Introduction

In the present day, organizations worldwide tend to structure their work around teams and workgroups¹ to perform more rapidly, flexibly, and adaptively (^{Kozlowski & Ilgen, 2006}). The various applications of teams in organizations have led to an approach that emphasizes their nature as finalized systems and the emergence of a new focus dedicated to this issue: effectiveness (^{Mathieu, Maynard, Rapp, & Gilson, 2008}). Because the effectiveness of teams matters for individual, organizational, and societal well-being, it is essential to study processes to promote it (^{Kozlowski & Ilgen, 2006}).

According to ^{Bass (1999)}, changes in the marketplace and in the workforce led to a need to adopt a transformational leadership style. These leaders foster followers in going beyond immediate self-interests, elevating their maturity as well as showing concern for achievement, self-actualization, and well-being of subordinates (^{Bass, 1999}). They also influence followers’ values, emotions, and attitudes and motivate them to perform beyond their expectations (^{Yukl, 2012}). By guiding employees towards greater levels of achievement, transformational leadership has become crucial to promoting team effectiveness.

The literature about transformational leadership theory and effectiveness supports the association between these two constructs (^{Avolio, 2010}). Various studies demonstrate that perceived transformational leadership is related to positive team outcomes in various work settings, both public and private (^{Bass & Bass, 2009}; ^{Trottier, Van Wart, & Wang, 2008}).

Although research has mainly focused on the direct effects of transformational leadership on team outcomes, some studies suggest that transformational leadership affects effectiveness indirectly, for instance, through the involvement of team members (Podsakoff, MacKenzie, Moorman, & Fetter, 1990; ^{Zaccaro, Rittman, & Marks, 2001}). However, the process by which transformational leaders exert their influence, through mediating variables, on followers’ team effectiveness has not been sufficiently addressed in the literature (^{Givens, 2008}).

In this paper we propose that affective team commitment mediates the relationship between transformational leadership and team effectiveness (see Figure 1). Transformational leaders have the capacity to motivate team members to work harder and beyond what is expected for the sake of the group (^{Polychroniou, 2009}). Thus, transformational leaders make team members more committed to the team and, consequently, more likely to work together over time, implement new ways of working, and have a better work experience. Overall, team effectiveness would be enhanced (^{Strauss, Griffin, & Rafferty, 2009}). A study on sport settings (^{Van Beek, 2011}) found that affective team commitment mediates the relation between transformational leadership and team performance. In the present study, we extend the analysis of the mediating role of team commitment in the relationship between transformational leadership and team effectiveness, using organizational teams. Moreover, we expand on previous research, taking into consideration other criteria of team effectiveness, namely team viability, team process improvement, and quality of group experience.

Figure 1 Hypothesized Model. 

Transformational Leadership and Team Effectiveness

Transformational leadership has been one of the most widely studied leadership theories over the last three decades (^{Bass, 1991}; ^{Judge & Piccolo, 2004}; ^{Zhu, Newman, Miao, & Hooke, 2013}). The theory was introduced by ^{Bass (1985)}, who developed ideas laid down by ^{Burns (1978)}. Transformational leadership was conceptualized as being composed by four independent dimensions, known as the four “I”s (^{Bass, 1985}; ^{Bass & Avolio, 1994}; ^{Judge & Piccolo, 2004}): inspirational motivation (the sense of drive that the leader inspires in followers and that produces additional, goal-oriented energy for the group or organization), intellectual stimulation (the boost in creativity in followers that the leader stimulates by encouraging an independent and innovative way of thinking), idealized influence (exemplary behaviour of the leader that generates respect and trust and makes followers proud of their group and organization), and individualized consideration (perception that the leader genuinely cares for followers and their well-being).

In a review of the literature focused on transformational leaders’ behaviours, ^{Podsakoff et al. (1990)} concluded that such leaders typically show six core behaviours: identification and articulation of a vision, implementation of an appropriate model, encouragement to accept group goals, high performance expectations, individualized support to staff, and intellectual stimulation. Based on this model, ^{Carless, Wearing, and Mann (2000)} distinguished between leaders’ behaviours that provide support to staff and those that encourage their individual development. Hence, their model describes seven behaviours implemented by transformational leaders: (1) communicating a vision, (2) developing staff, (3) providing support, (4) empowering staff, (5) being innovative, (6) leading by example, and (7) being charismatic. These behaviours may have a strong impact on team processes and also on team effectiveness, which is the focus of this study. But what is team effectiveness and how is it defined?

^{Cohen and Bailey (1997)} categorized effectiveness into three categories: performance, attitudes, and behaviours. However, criteria to define team effectiveness have changed over the past decade to include many different forms and combinations. In this sense, what constitutes “effectiveness” has become more complex in recent years (^{Mathieu et al., 2008}).

Despite the availability of many perspectives and representations of team effectiveness (^{Lourenço, Miguez, Gomes, & Carvalho, 2004}), team effectiveness is a concept that is not easy to define, since it does not correspond to an objective reality. Rather, it has been proposed that effectiveness should be analysed and measured according to the values, interests, and preferences of the actors and systems to which it refers to (^{Dimas, Alves, Lourenço, & Rebelo, 2016}).

^{Hackman (1987)} provided a model of team effectiveness that received strong support. According to this model, team effectiveness is defined and can be evaluated using three different criteria: 1) the degree to which team’s product or service meets, or exceeds, the standards of quantity and quality of those who receive, review, and/or use it; 2) the degree to which social processes within the team maintain, or enhance, the ability of the group to work together and become a more competent and better-performing unit over time; 3) the degree to which the group experience satisfies members’ needs and increases members’ satisfaction, well-being, and development (^{Hackman, 1987}; 2012).

In line with this embracing perspective, in the present paper we consider three criteria to evaluate team effectiveness: team viability, which can be defined as the capacity of the team to adapt to changes and to cope with challenges in an ever-changing environment (^{Aubé & Rousseau, 2005}; ^{Boies & Howell, 2009}); team process improvement, the capacity of team members to enhance existing processes and find innovative ways to improve team outcomes (^{Kirkman, Rosen, Tesluk, & Gibson, 2004}); and quality of group experience, which is the degree of positive social climate within the working group (^{McGrath, 1991}).

A positive relation has been observed between transformational leadership and team viability (^{Boies & Howell, 2009}). Other studies revealed a positive and direct relationship between transformational leadership and innovative work behaviours, which is related to team process improvement, since both concern the ability of the team to implement new ways of working (^{Gumusluoglu & Ilsev, 2009}; ^{Reuvers, Van Engen, Vinkenburg, & Wilson-Evered, 2008}). Also, ^{Van Dierendonck, Haynes, Borrill, and Stride (2004)} found that transformational leadership has a positive relation with the well-being of followers, which is close to the concept of quality of group experience. For these reasons, we expect transformational leadership to be positively related to the three criteria of team effectiveness we are considering in this study.

Therefore, based on these considerations, the results of previous studies, and in line with ^{Hackman’s (1987)} model, we introduce the first hypothesis of this study:

H1: Transformational leadership will be positively related to team viability (H1a), to team process improvement (H1b), and to quality of group experience (H1c).

Transformational Leadership and Affective Team Commitment

Transformational leadership has been related to followers’ identification with the leader and consequently social identification with the group or organization concerned (^{Kark, Shamir, & Chen, 2003}). For this reason, the leadership style has been considered a main determinant of organizational commitment (^{Avolio, Zhu, Koh, & Bhatia, 2004}; ^{Mowday, Porter, & Steers, 2013}).

According to ^{Meyer and Allen (1991)} and ^{Allen and Meyer (1996)}, organizational commitment is represented by three distinct dimensions: affective commitment (the affective orientation toward a group or organization), normative commitment (the perception of obligations to remain in the organization), and continuance commitment (the recognized costs of leaving the organization).

Several authors (e.g., ^{Kozlowski & Ilgen, 2006}) consider commitment as a valuable team state to predict team effectiveness. Affective commitment denotes an emotional relationship that the individual develops toward the organization, associated with the identification and involvement with it (^{Martins, Rebelo, & Tomás, 2011}). ^{Meyer and Allen (1991)}, affirmed that affective commitment is likely to have the greatest impact on an employee’s organization-relevant behaviour; later, ^{Meyer, Becker, and Vanderberghe (2004)} reported that “research shows that affective commitment has the strongest positive correlation with job performance, organizational citizenship behaviour, and attendance, followed by normative commitment” (p. 993), while continuance commitment seems to be unrelated, or negatively related, to these behaviours. Thus, considering the stronger relation of affective commitment with employees’ job-relevant behaviours, in this study we focus on affective commitment and, in particular, on affective team commitment. It has in fact been observed that commitment to a specific target, for instance one’s own team, would be a better predictor of behaviours relevant to that target than a general organizational commitment (^{Herscovitch & Meyer, 2002}). ^{Hsu and Mujtaba (2011)}, for example, focused their attention on team level commitment.

^{Bass (1999)} suggested that there is a clear need for better understanding how transformational leadership influences employees’ work-related attitudes, such as affective team commitment. Previous studies showed that transformational leadership is positively associated to organizational commitment because such leaders promote acceptance of the value associated with the organizational goals, mission, and vision (^{Avolio et al., 2004}). According to the social exchange theory, we can infer that when leaders treat team members with respect and consideration, they tend to reciprocate with positive behaviours towards the leader and the team itself (^{Blau, 1964}). Based on this theory, it is expected that transformational leadership will enhance affective commitment towards the team (^{Strauss et al., 2009}). Thus, we hypothesize that:

H2: Transformational leadership will be positively related to affective team commitment.

Affective Team Commitment and Team Effectiveness

Affective team commitment can produce different positive outcomes. Involving the experience of positive affective states, it can encourage team members to engage in proactive behaviours (^{Parker, 2007}), promote unstructured and original behaviours (^{George, 1990}), and encourage individuals to set harder and more stimulating objectives (^{Isen & Reeve, 2005}). Several studies have found that affective team commitment is positively related to some dimensions of team effectiveness, such as perceived team member proficiency (^{Strauss et al., 2009}) and willingness to promote initiatives to improve (^{Ng, Feldman, & Lam, 2010}). These studies suggest that employees affectively commit to team work plans, specify team tasks in advance, and are willing to improve the team in terms of products and processes. Affective team commitment was also found to be strongly correlated with positive affect, which is at the base of team viability and quality of group experience (^{Marchand & Vandenberghe, 2013}). ^{Bentein, Vandenberghe, Vandenberg, and Stinglhamber (2005)} in their longitudinal study also observed that affective team commitment was negatively related to turnover intentions. Turnover intentions refer to the intention to leave the team, which can undermine team viability. It is supposed that when team members have emotional attachments to their teams and are really committed to them, they behave in ways that produce beneficial outcomes to the teams (^{Van Beek, 2011}), thus improving team processes and team outputs.

Therefore, based on the previous literature and extending the empirical studies that have been conducted, we propose the following hypothesis:

H3: Affective team commitment will be positively related to team effectiveness, namely to team viability (H3a), team process improvement (H3b), and quality of group experience (H3c).

Transformational Leadership, Affective Team Commitment and Team Effectiveness

Although functions of transformational leadership have been extensively examined, reviewing literature on leadership behaviours that help the team to make good and appropriate use of its collective resources when performing a task, ^{Hackman and Wageman (2005)} indicated that leadership studies should focus much more on conditions that foster team effectiveness. However, an increasing number of studies (e.g., ^{Moynihan, Pandey, & Wright, 2012}) suggests that a large part of the influence that transformational leadership generate is tangible but indirect. Thus, in other words, leaders promote conditions for team success directly, but even more by shaping key mediating variables.

During the past decade, researchers have begun to give more attention to “mediating processes that explain why certain inputs affect team effectiveness and viability” (^{Ilgen, Hollenbeck, Johnson, & Jundt, 2005}, p. 519). For example, despite the direct effect of transformational leadership on innovation processes (^{Gumusluoglu & Ilsev 2009}; ^{Reuvers et al., 2008}), a recent study conducted with teams of nurses found that transformational leadership did not influence innovation behaviours directly, but through patient safety climate and innovation climate (^{Weng, Huang, Chen, & Chang, 2015}). Similarly, in a study conducted in military settings, the relation between transformational leadership and team viability was mediated, partially and significantly, by the positive affective processes of team members (^{Boies & Howell, 2009}).

Although transformational leadership has a very important direct effect on outcomes, we believe that it may also indirectly affect team effectiveness when team members are committed to the team. Bass and ^{Bass (2009)} suggest that transformational leadership increases team effectiveness because of its impact on proactive work role behaviours, and according to ^{Strauss et al. (2009)} and ^{Parker (2007)}, proactive work role behaviours are strongly related to affective commitment.

Transformational leaders have the capacity to motivate followers to do more than normally expected, raising their awareness of (new) outcomes and motivating them to transcend their own interests for the sake of the team (^{Polychroniou, 2009}). Thus, transformational leaders that are able to make employees more committed to their team can indirectly enhance several team outcomes. Supporting this assumption, ^{Van Beek (2011)} found a positive correlation between transformational leadership, team commitment, and team performance in sport team environment. In addition to team performance, we believe that affective team commitment might be a mediator between transformational leadership and other dimensions of team effectiveness. Making team members emotionally committed to their team, transformational leaders would engage their followers in implementing innovative ways of working (team process improvement), having a better experience of the team work (quality of group experience) and working together over time (team viability). Thus, in this study, we examine if transformational leadership has both a direct relationship and an indirect relationship, through affective team commitment, on the three team effectiveness outcomes, namely: team viability, team process innovation and quality of work team experience. Hence, we hypothesize that:

H4: Affective team commitment will mediate the relationship between transformational leadership and team effectiveness, namely, between transformational leadership and team viability (H4a), team process improvement (H4b), and quality of group experience (H4c).

Method

Results

Preliminary Analysis

Before testing the hypotheses, we analysed the psychometric properties of the Team Affective Commitment scale, since the team adaptation of this scale was not previously validated for the Portuguese language. The total sample was randomly divided into two sub-samples in order to obtain evidence of cross-validity. In the first sub-sample, composed of 220 subjects, we conducted an exploratory factor analysis (EFA), while in the second sub-sample, composed of 225 subjects we conducted a confirmatory factor analysis (CFA).

Before performing the EFA we checked if scores were normally distributed and the factorability of the correlation matrix. The Kaiser-Meyer-Olkin measure of sampling adequacy and Bartlett’s test of sphericity showed good results, KMO = .80, χ²(15) = 541, p < .001. Thus, we ran the EFA with principal components extraction. The factorial solution showed one factor, with all item loadings higher than .55. The Cronbach’s alpha of the scale was .82.

Then the model obtained through the EFA was tested using CFA. Following the recommendations of ^{Byrne (2010)}, we checked the chisquare test, the CFI (comparative fit index), and the RMSEA (root mean square error of approximation) and its confidence interval (see Table 1). The results of the CFA indicated a poor goodness of fit, showing an inadequate adjustment between data and the hypothesized model, χ²(9) = 110.45, p <.001, CFI = .84, RMSEA = .22, intervals of confidence 90% between .19 and .26, statistically significant (Table 1). After adjustments were made considering both the statistical (namely the modification indices provided by AMOS) and the theoretical basis (removing item 3 for overlapping content and correlating errors of item 1 and item 4), a significant improvement in fit indices was obtained, χ²(4) = 3.34, p = .501, Δχ²(1) = 35.14, p < .001, CFI = 1.00, RMSEA = .00; intervals of confidence 90% between .00 and .09, statistically significant, which showed a good fit between the variance-covariance matrix and the tested model. Cronbach’s alpha was .83.

Table 1 Goodness-of-fit Indices of the Measurement Models Tested (N = 225) 

Note. N = 90 teams.*p < .05., **p < .01, ***p < .001.

Data Aggregation and Correlation Analysis

All constructs considered in this study were at team level. However, transformational leadership, team commitment, and quality of group experience measures were collected individually from each team member. To examine whether the data justified the aggregation of team-level constructs, the average deviation index (AD_M index), developed by ^{Burke, Finkelstein, and Dusig (1999)}, was computed. The average AD_M values obtained for transformational leadership (M = 0.50, SD = .028), affective team commitment (M = 0.52, SD = 0.31) and quality of group experience (M = 0.40, SD = 0.27) were below the upper-limit cut-off criterion of 0.83 suggested by the authors. This revealed that the level of agreement within the teams was sufficient to aggregate team members’ scores with confidence to the team level. Furthermore, we checked if such aggregation was justified calculating the intraclass correlation coefficients ICC(1) and ICC(2) (^{Bliese, 2000}) with the tool developed by ^{Biemann, Cole, and Voelpel (2012)}. The ICC(1) value for transformational leadership (GTL) was .33, the ICC(1) value for affective team commitment was .16, and the ICC(1) value for quality of group experience was .22, whereas the ICC(2) values for the same variables were .71, .49, .58, respectively. Overall, the values were in line with the values considered acceptable in the literature (^{Bliese, 2000}; ^{Klein & Kozlowski, 2000}) and provided support for aggregating data to team level.

Table 2 reports means, standard deviations, AD_M, ICCs, correlations, and reliability coefficients of the variables considered in this study. Team size was included as control variable and only quality of group experience was significantly related to team size. Table 2 shows that correlations between all variables considered are positive and significant, which is in line with what was expected in the hypotheses.

Table 2 Descriptive Statistics, Scale Reliabilities, ADM, ICCs, and Correlations between Variables 

Note. TL = transformational leadership; ATC = affective team commitment; QGE = quality of group experience. Reliability coefficients (Cronbach’s alpha) are reported in brackets. N = 90 teams.*p < .05, **p < .01, ***p < .001.

Hypotheses Testing

We tested our hypotheses using structural equation modelling. A path analysis model was studied using AMOS software. This approach allows the indirect effects in the model to be estimated (^{Preacher & Hayes, 2008}). We used scale means as single indicator for each construct in the study. The aggregated database was used for this analysis (N = 90 teams). Parameters of the model were estimated through the maximum likelihood method. In the model, on the basis of the observed significant correlation, we also controlled the effect of team size on the quality of group experience. Table 3 shows that the findings of the first model (M1) indicated a poor goodness of fit between data and the hypothesized model, χ²(6) = 28.35, p < .001, CFI = .86; RMSEA = .20, intervals of confidence 90% between .13 and .28, statistically significant. Because conditions suggested by ^{Kline (2011)} were not met by the model (χ²/df ratio < 3, CFI > .90, and RMSEA < .08), this revealed the need to adjust it. The modification indices (MI) provided by the AMOS program indicated the existence of a high modification rate for the covariance of the error of indicator team viability and the error of team process improvement (MI = 21.4). Thus, we added a covariance parameter between the residual parameters of team viability and team process improvement. We did so based on the suggestions of ^{Schreiber, Nora, Stage, Barlow, and King (2006)}. According to these authors, parameter constraints may be changed to improve the fit of the model if such modifications are justified theoretically. So, besides the statistical reasons provided by the software, we expected that the two criteria would be correlated to each other because they represent dimensions of the same construct, which is team effectiveness (^{Mathieu et al., 2008}). Finally, Table 2 confirms that these two criteria are highly correlated (r = .56). This procedure allowed a significant improvement in the quality of fit indices, M2: χ²(5) = 3.93, p > .05, Δχ² = 24.42, p < .001, CFI = 1.00, RMSEA = .00, intervals of confidence 90% between .00 and .13, not significant, revealing a good fit between data and the hypothesized model (see Table 3).

Table 3 Comparison of First and Second Model 

N = 90 teams.*p < .05, **p < .01, ***p < .001.

Once it was established that Model 2 was superior to Model 1, we went through the analysis using bootstrap approximation using a two-side bias-corrected 95% confidence interval with 1,000 samples. Standardized direct and indirect (mediated) effects were estimated (Figure 2) to provide further empirical evidence for our hypotheses (^{Hayes & Scharkow, 2013}).

Hypothesis 1 concerned the direct positive relationship between transformational leadership and the three criteria of team effectiveness. The estimated direct effects of transformational leadership on team viability (β = .27, p = .02) and quality of group experience (β = .26, p = .002) were significant, but not the direct effect on team process improvement (β = .21, p = .07). These results provided support for Hypotheses 1a and 1c but not Hypothesis 1b.

Hypothesis 2 concerned the direct positive relationship between transformational leadership and affective team commitment. The estimated direct effect of transformational leadership on affective team commitment (β = .54, p = .001) was significant. This result provided support for Hypothesis 2.

Hypothesis 3 concerned the direct positive relationship between affective team commitment and the three criteria of team effectiveness. The estimated direct effect of affective team commitment on quality of group experience (β = .56, p = .001) was significant, on team process improvement was not significant (β = .22, p = .06), and on team viability (β = .14, p = .24) was not significant. These mixed results provided support for Hypothesis 3c, but failed to support hypotheses 3a and 3b.

Standardized estimates

*p < .05, **p < .01.

Figure 2 Results of Path Analysis Model. 

Hypothesis 4 stated that affective team commitment mediates the relationship between transformational leadership and the three criteria of team effectiveness. The results showed that the estimated indirect effects (Table 4) of transformational leadership through affective team commitment on team viability was .07 (p = .18), on team process improvement was .12 (p = .04), and on quality of group experience was .30 (p = .001). Because the direct path between transformational leadership and quality of group experience (β = .26, p = .004) remained significant, we can support the hypothesis that affective team commitment positively and partially mediates the relationships between transformational leadership and quality of group experience. Conversely, Hypotheses 4a and 4b were not supported.

Table 4 Indirect Effects through Affective Team Commitment 

Note. N = 90 teams.*p < .05, **p < .01.

Discussion

Transformational leadership plays a crucial role in teams and contributes to their overall effectiveness (e.g., ^{Boies & Howell, 2009}; ^{Reuvers et al., 2008}). At the same time, an essential role is represented by affective team commitment that is fundamental to several aspects of team effectiveness (e.g., ^{Neininger, Lehmann-Willenbrock, Kauffeld, & Henschel, 2010}; ^{Strauss et al., 2009}).

Contributing to the literature on transformational leadership and in line with the previous findings, our results supported the hypothesis that leaders who adopt a transformational style of leadership are able to generate positive results in team viability and quality of group experience (Hypotheses 1a, 1c). This means that transformational leaders may boost the effectiveness of their teams by encouraging team members to cope with environmental challenges and motivating them to continue to stay and work together. We expected this direct effect also on team process improvement (Hypothesis 1b). However, the effect of transformational leadership on this dimension appears not to be statistically significant. This dimension implies removal of defects or deficiencies, and establishment of new practices to increase productivity. It is possible that the influence of the leader is not sufficient to push team members to improve in this direction.

In line with previous literature, our findings support the hypothesis that leaders with a transformational style have a positive effect on the affective commitment that members have toward their teams (Hypothesis 2). Thus, team members that are led by a transformational leader will be emotionally committed to their respective team. According to the social exchange theory (^{Blau, 1964}), the positive relationship with the leader is reciprocated with a stronger affective commitment to the team and the desire to significantly contribute to its development by working harder within the team itself.

Experiencing affective team commitment seems to have positive effects also on other aspects of overall team effectiveness. In line with the existing literature, our findings support the hypothesis that team members emotionally bonded to their team have also a group experience of better quality (Hypothesis 3c). This result is in line with and extends previous studies that showed the relation between affective commitment and positive affective processes (^{Boies & Howell, 2009}; ^{Marchand & Vandenberghe, 2013}); affective team commitment in fact has an impact not only on individual positive emotions but also supports and promotes the experience of positive social relationships among team members.

The literature review suggests that teams in which members are emotionally committed would also report better outcomes in terms of team viability (Hypothesis 3a) and team process improvement (Hypothesis 3b). However, these two hypotheses were not supported: even if correlations between affective team commitment and team viability, and team process improvement, respectively, showed positive significant relations, when, in our path analysis model, affective team commitment is examined with these two criteria of team effectiveness together, its effect loses statistical significance. Regarding team viability, the emotional bond with the team does not seem sufficient to justify the capability of team members to keep working together to cope with challenges. Similarly, for team process improvement, affective team commitment does not seem capable of promoting the implementation of innovative ways of working. In order to innovate team processes and products, teams might need, in addition to team affective commitment, technical skills and/or organizational and cognitive resources, such as skills in the task domain, motivation to innovate, or individual and team learning behaviours (^{Amabile & Pratt, 2016}). However, it has to be highlighted that the relation between team affective commitment and team process improvement was almost marginally significant (p = .06). Thus, the relation between these two variables is worth further examining in future studies.

The main objective in this research was to study the effect of the affective dimension of commitment on overall team effectiveness, when shaped by the transformational leadership style of the team direct supervisor. According to our findings, it seems that transformational leadership has both a direct effect and also an indirect effect, through affective team commitment, on quality of group experience. Thus, affective team commitment positively and partially mediates the relationship between transformational leadership and quality of group experience. This means that the experience of positive social climate within the team is improved when team members are emotionally committed to the team and such commitment is generated by the transformational style of their leaders. This result corroborates the idea that affective aspects such as quality of group experience are strongly affected by affective/motivational team processes and states as it is the case of affective team commitment (^{Kozlowski, Grand, Baard, & Pearce, 2015}). This effect is especially relevant when the latter is shaped by transformational leadership.

In contrast with our expectations, the findings do not support the hypothesis concerning the mediating effect of affective team commitment between transformational leadership and team viability. This could mean that transformational leaders may indeed have an effect on the capability of their team to work over time (significant direct effect), but that this might not be affected by the capability of the leader to make team members emotionally committed to the team. Several considerations need to be made about this. First, further research is needed to check if this effect is consistent in other studies. Then, different typologies of teams should be tested as well. ^{Boies and Howell (2009)} showed that positive affect positively mediates the relation between transformational leadership and team viability. However, it has to be pointed out that such findings were observed in military settings. Our sample is composed of teams formally constituted within work organizations that have been working together for five years on average, and thus it might be that their capability to keep working together as a whole is shaped by other variables beyond the affective commitment with the team. For instance, it might be interesting to study the role of other mediators such as team climate (^{Pirola-Merlo, Härtel, Mann, & Hirst, 2002}) or network structure (^{Balkundi & Harrison, 2006}).

The hypothesis that affective team commitment would mediate the relation between transformational leadership and team process improvement was not significant either. However, it is important to highlight that the level of significance obtained (.06) was near statistical significance. This could mean that transformational leaders may push their team members to create and implement some improvement in their ways of working by shaping their affective commitment, but also by influencing other variables, such as innovation climate (^{Weng et al., 2015}). This means that, although team affective commitment is a variable to take into consideration in the relationship between transformational leadership and team process improvement, other variables need to be included.