Impacts of Personal Characteristics on User Trust in Conversational Recommender Systems

Conversational recommender systems (CRSs) aim to mimic a human advisor to assist users in looking for recommendations in a multi-turn dialogue via text or voice [17, 29, 74, 75], and have been applied in several domains, such as movies [10], music [11, 30], and e-commerce [75]. Unlike single-shot traditional recommender systems [63], CRSs allow users to interact with the system in a multi-turn conversation, enabling the system to incrementally refine the user preference model to generate more satisfying recommendations [10, 34]. Such systems can support mixed-initiative interaction by combining both user-initiative (i.e., users actively tell the system what they want) and system-initiative (i.e., the system proactively offers suggestions to users during the recommendation process) interactions, which is regarded as a more flexible interaction strategy in human-computer interaction (HCI) [3]. Several recent studies on CRSs have demonstrated that such systems enable more natural interactions between the user and the system, which can better enhance user experience with recommender systems [11, 29, 30, 55].

With increased interest in CRSs, recommender system researchers have been focusing on improving CRS efficiency (i.e., reducing the number of dialogue turns) and effectiveness (i.e., improving the recommendation quality) [22, 29, 75]. Although conversational system design is a trending topic within the HCI community, few studies have investigated conversational interaction designs for recommender systems [11, 29, 30, 60]. For instance, one study compared two critiquing-based conversational music recommenders that employed different initiative strategies [30], and found that the user-initiative CRS gives users more control to tune recommendations on their own, whereas the mixed-initiative CRS guides users to discover more diverse recommendations. Another recent study demonstrated the ability of a CRS to promote user exploration activities [11], and suggested that the mixed-initiative CRS enhances user exploration by allowing users to control the exploration direction on their own as well as guiding them to explore something different. While existing studies have demonstrated several advantages of CRSs, work on the critical factor of user trust, which strongly determines users’ intention to adopt CRSs in real-world situations, is limited. Thus, this study aims to investigate the factors that may affect user trust in CRSs.

Trust is an important factor in both human-human and human-computer relationships [21, 44, 46], which has been studied for a long period. Trust is defined in various ways in the existing HCI literature [45, 50, 73], but a common theme is that trust can be regarded as a behavioral intention (e.g., intention to use) or “trusting intention” [50]. Studies have suggested three types of factors that can influence trust: user-related, system-related, and context-related factors. These three types of factors respectively correspond to the three layers of trust model proposed by Hoff and Bashir [26]: Dispositional trust refers to the user's general tendency to trust systems, which may arise from individual characteristics such as personality (user-related); learned trust represents the user's evaluations of a system's trustworthiness drawn from past interactions (system-related); situational trust is based on the context of the user-system interaction, such as the complexity of the performed task and user workload (context-related). Motivated by the three-layered trust model [26], we are interested in examining these three types of factors (user-related, system-related and context-related) that may influence user trust in CRSs.

Trust-related issues have also gained a lot of attention in recommender systems (RSs), because user trust highly influences users’ willingness to use a system and follow its recommendations in their decision-making process [38, 40, 57, 72]. User trust in a technological artifact (e.g., recommender system) is often based on competence (i.e., the system's ability to assist users in a specific task), benevolence (i.e., the system's qualities such as security and reputation), and integrity (i.e., the system's reliability and honesty) [50]. Studies on RSs have demonstrated that users’ perceived competence of the system positively influences their trust in the system [12, 41]. For example, the accuracy and diversity of recommendation lists tend to improve user trust and increase customer purchases in the e-commerce domain [58]. Moreover, the organization-based recommendation interface was demonstrated to reduce user effort in the decision-making process, sustain user trust, and increase users’ intention to use the system [12]. Recommendations accompanied by explanations that provide information to assist users in making judgments on the recommended item have also been shown to increase user trust and decision confidence [12, 70].

Literature on user trust in RSs has mostly focused on the aspect of recommendations [41, 41, 58], whereas, to the best of our knowledge, user trust in the context of conversational recommendations has rarely been investigated. In CRSs, the conversational interaction between users and the system usually mimics human communication, suggesting that user trust toward the system is similar to trust in interpersonal relationships. Thus, to improve trust, the system should be both reliable in performing the requested tasks and predictable in interactions (i.e., behaving as expected by the user) [62]. However, individual users may have their own expectations of interaction strategies (e.g., preference for user-initiative or mixed-initiative) depending on their individual characteristics, which may influence their trust in the system. To facilitate the design of trustworthy CRSs that can serve individual users’ needs, our work focuses on investigating the impact of personal characteristics on user trust in CRSs that employ different initiative strategies.

Because previous HCI and RS studies have indicated that user trust in the human-system relationship depends on individual characteristics [16, 26, 76], we believe that user trust in CRSs may also be influenced by users’ personal characteristics. The literature suggests that three personal characteristics, namely personality traits, trust propensity and domain knowledge, are likely to affect user trust in conversational recommenders.

Personality Traits. Personality is defined as individual differences in one's enduring way of thinking, feeling, and behaving [37, 48]. The Big-Five personality model, which comprises five traits – openness to experience (openness), conscientiousness, extroversion, agreeableness, and neuroticism – is widely used to assess user personality [48]. Studies have reported the impacts of personality traits on trust in interpersonal relationships [21], demonstrating that openness and conscientiousness affect trust in both friends and strangers, and agreeableness affects trust in strangers. Personality traits also influence user trust in the human-machine collaboration [16, 76]; for example, people who are more agreeable and conscientious are more likely to trust automation in decision-making [16]. Thus, we speculate that personality traits (such as agreeableness and conscientiousness) can also influence user trust toward system guidance in CRSs.

Trust Propensity. Trust propensity is defined as the general tendency to trust others [18, 64] and is viewed as a dynamic individual difference that may be affected by personality type as well as situational factors (e.g., cultural background) [47]. Trust literature has shown that a user's trust propensity influences the formation of trust toward specific technological systems [49, 50]. When deciding whether to trust a system, users tend to look for cues that signify the system's trustworthiness; however, the perception of the signals is affected by their trust propensity [45]. Thus, we seek to determine whether this characteristic will impact user trust in CRSs.

Domain Knowledge. Domain knowledge refers to a person's expert knowledge in a specific field. HCI research has demonstrated that users’ domain knowledge can influence their interaction behaviors and preferred interaction strategies [56]. In recommender systems, domain experts prefer more control during the decision-making process [38], whereas domain novices tend to perceive recommendations without too much control to be more helpful. Moreover, users’ reliance on decision support systems is related to their domain knowledge; for example, users with little or no specialized domain knowledge are likely to rely on the system's suggestions [8]. Thus, we believe that domain knowledge may influence the way users prefer to interact with CRSs (e.g., preference for user-initiative or mixed-initiative), hence affecting user trust.

Based on Hoff and Bashir's three-layered trust model [26], we investigated how user-related factors (personal characteristics) interact with both a system-related factor (initiative strategy) and a context-related factor (task complexity) to influence user trust in CRSs. We deployed two text-based prototype conversational music recommenders that employ different initiative strategies (user-initiative and mixed-initiative) [11], and designed two user tasks of varying complexity in the recommendation domain. Thus, we designed a 2 (User-Initiative vs. Mixed-Initiative) × 2 (Simple Task vs. Complex Task) online between-subjects user study, in which participants were randomly assigned to one of the four experimental conditions (see Figure 2). Below we present two experimental manipulations.

Figure 2 shows the interfaces of two text-based conversational music recommenders employing different initiative strategies. The left side of the figure shows the interface of the User-Initiative system, and the right side of the figure shows the interface of the Mixed-Initiative system. The middle shows two user tasks, simple task and complex task in our 2 ?? 2 between-subjects study.

3.1.1 Conversational Recommenders. We used two variants of text-based conversational music recommenders that employ different initiative strategies to support users in looking for music recommendations [11]:

• User-Initiative System: This system, which performs reactive system behavior, only responds when users initiate requests during the conversation. In this system, users can post feedback to refine the current recommended item or ask for songs based on music-related attributes (e.g., genres, tempo, and danceability). For example, a user can tune a recommendation by typing “I want higher tempo.”
  
• Mixed-Initiative System: This system supports both user-initiative and system-initiative interactions. Specifically, in addition to reactively responding to users’ requests, the system can proactively provide suggestions (e.g., “Compared with the last played song, do you like the song of lower tempo?”) to facilitate users’ music discovery during the recommendation process. As suggested by a study of chatbot proactivity [60], our system offers suggestions to users when they make an explicit request (i.e., by clicking the “Let bot suggest” button; Figure 2) or when the system identifies a good time to offer suggestions.²
  

Although conversational systems can employ three types of initiative strategies, namely user-initiative, system-initiative, and mixed-initiative strategies, we did not employ a purely system-initiative strategy in our study because this design relies on a “system asks, user responds” conversation paradigm [75], which can restrict user interaction, reduce flexibility, and make users feel passive [29, 36].

Figure 2 shows the user interfaces of the two conversational music recommenders, and the dialogue windows show the conversation between the user and the system. Each recommended song is displayed on a card using which the user can control music playback, along with a set of buttons under the card for the user to give feedback. Specifically, the user can click the “Like” button to add the current song into their playlist where they can rate the song, and the “Next” button to skip the current song. In the Mixed-Initiative system, the user can click the “Let bot suggest” button to trigger the system's suggestion based on the currently recommended song. Additionally, the user can send a message in natural language about the music genre, audio feature, or artist to provide feedback on the currently recommended song and accordingly refine the recommendation. We used a popular natural language understanding platform, DialogFlow,³ and a widely used online music service, Spotify API,⁴ to develop our conversational music recommenders. For the generation of the system-initiative suggestions, we employed the progressive system-suggested critiquing technique designed by Cai et al. [11], which considers the user's song preferences as well as incremental feedback captured from past interactions.

We recruited participants from Prolific,⁵ a popular platform for academic surveys [59]. To ensure experiment quality, we pre-screened users in Prolific using the following criteria: (1) participants should be fluent in English; (2) they must have more than 100 previous submissions; (3) their approval rate should be greater than 95%. The experiment took 25 minutes to complete on average. We compensated each participant £2.40 on successfully completing the experiment. The Research Ethics Committee (REC) of the authors’ university approved this study.

In total, 194 users participated in our study. We removed the responses of 23 participants because of their excessively long experiment completion time (outliers). We excluded the responses of another 23 participants who failed the attention check questions.⁶ Thus, the remaining responses of 148 participants were included in the analyses [User-Initiative: Simple Task (32), Complex Task (35); Mixed-Initiative: Simple Task (45), Complex Task (36); Gender: female (70), male (75), other (3); Age: 19-25 (69), 26-30 (27), 31-35 (25), 36-40 (10), 41-50 (11), > 50 (6)]. Participants were mainly from the United Kingdom (32), the United States (32), Portugal (18), Poland (12), and Italy (9).

Participants had to accept a general data protection regulation consent form before they signed into our system using their Spotify accounts. After reading the user study instructions, participants were asked to fill out a pre-study questionnaire, which included demographic questions and questions for measuring their personal characteristics (see Section 3.4). To ensure that participants understood the study task and how to use the conversational recommender, they were given a tutorial of interacting with the assigned conversational music recommender, followed by two minutes to try the system. After completing the tutorial, participants were asked to complete a randomly assigned task (Simple Task or Complex Task as described in Section 3.1.2). After finishing the task, participants were asked to fill out a post-study questionnaire regarding their trust-related perception of the conversational music recommender (see Section 3.5).

In the pre-study questionnaire, we used a short personality test, the Ten Item Personality Inventory (TIPI) [23], to assess participants’ Big-Five personality traits: openness to experience, conscientiousness, extroversion, agreeableness, and neuroticism. Each personality trait is assessed by two questions in the TIPI, and the personality value for each trait is the average of the scores on the two questions. To measure participants’ trust propensity, we adopted two statements developed by Lee and Turban [45]: “I tend to trust the recommender, even though having little knowledge of it.” and “Trusting someone or something is difficult.” Because our system was built for the music domain, we used the nine statements from the “Active Musical Engagement” facet of Goldsmiths Musical Sophistication Index [53] to assess participants’ musical sophistication as their domain knowledge. All statements were rated on a 7-point Likert scale from 1 (strongly disagree) to 7 (strongly agree). In Table 1, we briefly introduce each measured personal characteristic.

Table 2 shows the descriptive statistics of our participants’ personal characteristics (PCs). The scored values are centered between 3 and 5 for almost all PCs, and the standard deviations are comparable across all PCs. Table 3 shows Pearson's correlations between these PCs; these correlations (e.g., trust propensity is positively related to extroversion and agreeableness) are generally consistent with the results of previous literature [21, 24, 33].

In the post-study questionnaire, we measured users’ trust-related perception of the conversational music recommender in two main dimensions: Competence Perception and User Trust. Competence Perception refers to how users perceive the system's competence in assisting them in performing tasks, which contains the following three constructs derived from prior works [13, 39, 71]:

• Perceived Recommendation Quality: This construct measures the system's ability to provide good recommendations to help users make decisions or support their exploration. Users may judge the quality of recommendations in terms of several aspects, e.g., accuracy, novelty, and serendipity [13, 39]. A previous study showed that users’ perceived recommendation quality influences their perceived usefulness of the system in helping them accomplish tasks, which consequently impacts user trust toward the system [13]. Thus, we considered this construct and measured it using questions from ResQue [13], a widely used user-centric evaluation framework for recommender systems.
  
• Perceived Conversational Interaction: This construct measures the system's ability to effectively communicate with users to perform tasks during the interaction. Several aspects of conversational interaction are deemed crucial to CRSs [31], which include understandability, perceived control, interaction adequacy (i.e., ability to elicit and refine preferences [13]), and naturalness of the dialogue interaction. Because communication is the primary way people develop trust within interpersonal relationships [19], we hypothesize that users’ experience with conversational interaction will also influence the formation of user trust in the system. We measured this construct by adopting questions mainly from an evaluation framework for conversational agents [71].
  
• Perceived Effort: This construct measures users’ perceived difficulty or ease in using the system for completing their tasks, which can reflect the effectiveness of the system in supporting users to accomplish tasks. When users perceive high effort in using the system to complete tasks, they may feel frustrated and show less trust [12, 13]. We used questions in ResQue [13] to measure this construct.
  

The User Trust dimension directly measures user trust in the CRS based on two constructs, each measured using one question item: Perceived Trust assesses users’ overall feelings of trust toward the conversational recommender, and Intention to Use measures users’ willingness to use the system in the future.

We assessed the validity of our constructs as measured by the question items (19 items in the initial questionnaire) by conducting confirmatory factor analysis (CFA) with R library Lavvan.⁷ In CFA, the items within the same scale are represented by a latent factor, where the loading of each item denotes how strongly that item is associated with the corresponding factor. We iteratively removed 5 items with low loadings (<0.50) or high cross-loadings, leaving behind 14 items in total (Table 4). All items were assessed by 7-point Likert scale from 1 (strongly disagree) to 7 (strongly agree). Each factor had good internal consistency (Cronbach's α > 0.80), composite reliability (CR > 0.80), and convergent validity [Average Variance Extracted (AVE) > 0.50] [1], and the loading of each item exceeded the acceptable level of 0.50, with an overall good model fit [27]: χ²(51) = 86.283, p <.001; Root Mean Square Error of Approximation (RMSEA) = 0.068, Comparative Fit Index (CFI) = 0.967, Turker-Lewis Index (TLI) = 0.957.

Figure 3 illustrates the results of the structural equation modeling (SEM) analysis, showing all significant paths in our model. The SEM model had overall good model fit indices: χ²(123) = 182.312, p <.001; RMSEA = 0.057, CFI = 0.956, TLI = 0.947, which meet the recommended SEM fit standard.⁸

Figure 3 shows the results of structural equation modeling. The results indicate that two personality traits, conscientiousness and extroversion, influenced User Trust via Competence Perception, and trust propensity and musical sophistication directly affected User Trust. The numbers on the arrows represent the ?? coefficient and standard error (in parentheses) of the effect.

In the resulting model, the paths between the perception constructs (inside black rectangles) show how users’ perceptions of the system's competence influenced their trust in the CRS. Specifically, the significant paths (Perceived Recommendation Quality → Perceived Trust and Intention to Use; Perceived Conversational Interaction → Perceived Trust and Intention to Use) justify the positive effects of users’ competence perception of the CRS on their trust in the CRS. Furthermore, the path coefficients indicate that Perceived Trust was affected more by Perceived Conversational Interaction (coefficient = 0.695) than Perceived Recommendation Quality (coefficient = 0.235). Our model also verifies the positive effect of Perceived Trust on Intention to Use [61]. Additionally, we observed an interesting path (Perceived Conversational Interaction → Perceived Effort → Perceived Recommendation Quality), showing that users’ perceptions of conversational interaction positively influenced their perceptions of the recommendation quality, which were mediated by their perceived effort. These effects highlight the importance of considering Perceived Conversational Interaction for inspiring user trust in CRSs.

Moreover, our SEM model shows how personal characteristics influence the constructs of Competence Perception and User Trust. The results indicate that two personality traits (conscientiousness and extroversion) influenced User Trust via Competence Perception, whereas trust propensity and domain knowledge (musical sophistication) directly affected User Trust in the CRS.

• Conscientiousness. The trait conscientiousness positively influenced users’ perceptions of conversational interaction: users with higher conscientiousness tended to have a better perception of their interaction with the conversational recommender.
  
• Extroversion. The trait extroversion was positively related to users’ perceived recommendation quality. Users with higher extroversion tended to perceive higher system competence in recommending satisfying songs. One possible explanation is that compared with introverted users, extroverted users (who are more outgoing and vigorous [33]) are more willing to take risks and try listening to different music during the interaction, hence improving their perceptions of recommendations.
  
• Trust Propensity. Trust propensity positively affected users’ perceptions of the conversational interaction and their intention to use. Namely, users who are more willing to trust others tended to enjoy the conversational interaction with the CRS and have a higher intention to use it again. People with a higher trust propensity (who tend to believe others are sincere and have good intentions [18]) may be more cooperative [28] with the system during the conversation, resulting in a more positive conversational experience.
  
• Musical Sophistication. Regarding the influence of domain knowledge, we found that musical sophistication positively influenced users’ intention to use the CRS, suggesting that users with higher musical sophistication are more likely to use the conversational recommender in the future.
  

In addition to the user-related factors (personal characteristics), we investigated whether the system-related factor (initiative strategy) and the context-related factor (task complexity) directly influenced user trust in the model. Among these factors, task complexity negatively affected users’ perceived conversation interaction (p <.05), which may be attributed to the increased user effort required to perform a complex task.

As inspired by previous studies [38, 54], individual users may have different perceptions of the two conversational recommenders (User-Initiative and Mixed-Initiative systems), and may show different attitudes when performing the two user tasks (Simple Task and Complex Task), which may influence their formation of trust in the CRS. Therefore, we investigated how the user-related factors (personal characteristics) interact with the system-related factor (initiative strategy) and the context-related factor (task complexity) to influence user trust in the CRS. Specifically, we used linear regression models to process the mix of numerical and categorical independent variables, namely personal characteristics, initiative strategy and task complexity as the independent variables, and the five trust-related perception constructs (Table 4) as the dependent variables. Table 5 presents the results of the regression models that show how users’ trust-related perception is influenced by personal characteristics, initiative strategy, and task complexity, revealing their interaction effects (represented by interaction terms in the model). We report coefficients, standard errors, p-values, R² and adjusted R² values.

Figure 4 illustrates the interaction effects between personal characteristics and initiative strategy on users’ trust-related perception constructs. Subfigures (a-c) show that users with higher Conscientiousness tended to have a better perception and showed more trust in the Mixed-Initiative system. Subfigure (d) shows that users with higher Musical Sophistication tended to perceive higher recommendation quality from the User-Initiative system.

4.2.3 Interaction Effects between Personal Characteristics and Task Complexity. From Table 5, significant interaction effects were detected between task complexity and three personal characteristics, conscientiousness, trust propensity, and musical sophistication:

• Conscientiousness. We found a significant interaction effect between the trait conscientiousness and task complexity on users’ perceived recommendation quality. As visualized in Figure 5(a), the positive effect of conscientiousness on perceived recommendation quality was observed when users perform the Simple Task (r = 0.32, p <.01, 95% CI: [0.10, 0.51]), but no relationship was found for the Complex Task. Together with the results in Figure 4(a), a crossover interaction effect was observed between conscientiousness and initiative strategy, suggesting that when users perform the Complex Task, their conscientiousness levels may differently influence their perceived recommendation quality, depending on the system's initiative strategy (user-initiative or mixed-initiative).
  
• Trust Propensity. Task complexity influenced the effects of trust propensity on users’ perceived effort and intention to use the conversational recommender. Specifically, users with higher trust propensity levels tended to feel less effort using the conversational recommender to perform the Complex Task (r = -0.34, p <.01, 95% CI: [-0.53, -0.12]), but the correlation between them was not obvious regarding the Simple Task [see Figure 5(b) ], probably due to the intrinsically lower user effort required for the Simple Task. Moreover, trust propensity positively influenced users’ intention to use the conversational recommender (also shown in Figure 3), and Figure 5(c) shows that the positive effect was stronger when users performed the Complex Task (r = 0.32, p <.01, 95% CI: [0.09, 0.52]) than the Simple Task (r = 0.27, p <.05, 95% CI: [0.04, 0.46]).
  
• Musical Sophistication. A significant interaction effect was detected between musical sophistication and task complexity on users’ perceived recommendation quality. As shown in Figure 5(d), when performing the Simple Task, users with higher musical sophistication tended to have a more positive perception of recommendations than users with lower musical sophistication (r = 0.34, p <.01, 95% CI: [0.12, 0.52]), which could be due to the higher skill levels of music professionals for tuning recommendations to find songs that suit their tastes.
  

Figure 5 illustrates the interaction effects between personal characteristics and task complexity on users’ trust-related perception constructs. Subfigure (a) shows that Conscientiousness showed a positive effect on the users’ perceived recommendation quality for the Simple Task. Subfigures (b and c) show that the effects of Trust Propensity on users’ trust-related perception were stronger for the Complex Task. Subfigure (d) shows that users with higher Musical Sophistication tended to have a better perception of recommendations for the Simple Task.

Table 6 summarizes the effects of the three personal characteristics on user trust toward the conversational music recommenders and their interaction effects with the initiative strategy (User-Initiative and Mixed-Initiative) and with the task complexity (Simple Task and Complex Task). Overall, trust propensity and musical sophistication directly influenced users’ intention to use, and conscientiousness interacted with the initiative strategy to influence users’ perceived trust in the CRS.

Table 6: Summary of the major findings. The positive sign (+) and the negative sign (-) indicate significant positive effects and negative effects, respectively.

Personal Characteristic		Direct Effect	Interaction Effect with Initiative Strategy	Interaction Effect with Task Complexity
Big-Five Personality Traits
	Conscientiousness	(+): Perceived Conversational Interaction	(+) in Mixed-Initiative: Perceived Recommendation Quality; Perceived Conversational Interaction; Perceived Trust	(+) in Simple Task: Perceived Recommendation Quality
	Extroversion	(+): Perceived Recommendation Quality
	Agreeableness		(+) in Mixed-Initiative & Complex Task: Perceived Conversational Interaction
Trust Propensity		(+): Perceived Conversation Interaction; Intention to Use		(-) in Complex Task: Perceived Effort (+) in Complex Task > Simple Task: Intention to Use
Music Sophistication		(+): Intention to Use	(+) in User-Initiative: Perceived Recommendation Quality	(+) in Simple Task: Perceived Recommendation Quality

Key Finding #1: Users with higher conscientiousness have a better perception of system competence and show more trust toward the Mixed-Initiative system. Our results demonstrate that users with a higher level of conscientiousness have more positive perceptions in terms of both recommendations and conversational interaction with the Mixed-Initiative system, engendering higher trust in the CRS [see Figures 4(a),  4(b) and 4(c) ]. This finding is in line with previous studies showing that more conscientious people have higher trust in automation when conducting decision-making tasks [15, 16]. Highly conscientious users tend to be cautious, responsible [33], and may have maximising tendencies (i.e., the tendency to explore and compare alternatives, and look for the best option) [51], which may result in more appreciation for the suggestions from the system that may help them become more informed to make a confident decision. This finding also suggests that individual differences in users’ decision-making style, i.e., maximizing (examining more alternatives to select the best option) and satisficing (settling for a good-enough option) [35, 67], may be influential on user trust in CRSs, which can be investigated in future research.

Design Implications: Trustworthy CRS design should consider users’ personality traits, especially conscientiousness. For users with higher conscientiousness who like to carefully consider all facets before making a choice, the Mixed-Initiative system that supports both user-initiative and system-initiative interactions is more desirable. System-initiated guidance may support conscientious users in seeking alternatives and finding the “perfect” items from recommendations, hence fostering user trust toward the system. However, for users with lower conscientiousness, the level of system-initiative can be relatively lower because those users tend to be casual and impulsive and might not appreciate extensive guidance from the system.

Key Finding #2: Users’ trust propensity positively influences user trust in conversational recommenders, but the degree of influence is affected by the task complexity. Our results imply the positive effects of trust propensity on users’ perceptions of the conversational interaction and their intention to use, which is consistent with previous reports of the positive effect of one's general tendency to trust others or technology on trust in recommender systems [12, 72]. Moreover, the complexity of the performed task tends to strengthen this effect [see Figures 5(b) and 5(c) ], suggesting a stronger influence of trust propensity when users perform the Complex Task. We found that users with higher trust propensity perceived much less effort and higher intention to use the system than users with lower trust propensity, but this trend was more significant for the Complex Task than the Simple Task. We argue that, when performing a complex task, users with higher trust propensity are more likely to take advantage of an effective conversational interaction to indicate what they like or dislike and obtain system guidance when they get stuck on a task. However, as shown in our model (Figure 3), users with lower trust propensity benefit less from conversational interaction, which has a strong influence on user trust (in terms of both perceived conversational interaction and intention to use).

Design Implications: CRS researchers have attempted to improve recommendation quality and conversation interaction to build user trust in the system. However, previous studies have not adapted the design of trustworthy CRSs to users’ trust propensity. The “one size fits all” approach can be flawed because it assumes all users have the same trust propensity level. Thus, future design of CRSs could also consider users’ general tendency to trust technology. For example, the system may help users with lower trust propensity understand more about the system's ability and guide them to accomplish simple tasks in the initial period, which would improve their initial trust in the system's competence.

Key Finding #3: Users with stronger domain knowledge have a higher intention to use conversational recommenders and prefer to explore recommendations by themselves. Our results indicate that users with more domain knowledge (i.e., higher musical sophistication in our case) have a higher intention to use the CRS. Furthermore, users with a higher level of domain knowledge benefit more from the conversational interaction with recommendations, because they possess a greater ability to articulate their preferences than do domain novices [32]. In addition, system-initiative suggestions are more helpful for users with less domain knowledge when looking for recommendations. In contrast, domain-knowledgeable users tended to have a better perception in finding recommendations by themselves, probably because this type of user desires more control over their decisions [38].

Design Implications: This finding informs that the users’ domain knowledge level should be taken into account in the design of CRSs, because it influences users’ intention to use the system as well as their preferred initiative strategies. For example, the Mixed-Initiative system is more beneficial for novice users as they may need more suggestions from the system to find recommendations that fit their interests. In contrast, the User-Initiative system might be sufficient for domain experts because they often expect higher control over the interaction with the system and to be interrupted less by the system-initiated guidance.

Before concluding this paper, we highlight some limitations of our research. First, the factors that influence user trust in conversational systems are not limited to Competence Perception, which was the only dimension investigated in our study. Anthropomorphism [68], security and privacy [20] are additional relevant dimensions of user trust. However, these dimensions are frequently discussed in the context of user trust in customer service chatbots and are influenced by additional personal characteristics, such as affective states [2] and privacy concerns[65]. To avoid added complexity, our trust model mainly considers the dimension of Competence Perception of CRSs, namely, perceived recommendation quality, perceived effort, and perceived conversational interaction. Second, recommender systems are applied in various domains including media, e-commerce, and healthcare. However, we conducted our study with a CRS designed only for music recommendations, which may limit the generalizability of our findings to other domains. In light of differences in user involvement levels [14], user trust is more crucial in certain domains, such as e-commerce and healthcare. Future work will validate our findings in different CRS application domains. Third, we only considered a text-based CRS for this investigation, and the results may differ when users interact with a voice-based CRS. In future work, we plan to investigate whether our results are applicable to the voice-based CRS.