**1. Introduction**

The theory of planned behavior (TPB) is popular for studying behavioral intentions. It is hypothesized that attitudes toward the behavior, subjective norms, and perceived behavioral control are the antecedents of behavioral intentions [1]. Attitudes toward the behavior refer to the extent of an individual's positive or negative reaction to a specific behavior; subjective norms refer to the extent to which an individual responds positively to the social preferences of the referent others; perceived behavioral control refers to an individual's perception of his or her confidence in performing a specific behavior [2]. For Ajzen [3], perceived behavioral control is the general state of both perceived selfefficacy (i.e., one's confidence in the ability to perform a specific behavior) and perceived controllability (i.e., one's confidence in having the resources to perform a specific behavior), which are the internal and external influences of behavioral intention, respectively. Ajzen and his colleagues are continually pushing for the latest advances and applications of the theory through their own research work [4–8]. Since it was proposed, the theory has been widely applied in various contexts (e.g., [9–11]). Moreover, the context of the current study is about students' intentions to learn sustainability knowledge (will be discussed in detail in the next section). In regard to school and college education, this theory is considered having important implications for explaining students' behavioral intentions, including college students' intentions to use a wiki for group work [2], students' intentions to take

**Citation:** Huang, H.; Cheng, E.W.L. The Role of Commitment in an Extended Theory of Planned Behavior: Test of Its Mediating Effect with Partial Least Squares Structural Equation Modeling. *Mathematics* **2022**, *10*, 1049. https://doi.org/ 10.3390/math10071049

Academic Editors: María del Carmen Valls Martínez, José-María Montero, Pedro Antonio Martín Cervantes and Seifedine Kadry

Received: 18 February 2022 Accepted: 23 March 2022 Published: 24 March 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

English courses in Chinese schools [12], Chinese students' communicative intentions [13], and college students' mobile learning intentions [14].

Although the direct relationship between the three antecedents and intentions have been extensively studied, the authors of this study would like to draw attention to the variable "commitment", which may play a role in explaining behavioral intentions. Commitment, generally referring to "a promise or firm decision to do something" (in the Cambridge Dictionary), is rarely employed in an extended TPB model. However, an individual's commitment to an organization (i.e., organizational commitment) has long been the determinant of the intention to stay or quit an organization (e.g., [15,16]). This has also been extended to the study of commitment beyond organizational commitment, such as employee and job commitment [17,18]. For example, Cuskelly and Hoye [19], studying the retention of early career sports officials, found that the commitment to officiating affected the intention to continue officiating. In a study of personal information management motivation, Hwang, Lin, and Shin [20] found a significant relationship between knowledge system commitment and knowledge sharing intentions. Moreover, Lee and Jeong [16] used a sample of 459 employees from multiple companies in South Korea and found that organizational commitment mediated the positive relationship between job insecurity and turnover intention. Based on other studies' findings that affective commitment was amongst the strongest dimension in explaining the intention to remain in a company, Orgambídez, Borrego, and Vazquez-Aguado [21] further found a significant relationship between general self-efficacy of work and affective commitment to the organization. Therefore, it would be interesting to explore whether commitments should be included in the TPB. Recently, Ajzen and Kruglanski [22] proposed the inclusion of motivation to act as a mediator between the three antecedents and intentions in explaining an intentional behavior. In a similar vein, this study posits that the TPB is extended with commitment, which attenuates the links between the three antecedents and intentions.

To test the proposed extended TPB model, this study uses partial least squares structural equation modeling (PLS-SEM). Unlike the covariance-based SEM (CB-SEM), the PLS-SEM is the variance-based SEM (VB-SEM), suitable for testing path models with nonnormal data and smaller samples [23]. Since a purposive and convenient sample was employed (i.e., violation of multivariate normality of the data) in this study, the PLS-SEM method is more appropriate to examine the hypothesized model. This study uses Warp-PLS7.0 developed by Professor Ned Kock. The Factor-Based PLS Type CFM3 algorithm is adopted because it can improve computation efficiency [24]. The robust factor-based method (also known as consistent PLS [23]), similar to the CB-SEM, is employed to account for measurement errors. In addition, this software tool can determine the structural model fit [24], which is crucial in this study to examine the mediating role of commitment. There is no shortage of studies on mediating effects in the mainstream literature (e.g., [25–27]). The test of mediating effects will be described in a later section.

#### **2. The Context of This Study**

The concept of sustainability has been integrated into primary and secondary education in China [28]. Another related term is sustainable development (SD). For Maude [29] (p. 47), sustainability refers to "a sustainable state or condition", while SD refers to "a process of economic and social change". For Liu [30] (p. 246), sustainability education (SE), also known as education for SD (ESD) or education for sustainability (EfS), emphasizes "social, economic, and environmental sustainability and the interaction of these three elements". Take geography as an example. According to China's newly revised Geography Curriculum Standard for Compulsory Education [31], students should understand the concept of SD in geography so that they can learn to become active and responsible citizens, so as to protect the environment and maintain good social characteristics of the country as well as the world. Sustainability has thus become part of the standard geography curriculum, which should contribute to the development of a holistic experience not only around philosophical and theoretical issues but also around practical ones [32].

The purpose of incorporating sustainability into education is to sustain the planet by allowing students to develop their ability to relate the concept to everyday life [33]. Because of this, SE has been added to different school curricula around the world [34]. According to Noble and McGrath [35], it is crucial for our young people to learn to be resilient before they reach adulthood. The education system should be able to foster positive attitudes in students, enabling them to think logically and to be able to distinguish right from wrong [36]. It is important to increase their understanding of sustainability during their mental development stage. In fact, SE involves not only "high-quality subject matter knowledge" but also "modern researched pedagogical content knowledge", and relies on "teachers' interpretations and transformations of subject matter knowledge" to stimulate students' interest in learning [32] (p. 2).

However, if students lack interest in or feel that they are not capable of learning sustainability, they may be reluctant to do so. Therefore, their perceptions of sustainability influence their intentions to learn sustainability because, as noted by Khudhair [37], such perceptions make a substantial contribution in driving their intentional behavior through their preferences for learning sustainability. Once they plan to study sustainability, their academic performance will improve. Existing literature contains a lot of research on students' learning intentions. For example, Cheng [25] found that students' attitudes toward e-collaboration were important in enhancing their intentions to collaborate online with group members on group projects. Likewise, the intent of learning sustainability is also worth exploring. By understanding the factors that influence students' behavioral intentions, schools can find ways to motivate students to learn sustainability. In addition, the commitment to learning sustainability may play a role in explaining students' learning intentions. Yet, the concept of learning commitment is rarely discussed in the extant literature [38]. Although infrequently used, similar terms have caught the attention of researchers. For example, students' involvement or engagement in online learning refers to their commitment to online learning [39,40]. Therefore, this study aims to fill the research gap by examining the role of commitment in an extended TPB. As such, the following research objectives have been set:

