Tourism and Altruistic Intention: Volunteer Tourism Development and Self-Interested Value

: Volunteer tourism is indisputably an emerging trend in the tourism industry across the globe. Yet, little is known about the altruistic behavior of volunteer travelers. To ﬁll this void, this research explores the convoluted relationships among memorable experience, awareness of problem, social norm, psychological resilience, personal norm, and self-interested value in driving altruistic intention. A ﬁeld survey was conducted with a quantitative approach. The result reveals that psychological resilience and personal norm are direct determinants of altruistic intention while mediating the inﬂuence of awareness of problem and social norm on intention. In addition, memorable experience along with awareness of problem signiﬁcantly induced volunteer travelers’ psychological resilience. Moreover, the test for metric invariance shows that the relationships between psychological resilience, personal norm, and altruistic intention are under the signiﬁcant inﬂuence of volunteer travelers’ self-interested value. Overall, the variance in altruistic intention for volunteer tourism is satisfactorily explained by our suggested theoretical framework.


Introduction
Opportunities for volunteer tourism are more abundant than ever in the global tourism industry [1]. It is undeniable that volunteer tourism is increasing and becoming a popular tourism product/choice in recent years [2,3]. The growth of volunteer tourism has motivated the scholars and the practitioners to conduct a research to explore the behaviors of such tourists and its contributions to the host community [1,2]. For instance, studies have examined related topics, such as volunteer tourism motivations, experiences, attributes, and benefits [3,4]. The previous literatures revealed that volunteer activities include building schools and homes in developing countries, teaching languages to children, saving animals (or improving animal welfare), supporting the community, conserving the environment, and relieving/recovering a post-disaster [5][6][7][8]. As such, volunteer tourism has its altruistic nature while providing meaningful and memorable experiences to tourists [9]. Through various altruistic activities, volunteer tourists get a good understanding of the diverse worlds and the need for help and appreciate what they have [6]. In addition, volunteer travelers can build more confidence, skills, and knowledge while helping others and interacting with new people in local destinations [7,10]. Therefore, volunteer tourism is seen as an important altruistic tourism form that provides novel pro-social experiences for the participants, contributes to the sustainable development of local communities, and requires travelers to inhibit egoistic desires.
Few firmly established theories with altruistic motives such as norm activation theory [11] and value-belief-norm theory [12] indicate that awareness of problem, social norm, and personal norm are decisive constituents when explaining altruistic decision-making process. In addition, psychological resilience and memorable experience are found to significantly influence traveler pro-social intention formation or product choice behavior in extant studies [13][14][15][16][17]. These researchers along with the aforementioned theories stress the importance of memorable tourism experience, awareness of problem, social norm, psychological resilience, and personal norm in clearly understanding individuals' altruistic intention/behavior. However, the empirical effort that examines the possible linkages among these factors has been rarely made in the volunteer tourism context. In addition, the existing theoretical frameworks for altruistic intention/behavior in the literature hardly involve memorable experience and psychological resilience. Furthermore, recent studies in tourism reveal that one's altruistic/pro-social decision formation is under the considerable influence of self-interested value [18][19][20]. Indeed, self-interest and self-enhancement are increasingly becoming of utmost importance in volunteer tourism choices among international travelers [2,7]. Nevertheless, how self-interested value determines the degree of the relationship strength between volunteer tourists' altruistic intention and its proximal predictors has never been uncovered. In other words, a particular moderating role of self-interested value in forming such intention has been unknown.
To fill the void, our study is building a theoretical framework that distinctly illuminates the foundation of altruistic intention of volunteer travelers. Specifically, the aims of this study are to (1) examine the possible interrelations among memorable experience, awareness of problem, social norm, psychological resilience, personal norm, and self-interested value in developing altruistic intention among volunteer travelers, (2) test the mediating role of psychological resilience and personal norm, (3) offer a holistic view by analyzing the relative effect of study variables on altruistic intention generation, and (4) explore how self-interested value moderates the influence of psychological resilience and personal norm on intention for volunteer tourism.

Volunteer Tourism
Volunteer tourism is a mixture of "volunteer" and "tourism", which means tourism that focuses on volunteering [21,22]. In other words, it is a new form of tourism that not only pursues the purpose of enjoying tourism but also devotes some time to volunteering.
However, there is controversy in defining volunteer tourism as it depends on its purpose, timeframe, and elements, etc. [23]. The concepts and definitions of previous studies on volunteer tourism are as follows. According to Liston-Heyes and Daley [22], there is no definite definition of volunteer tourism, but it is commonly said that the definition is provided by Wearing [21]. Wearing [21] defined vacation as volunteering in an organized way, such as helping material poverty in a particular group, restoring a specific environment, or studying social or environmental aspects. In a recent study, Hasanova [24] suggested that a trip includes helping to reduce the material poverty of a social group, restoring a specific environment, or researching social or environmental aspects. Based on the contents of volunteer tourism discussed above, this study defines the concept of volunteer tourism as a new tourism activity that helps social groups in difficult circumstances to get away from their daily lives and to understand and enjoy local culture through exchanges.
Due to altruistic characteristics, volunteer tourism can be seen as a similar context with volunteering. However, the concept of tourism incurs certain costs such as transportation, lodging, and admission to tourist attractions [25]. It also differs in that it is ultimately for personal achievement, rather than volunteer contributions to the community [26]. Thus, volunteer tourism, which includes both leisure and volunteer work, is distinguished from other forms of tourism [27].

Altruistic Intention of Volunteer Travelers
Volunteer tourists are described as volunteers and tourists. Volunteer tourism can be described as an action that is based on altruistic motives, such as contributions to local natural, social and economic aspects, as well as personal motives for experiencing personal growth [28]. In other words, volunteer tourism is driven by altruism and is differentiated from traditional tourism through opportunities for self-discovery, personal growth and valuation [29,30].
Mustonen [31] asserted volunteer tourism contains social elements; altruism, ethical dilemmas, mixture of individuality and sociality and one of them would be the main motivator depends on circumstance. However, generally speaking, it is not easy to distinctly determine whether one's volunteer action is driven by altruistic intention in any one of those motivations. Taking this circumstance into consideration, Brown and Morrison [32], also Brown and Lehto [33], proposed separating volunteer tourists into two groups depending on their motivation, that is, volunteer-minded and vacation-minded tourists. Volunteer-minded tourists are more self-motivated with a greater emphasis on volunteering and often spend time volunteering at tourist destinations. Vacation-minded tourists, on the other hand, are less concerned about volunteering, tend to show more individualism or personality, and are more likely to have pseudo altruism [31][32][33]. Since then, there are many studies which have adopted the concept of volunteer tourist type [34,35].

Memorable Experience and Its Effect
Providing memorable experience is crucial for keeping ahead in the increasingly competitive tourism industry [15,16,36]. In recent years, memorable tourism experience has therefore gained a growing attention from academics and industry practitioners [16,37]. According to Kim et al. [15] and Sthapit and Jiménez-Barreto [16], memorable product/service experience indicates perception that is favorably remembered/recalled after the actual product/service consumption. Consistently, in this study, memorable experience refers to individuals' overall perception of volunteer tourism experience remembered positively. One's memorable experience associated tourism as structured and built in a selective manner [36].
Past studies show that memorable product experience plays an essential role in consumers' post-purchase behaviors [37,38]. Memorable experience not only influences past-directed affective judgments but also triggers loyalty [39,40]. As customers are exposed to product-related stimuli, the uniqueness of the product in entirety would cement itself in the memory stems of the customer, which would, in turn, trigger an internal desire to make future purchases based on the product experience [40]. In the tourism field, Hung et al. [37] found that memorable tourism experience asserts an important role in developing the intention of traveler behavior. More recently, Kim et al. [15] indicated that tourists' memorable tourism experience generates their psychological resilience and well-being, that, in turn, enhanced revisit and word-of-mouth intention. Thus, the following hypothesis is proposed: Hypothesis 1. (H1) Memorable experience has a positive effect on psychological resilience.

Awareness of Problem
Awareness of problem is associated with individuals' apprehension level regarding the diverse facets of social issues (e.g., poverty, war, education, ecological disruption, greenhouse effect, air/soil/water contamination) [12]. Awareness of problem reflects the degree to which individuals are worried about the problems that harm the society and world [11,41]. That is, this concept embraces individuals' favorable/unfavorable attitude toward the issue as well as their mental state toward it [11,41]. In the theoretical approach for the explication of traveler pro-social behavior, Han and Hwang [42] reported that awareness of problem is a significant activator of personal norm. The findings from these studies are in line with the study results of Bamberg et al. [43], showing that awareness of problem is a positive function of moral obligation, and this affects pro-social intention. Awareness of problem is also related to psychological resilience. Kim et al. [15] investigated the behavior of travelers in an airline lounge. The findings demonstrated that travelers' psychological resilience/well-being perception, which is a significant direct influencer of behavioral intention, forms the based cognitive (awareness of need/problem) and affective factors (relaxed/peaceful/refreshed). Thus, the following hypothesis is proposed:

Hypothesis 2. (H2)
Awareness of problem has a positive effect on psychological resilience.

Hypothesis 3. (H3)
Awareness of problem has a positive effect on personal norm.

Social Norm
The social norm has been frequently highlighted in extant studies as a key constituent of volitional process [44,45]. According to Cialdini et al. [46] and Ajzen [47], the term "social norm" is pertinent to the extent to which what individual's behavior should or should not be in a particular social situation. In other words, the main facet of social norm is individual's perception about the particular behavior in which influenced by people whom he/she thinks important. Undoubtedly, this social norm is broadly considered as a critical contributor to increasing individuals' consciousness of moral duty to take an altruistic action in forming behavioral intention [48]. For instance, in the comprehensive and integrative review of determinants of pro-social intention/behavior, Steg and Vlek [49] identified that there is a positive and significant relationship between social norm and personal norm. They described the relationship as a normative process in the formation of pro-social decision. Consistent with their empirical research, Doran and Larsen [50] proved that social norm exercises a significant effect on moral norm in the eco-friendly behavioral context. Given this evidence, the following hypothesis is proposed:

Hypothesis 4. (H4)
Social norm has a positive effect on personal norm.

Psychological Resilience
Due to its significance, researchers and practitioners in psychology and consumer behavior have paid considerable attention to the term "psychological resilience" [51,52]. The concept of psychological resilience refers to travelers' ability to maneuver psychological difficulty in the way of protecting their mental health, improving mental happiness, and increasing the quality of their life [13,15,53]. Psychological resilience, which is pertinent to psychological self-enhancement [40], also reflects patrons' overall life satisfaction, high fulfillment, and positive life attitude [15,54]. In addition, the scope of psychological resilience encompasses individuals' mental health and psychological well-being [13,55]. Indisputably, psychological resilience is the key issue in the tourism marketplace as the number of patrons having trouble with mental health is in more rapid increase than ever [15,53]. Evidence indicates the significant association between psychological resilience and behavioral intention. For instance, in the tourism sector, Hwang and Hyun [56] found that psychological resilience is a vital driver of travelers' behavioral intention. Coherently, in the airline context, Chua et al. [13] showed that travelers' psychological resilience comprising well-being perception make a great contribution triggering their positive behavioral intention for the airline. Given this, the following hypothesis is proposed: Hypothesis 5. (H5) Psychological resilience has a positive effect on altruistic intention.

Personal Norm
Personal norm means one's belief that a traveler's special behavior is ethically proper or improper [57]. Individuals' personal norm is mostly experienced with their sense of moral/ethical duty to conduct a certain action [11,58], which forms their altruistic or socially responsible intention/behaviors [12,57]. While social norms are under the effect of other reference groups, this moral factor is driven by individuals' internal process rather than external process, regulating their behaviors [59]. According to a previous research, the impact of this internal moral factor on individuals' altruistic decision is greater than that of external social factors [42]. Doran and Larsen [50] empirically verified that personal norm has a positive influence on pro-social intention. Han and Hyun [41] also found that this personal norm significantly triggered travelers' altruistic intention to select an ecological product option. Thus, the following hypothesis is developed: Hypothesis 6. (H6) Personal norm has a positive effect on altruistic intention.

Self-Interested Value and Its Role
Value refers to how consumers consider the product/service value based on the trade-off of what customers sacrifice and what they receive from a transaction [60]. Oh [61] and Lee et al. [62] noted that value judgments in marketing contexts are a highly subjective, cognitive, and plausibly emotional evaluation of a consumption experience, whereby the evaluation is relativistic to the dynamic comparison processes in accordance to the designated consumption situation. All things considered, the core aspect of individuals' value perception comprises their self-interest. In those studies, self-interested value refers to one's cognitive appraisal derived from the comparison between what they give up (e.g., time and effort) and what they obtain (e.g., benefits) through volunteer tourism.
Anti-altruistic actions frequently imply behaving according to egoistic interests, whereas most altruistic activities require individuals to wholly restrain their self-interest goal/desire for benefiting the society [18,48]. Nonetheless, fulfilling individuals' self-interest desire is also regarded to be of significance in the altruistic behavior literature [7,19,20]. Indeed, researchers agree that centering solely on one's pro-social/moral concern and awareness is insufficient to cause them to practice altruistic behaviors [18]. Individuals' altruistic decision/behaviors can be maximized when they pursue both pro-social and self-interest goals [19,20,63]. In the situation where seeking personal interests is completely inhibited, volunteers are less motivated to behave in an altruistic manner [7]. According to Han et al. [64], individuals' self-interest value/perceive benefits significantly affect the formation of behavioral intention as the moderators in the international tourism context. Their finding is consistent with Gremler et al. [65] who asserted a significant moderating effect of self-interest benefits on customer decision formation. Thus, the following hypotheses are developed: Hypothesis 7. (H7) Self-interested value acts as a significant moderator between psychological resilience and altruistic intention.

Hypothesis 8. (H8)
Self-interested value acts as a significant moderator between personal norm and altruistic intention.

Measurement Items and Survey Questionaire
We adopted the validated measurement items that are widely used from the extant consumer behavior, psychology, and tourism literature [2,13,66,67]. In addition, we modified the measures to be suitable in the volunteer tourism situation. All variables are measured with several items under a 7-point Likert scale. Memorable experiences were assessed with a 3-item (e.g., "I had countless memorable experiences with this volunteer activity"), while awareness of problem are evaluated with a 3-item (e.g., "I have increased my awareness of helping others by participating in this volunteer tourism program"). A 3-item and a 4-item were used to measure social norm (e.g., "People whose opinions I value prefer that I participate in a volunteer tourism program") and psychological resilience (e.g., "In most aspects, my life has become close to my ideal after participating in this volunteer tourism"), respectively.
Personal norm was assessed with a 3-item (e.g., "I feel a moral obligation to take altruistic action through a volunteer tourism program"), while self-interested value was measured with a 4-item (e.g., "Comparing what I have given up with that which I have received, the overall experience of this volunteer tourism in terms of satisfying my needs and wants is valuable"). Lastly, altruistic intention is assessed by a 3-item (e.g., "I will exert an effort to participate again in a volunteer tourism program in the near future"). These measurement items of each study construct were included in the survey questionnaire. A few tourism academics pre-tested the questionnaire, which was then improved based on their feedback. Moreover, two volunteer tourism experts reviewed and confirmed the set of questions.

Data Collection and Demographic Profile of Samples
Data collection was conducted at the Good News Corps Festival, which celebrates the successful completion of individuals' overseas volunteer tourism activities. The data collection was done in Spring 2019. The participants of the festival are mostly volunteer tourists who participated in the one year-long international volunteer tourism program and their family members. The surveyors delivered the questionnaires to the participants of the volunteer tourism program during the festival. In agreement with the survey participation, a brief description of the study and its purposes were explained to the survey participants. They filled the questionnaire based on their latest volunteer tourism experience. The filled questionnaire was returned onsite and then was checked for completeness by the surveyors. A small gift was given to all participants as an expression of gratitude. A total of 302 usable cases were obtained.
Among the 302 participants, 57.3% were men (n = 173), and 42.7% were women (n = 129). The participants were 23.75 years old on average and their age range was between 20 to 37 years old. The respondents' income was questioned. Approximately 54.4% stated income in the range of $25,000-$54,999; after that, under $25,000 (29.6%); in the range of $55,000-$84,999 (12.0%), and $85,000 or higher (4.0%). Regarding education level, a majority of respondents held a bachelor's degree or were university students (78.1%), followed by 13.9% with a 2-year degree/community college degree, 4.3% were graduate degree holders, and 3.6% had a high school diploma or less. With regards to the frequency of international volunteer tourism, most respondents answered that it was their first volunteer tourism experience (83.8%), followed by twice (6.6%), 4 times or more (6.3%), and 3 times (3.3%).

Measurement Model and Data Quality Assessment
A confirmatory factor analysis was performed to create the measurement model. Table 1 shows the model includes the acceptable level of fit to the data: χ 2 = 485.629, degree of freedom (df ) = 209, p < 0.001, χ 2 /df = 2.324, root mean square error of approximation (RMSEA) = 0.066, comparative fix index (CFI) = 0.946, incremental fit index (IFI) = 0.946, Tucker-Lewis index (TLI) = 0.934. All measurement items for each latent factor were significantly loaded (p < 0.01). The assessment of composite reliability (CR) demonstrates that all values were above the threshold 0.60 [68] (memorable experience = 0.892; awareness of problem = 0.851; social norm = 0.929; psychological resilience = 0.866; personal norm = 0.898; self-interested value = 0.812; altruistic intention = 0.950), which generates the internal consistency of the measures. The outcome of average extracted values (AVE) shows that all figures were above the suggested threshold of 0.50 [68] (memorable experience = 0.734; awareness of problem = 0.657; social norm = 0.814; psychological resilience = 0.619; personal norm = 0.747; self-interested value = 0.520; altruistic intention = 0.865). In addition, as Table 1 shows, these figures were bigger than the between-construct correlations (squared), which demonstrate evidence of discriminant validity.

Hypotheses Testing and Strucural Analysis
The detailed results of the structural equation model are presented in the below Table 2 and Additionally, about 28.8% of the total variance in altruistic intention was explained by its variables. The proposed impacts of memorable experience and awareness of problem are evaluated. The impact of memorable experience (β = 0.264, p < 0.01) and awareness of problem (β = 0.543, p < 0.01) are a positive and significant influence on psychological resilience, respectively. Thus, the result supported hypotheses 1 and 2. In regards to hypotheses 3 and 4, our result showed that awareness of problem (β = 0.492, p < 0.01) and social norm (β = 0.307, p < 0.01) include a positive and significant impact on personal norm. This result supported hypotheses 3 and 4. The proposed effect of psychological resilience and personal norm on altruistic intention was measured. The outcome showed that both psychological resilience (β = 0.211, p < 0.01) and personal norm (β = 0.413, p < 0.01) had a positive and significant effect on altruistic intention. Hence, we support hypotheses 5 and 6.
We investigated the indirect and total effect of research variables. The outcome revealed that awareness of problem had a positive and significant indirect effect on altruistic intention (β = 0.318, p < 0.01). Moreover, the indirect effect of social norm on altruistic intention was significant (β = 0.127, p < 0.05). These results suggest that psychological resilience and personal norm acted as a significant mediator between awareness of problem and social norm on altruistic intention. Consequently, the total effect of research constructs was tested. Personal norm had the strongest total impact on altruistic intention (β = 0.413, p < 0.01), after that, awareness of problem (β = 0.318, p < 0.01), psychological resilience (β = 0.211, p < 0.01), social norm (β = 0.127, p < 0.05), and memorable experience (β = 0.056, p > 0.05).  We investigated the indirect and total effect of research variables. The outcome revealed that awareness of problem had a positive and significant indirect effect on altruistic intention (β = 0.318, p < 0.01). Moreover, the indirect effect of social norm on altruistic intention was significant (β = 0.127, p < 0.05). These results suggest that psychological resilience and personal norm acted as a significant mediator between awareness of problem and social norm on altruistic intention. Consequently, the

Assessment of Moderating Effect and Invariance Test
For the assessment of the hypothesized moderating effect, an invariance test was obtained. We divided the respondents into the high group of self-interested value and the low group of self-interested value by using a K-means cluster analysis. There were 195 cases in high group while 107 cases in low group. A baseline model comprising both high and low self-interested value groups was then built. Table 3 and Figure 1 demonstrate the model contained a satisfactory level of fit to the data (χ 2 = 615.205, df = 299, p < 0.001, χ 2 /df = 2.058, RMSEA = 0.059, CFI = 0.919, IFI = 0.919, TLI = 0.907). We compared this baseline model to the nested models in which a specific path is restricted in an equal manner. The outcome of the invariance model assessment is shown in Table 3. Our finding from the chi-square test showed that the linkage from psychological resilience to altruistic intention significantly differs between high and low groups of self-interested value (∆χ 2 (1) = 9.344, p < 0.01). Therefore, hypothesis 7 was supported. Our result also showed that the relationship between personal norm and altruistic intention was significantly different between the two groups (∆χ 2 (1) = 4.851, p < 0.05). Accordingly, hypothesis 8 was supported. Overall, our result demonstrated that self-interested value acted as an important moderating part within the projected conceptual framework.

Discussion
In the proposed framework, memorable experience was positively associated with psychological resilience, and this relationship significantly contributed to fostering altruistic intention. Given this, a strategy that efficiently elicits such predictors needs to be the volunteer tourism management direction. It is crucial for volunteer tourism practitioners to take note of developing more experiential activities as part of the quality enhancement of the volunteer tourism program. To do so, the volunteer tourism program should be more specifically designed to offering memorable and meaningful moments to the participant where some psychological benefits (e.g., self-fulfillment, feeling of pride, life satisfaction) can be generated when helping the local community. Such moments can be also documented via videos/pictures and shared with the volunteer tourism program participants. In addition, the volunteer tourism program should offer more opportunities for volunteers to interact with the locals and their culture and history. Volunteer tourists can have new and meaningful experiences which broaden their horizons and change their views of the world through such interactions. These efforts would result in increased memorable experience and psychological resilience among volunteer tourists, which eventually boost altruistic intention.
Findings of our research demonstrate the important moderating part of self-interested value on the association between psychological resilience and altruistic intention. Especially, relationship strength was significantly stronger in the high group than in the low group (high group: β = 0.318, p < 0.01 vs. low group: β = −0.025, p > 0.05). In other words, at the same level of psychological resilience, volunteer travelers who feel stronger self-interested value tend to feel altruistic intention to volunteer tourism than those who feel lower self-interested value. This empirical result includes crucial theoretical and practical implications. Theoretically, the impact of self-interested value is hardly tested in the volunteer tourism context. Our research shed light on the vital function of self-interested value in clearly explicating volunteer tourists' behaviors. Utilizing this variable as a moderator is therefore important in expanding any theory or conceptual framework for volunteer tourism. Practically, volunteer tourism practitioners should not ignore offering high self-interest value to volunteers for the effective elicitation of their altruistic intention/behavior.
The results of the invariance test provides evidence that self-interested value moderates the linkage from personal norm to altruistic intention. Specifically, the relationship strength was significantly stronger in the low party as compared to the high party (high party: β = 0.300, p < 0.01 vs. low party: β = 0.611, p < 0.01). Such results imply at the similar level of personal norm, volunteer tourists who perceive lower self-interested value are more likely to form altruistic intention to volunteer tourism than those who perceive higher value. This contradicting result as compared to the moderating part of self-interested value in psychological resilience and intention relationship can be due to the characteristics of the concept of personal norm. Researchers generally agree that personal norm is a key pro-social concept [57][58][59]. Indeed, many theories with pro-social motives [11,12] utilized personal norm as a major concept in explicating socially responsible intention/behavior. For that reason, volunteer tourists' personal norm is more strongly activated in pro-social behavior when they consider less the possible self-interests or benefits that are barely pro-social.
Our structural analysis result reveals that awareness of problem, social norm, and personal norm were crucial variables contributing to building altruistic intention. For researchers, our result provides an important theorization that increasing volunteer tourists' perceived awareness about the need for help in volunteer tourism destinations and enhancing their social norm can trigger their moral norm that ultimately induces altruistic intention for volunteer tourism. Volunteer tourism practitioners thus need to inform volunteers of the diverse forms of problems (e.g., social, environmental, educational, criminal, ecological, deficient/necessitous) in the volunteer tourism destinations through diverse communication channels of media (e.g., Internet, media, magazine, newspaper, SNS). This effort would eventually enhance volunteer tourists' perceived level of awareness, social pressure, and consciousness of moral duty to bring an altruistic action.
Findings of recent studies indicate that the impact of cognitive factors on pro-social intention is often maximized by the mediating influence of moral obligation and psychological resilience [15,42,50]. Consistently, our result reveals that personal norm and psychological resilience play an essential role of intensifier of volunteer travelers' altruistic intention. Our finding provides volunteer tourism practitioners and researchers significant insight: in order to elicit the maximum influence of awareness of problem and social norm on volunteer travelers' altruistic decision, boosting personal norm and psychological resilience is necessary. Based on the intricate theoretical mediating mechanism found in this study, dealing with such mediators for the efficient enhancement of altruistic intention among volunteer tourists is essential.

Conclusions
Indisputably, inducing individuals' altruistic tourism behaviors is one of the essential issues in the global volunteer tourism sector. Yet, what factors trigger altruistic behaviors and how altruistic decisions form have not been distinctly uncovered. This study filled this void that not only contributes to the current knowledge about the volunteer tourism but also provide a wider range of understanding of altruistic behavior. The proposed theoretical framework was entirely supported. Memorable experience, awareness of problem, social norm, psychological resilience, personal norm, and self-interested value were clearly found as critical determinants of volunteer tourists' altruistic intention. This outcome may assist volunteer tourism practitioners in establishing useful tactics to drive volunteer tourists' altruistic decisions/behaviors by using pro-social and self-interest motives as tools. The theoretical base associated with volunteer tourism and volunteer tourists' altruistic behaviors are still in the infant stage. In this aspect, the present study includes strong value and originality. This study can help subsequent research about volunteer tourism and altruistic/pro-social tourism behaviors.
The present research included certain limitations that provide future study opportunities. Firstly, travelers' decision formation and behaviors can differ based on personality traits (e.g., extroversion, agreeableness, conscientiousness, neuroticism, openness to experience) [69,70]. Similarly, it is conceivable that volunteer tourists' behaviors can be different across personality traits. Nevertheless, this study did not consider the possible influence of personality traits. Future research could integrate the effect of personality traits based on our suggested framework. Secondly, according to Sirgy [71], hedonic factors, which were not involved in our proposed model, are the crucial elements when explicating tourists' behaviors. Future research should broaden the proposed model with an integration of hedonic factors for a more comprehensive understanding of volunteer tourists' behaviors.

Conflicts of Interest:
The authors declare no conflict of interest.