comes to relatedness, since this need only significantly impacts VE indirectly through value congruence.The organismic integration theory (OIT), a second sub-theory of SDT (Ryan and Deci, 2000) dedicated to factors that promote or hinder internalization, explains these findings.OIT proposes that internalization is more likely to be in evidence when the context (e.g. the organizational environment) supports feelings of relatedness, developed from a sense of community and connectedness with others (Ryan and Deci, 2000).Unlike autonomy and competence needs, which are more inner/individually oriented, relatedness needs are more extrinsically or social-oriented.While working as a team, partaking in the same activities, and sharing experiences, volunteers develop a meaningful sense of belonging to a group, which gives rise to full integration of their values as part of an individual's self-concept.In this sense, organizational support for relatedness allows individuals to actively transform NPO values into their own (Deci and Ryan, 2000) sustaining their self-determination to engage in volunteering activities.Volunteers participating in Matos and Fernandes' (2021) qualitative study emphasize this idea, while claiming that "it is very important for a NPO to have a social environment among volunteers . . .a feeling of family" or that "from the moment I felt part of a group, my self-concept and identity were highly reinforced".This rationale may help to explain why prior volunteering studies failed to find a significant effect of relatedness on VE (Haivas et al., 2013) and retention (Conduit et al., 2019), since no consideration was given to congruence as an internalization mechanism, essential for many of the optimal outcomes associated with the satisfaction of affiliation needs to occur (Ryan and Deci, 2000).This mechanism seems to be key when feelings of connectedness result from the bonds established with other volunteers (the focus of this study) but may also apply when considering interactions with people outside the NPO (e.g. the beneficiaries).
Lastly, this research validates the positive effect (direct and indirect) of VE on desirable outcomes such as loyalty to the NPO (H4), the intention to recommend the NPO (H5) and the willingness to develop new NPO offerings (H6), with loyalty acting as a precursor of the other two outcomes (H7).Although prior volunteering studies have been extensively focused on volunteers' retention as the main outcome of VE (Yoo et al., 2022), the study extends prior CE literature grounded on SDL (Vargo and Lusch, 2004) to show that volunteers may develop other extra-role, engagement behaviors, such as influencing, mobilizing and co-development behaviors, identified as manifestations of CE associated to value co-creation (Jaakkola and Alexander, 2014;Roy et al., 2020).Hence, a state of "self-concordance" (Deci and Ryan, 2000, p. 239), in which engagement in NPO activities is in harmony with volunteers' needs and values, encourages them to exchange and integrate their own resources beyond the call of duty, creating value for the benefit of the NPO and the broader service system (Conduit et al., 2019).

Conclusions 6.1 Theoretical contributions
The study contributes foremost to two research streamsthe literature on engagement and service management, as well as the literature on volunteering and non-profit serviceswhich despite an unprecedented parallel have developed almost independently, with limited reference to one another, thereby creating new knowledge in both domains.
Notably, the study contributes to the engagement and service management literature, mostly focused on the customer-brand dyad and on for-profit contexts (e.g.Dessart et al., 2015;Hollebeek et al., 2019), but where other actors' engagementsuch as volunteersand non-profit services remain understudied (Hollebeek et al., 2022).Against this background, our contributions to the engagement and service management literature are threefold.First, by extending the CE literature to the volunteering sector, a networked setting involving multiple actors (Brodie et al., 2019), this study bridges what is already known for commercial brands JSTP 33,7 with the specific challenges of this new context, thus contributing to the broader literature on AE.Second, considering that volunteers are a volatile non-paid workforce driven by unique personal values and affiliation needs, this research draws on SDT and BPNT to better understand how to generate a sense of engagement among volunteers.Although SDT has been considered a robust framework for studying CE (Bilro and Loureiro, 2023), it has received scant attention, apart from a few notable exceptions (e.g.Hsieh and Chang, 2016).Third, the study provides further insights on the impact of engagement on behavioral manifestations contributing to value co-creation, where additional research is still needed (Alexander et al., 2018).As few studies have considered the role of engagement in value co-creation, the study addresses prior calls to test hypotheses derived from Jaakkola and Alexander's (2014) propositions regarding engagement behaviors in a wider range of contexts, such as non-profit services.While validating the impact of autonomy, competence and relatedness on VE, this study shows how self-determination factors can influence co-creation (Shulga and Busser, 2021), thereby lending support to CE researchers who claim that engagement drivers may not only be extrinsic (e.g.brand-related) but originate from the customers themselves (Jaakkola and Alexander, 2014).
Additionally, the study contributes to research on volunteering and non-profit services where studies on VE are scarce (Yoo et al., 2022), particularly from a volunteers' point of view (Conduit et al., 2019).Our contributions to this research stream are threefold.First, this study extends the CE literature regarding brands, OBC and engagement behaviors to a volunteering context.Unlike prior volunteering literature, which has mostly adopted a human resources management approach to engagement, this study adopts a marketing perspective of VE (Curran et al., 2016).Accordingly, this study views volunteers' attraction and engagement as a marketing challenge (Mitchell and Clark, 2021), whereby volunteers use their activities as a way of self-expression (Shirahada and Wilson, 2022) and NPO strive to match their needs during the volunteering experience (Randle and Dolnicar, 2011).As such, while examining VE through new marketing lenses, this study contributes to a better understanding of engagement and branding within NPO.Second, drawing on SGT and SDL, seldom applied to non-profit services, research identifies value congruence as a key (but underexplored) driver and internalizing mediator underlying the VE process.The study concludes that VE contributes not only to volunteer retentionthe focus of prior studiesbut also to co-creation engagement behaviors performed by volunteers beyond the call of duty.Therefore, as it happens with "brand volunteers" (Cova et al., 2015), engaged volunteers can be seen as active "members" of volunteering organizations, who are willing to commit their resources to co-create value, benefitting not only themselves, other volunteers and beneficiaries, but also the NPO, through, for example developing new offerings and recruiting new members.Third, while extending established theoretical frameworks to a volunteering context, this study contributes to improve the level of theorization of this research field (Traeger and Alfes, 2019).

Managerial implications
Non-profit services play a relevant role in society at large, but also face significant challenges for which practical guidance is needed.This study addresses some of these needs while providing NPO valuable insights for volunteer management.We contend that NPO should approach volunteers' attraction and engagement not only as a recruitment issue but also as a marketing challenge, and hence strive to create the best match between the volunteering experience offered and the needs and values of individuals.
Findings reveal volunteers' basic needs (ARC) and value congruence as drivers of VE.When joining a particular organization, volunteers are expected to bring high self-determined motivation to fulfill volunteer activities closely related to their personal goals.But while volunteers' self-determination is key to develop VE, the organizational context can either enable or hinder their needs' satisfaction process (Shulga and Busser, 2021;Nencini et al., 2016).Its characteristics are not only crucial to sustain volunteers' motivation but can also help them to the fulfill their needs and to incorporate NPO values into the self, which in turn will facilitate the internalization process that leads to VE.Given that volunteering is an act of free will, this process is essential to NPO, which lack the means to control their workforce and must rely on volunteers' willingness to comply and integrate organizational rules and core values, such as their mission and culture.
SDT states that one of these organizational factors is an autonomy supportive leadership (Shih et al., 2022), which is expected to nurture self-determined motivations.Autonomy supportive supervisors show interest in the volunteers' perspective, provide opportunities for choice and input and encourage self-initiation.NPO supervisors are thus advised to, for example include volunteers in decision-making or allow them to choose the projects in which they want to be involved.An environment that supports individual's autonomy offers an opportunity to higher engagement in the task, longer time spent and better attitudes toward the task (Shulga and Busser, 2021).
As volunteers perceive themselves as regulators of their own behavior, they will experience a high sense of empowerment, which will make them feel more autonomous and competent in carrying out their tasks (Traeger and Alfes, 2019).Training and guiding volunteers to have the right skills to perform tasks by themselves should thus be a top priority for NPO.Additionally, tasks should be designed to enhance its motivational potential, another important organizational factor.The diversity and significance of tasks should enhance volunteers' joy and interest for the volunteering activity itself (van Schie et al., 2015) which in turn benefits their vigor, absorption and dedication.Performance appraisals, verbal support and feedback should also be provided to volunteers so they can feel competent in their activities.Such feedback can come directly from the NPO or from their beneficiaries (Matos and Fernandes, 2021).Lastly, NPO supervisors should also clarify how volunteer activities are helping the wider community.NPO managers should also consider the development of activities to promote the interaction among volunteers, contributing to a sense of belongingness to the NPO, which can contribute not only to leverage perceived relatedness but also value congruence.Such activities could range from workshops to collective sharing experiences or making volunteers work together.Correct integration of new volunteers should be prioritized as older volunteers can have an active role in the integration process and in harmonizing the values of new volunteers to the ones of the NPO.This would allow a "a we"-sense to be fostered within the NPO.
As volunteers feel that the NPO cares about them and supports their needs' satisfaction, they will respond by increasing their identification and alignment with the organization and thus contribute to NPO goals as if they were their own (Traeger and Alfes, 2019).The degree to which organizational contexts allow the fulfillment of basic psychological needs impacts volunteers' ability to incorporate NPO values into the self, thus facilitating the internalization process.While representing the organization, supervisors may promote volunteers' sense of congruence and contribute to the internalization of NPO rules, as well as a clear and coherent communication of organizational values.Whilst preserving their core values and mission, NPO should develop an organizational positioning that allows them to attract and engage volunteers searching for a way of self-expression.
Finally, creating an organizational environment where volunteers can freely share their knowledge and experience is essential.NPO should be open, accessible and adapt to volunteers' contributions (Jaakkola and Alexander, 2014).Building an environment that highlights the importance of teamwork will encourage sharing of experiences and knowledge transfer (Yoo et al., 2022) that will lead volunteers to contribute with new ideas for innovation (Fernandes and Remelhe, 2016).Nonetheless, NPO should consider that such openness to JSTP 33,7 change based on volunteers' contributions may lead to some loss of power by the organization itself (Jaakkola and Alexander, 2014), so each organization needs to ponder their willingness to change.NPO should also identify specific volunteers to set different roles and activities to enhance their value outcomes.Engaged volunteers with knowledge and experience from the work field should participate in strategic planning (Conduit et al., 2019).Work field knowledge can enable customization and expansion of NPO's offerings, leading to a better service to beneficiaries.Since volunteers can promote the focal organization, NPO should identify relevant stakeholders outside their organization and foster partnerships with such stakeholders (Jaakkola and Alexander, 2014).Here, engaged volunteers can also play a key role in acting as a communication channel to impact stakeholders' willingness to partner with the NPO.

Limitations and future research
This study is not without limitations.First, a convenience sample was used, only including volunteers from one European country; hence, generalizations should be taken with caution.Cross-country studies would be welcomed since variables influencing VE may vary based on cultural background.Second, the questionnaire was only available online, meaning that those volunteers without access to the Internet might be underrepresented in our study.Third, although our model explains almost 50% of VE variance, future studies might explore other drivers beyond the ones currently studied, as well as other VE outcomes.Regarding drivers, our approach was based on SDT and SGT, but other theoretical frameworks usually applied in a CE domain, such as the Uses and Gratifications Theory (Katz et al., 1973) could also provide interesting insights.Regarding perceived relatedness, the study focused on connections established with other people within the NPO (i.e. between volunteers); however, prior research (e.g.Millete and Gagn e, 2008) found that interactions between volunteers and beneficiaries can also leverage VE, an alternative path that could be explored in future studies (Nencini et al., 2016).Moreover, other extra-role, engagement behaviors beyond the ones identified by Jaakkola and Alexander (2014), such as helping fellow volunteers by offering advice, expertise and support (van Doorn et al., 2010), could further be examined, as well as impacts of VE on external stakeholders and society at large (O'Brien et al., 2020).Following prior research (e.g.van Schie et al., 2015), our focus was on a generic sense of congruence between volunteers and the NPO; however, we did not specify if this alignment pertains to NPO functioning, culture, rules or cause/mission.Future studies could distinguish between different dimensions of congruence and examine its impacts on VE.It would also be worth studying moderating variables, such as the number of hours spent volunteering, the level of training provided to volunteers or the size and mission of the NPO.Finally, data collection happened at a single point in time.Since engagement can vary over time (Hollebeek et al., 2019), a longitudinal study could provide further insights on whether VE drivers and outcomes are enduring, and on whether a reinforcing "feedback loop" (Brodie et al., 2011) occursthat is if more engaged volunteers feel their basic needs being increasingly fulfilled, thus perceiving more value in their activities (Conduit et al., 2019), which in turn will lead to increased engagement.
Figure 1.Research framework

Table 4 .
Diagonals are the AVE square root of each factor; remaining figures represent correlations Discriminant validity