Introduction
With the rapid growth and aging of the world population, the long-term shortage and high turnover rate of nurses have become global problems, especially so after March 2020 when the World Health Organization declared a global pandemic (Pappa et al., 2021). The epidemic of COVID-19 has adverse effects on the physical and mental health of nurses, causing exhaustion, family separation, sleep deprivation, anxiety, and depression as well as increased workloads because of higher requirements for medical care and epidemic prevention policies. All of these factors have serious effects on nursing team stability (Marvaldi et al., 2021). According to the World Health Organization, the increase in demand for care has further exacerbated the nursing shortage, which is predicted to exceed 7.6 million by 2030 (Boniol et al., 2022). Although colleges and universities have added to the number of nursing professionals during the past few years, the shortage of nurses is still a grave problem for hospital managers given the aging population in China (Wang et al., 2021). Nursing staff shortages increase the workload of working nurses, leading to job burnout and affecting the quality of nursing services (Guo et al., 2019). Work engagement is considered an effective way to reduce turnover during staffing shortfalls (Pennbrant & Daderman, 2021; Remegio et al., 2021).
The job demands-resources (JD-R) model is an important theoretical model used in the study of work engagement. In this model, job resources are recognized as a protective factor that reduces perceived job burnout in employees (Bakker & Demerouti, 2017). Research on strategies to improve work engagement in nurses based on the JD-R has developed rapidly in recent years (Addimando, 2019). However, most of the studies on job resources in the JD-R focus more on the external resources (organizational variables) available in the work environment and ignore the role of internal resources such as personal characteristics. Internal resources may be valued in the JD-R model because work engagement, as the embodiment of individual psychological states, is greatly influenced by personal characteristics. Therefore, this study was designed to explore the factors influencing work engagement in nurses at both the individual level (achievement motivation and self-efficacy) and organizational level (professional nursing practice environment [PNPE]).
Research Framework
Demerouti et al.'s (2001) theory of the JD-R model provided the theoretical basis of this study. Schaufeli et al. (2002) proposed a model that emphasizes two kinds of work characteristics: job demands and job resources. Job demands refer to the material, psychological, social, or organizational aspects of a job that require continuous efforts or skills that demand physical and mental effort. These demands differ in each workplace and are not negative per se. However, if they exceed an employee's coping ability, they may become a source of stress. Unlike job demands, job resources have a motivating effect and can prevent job burnout and lead to higher work engagement (Bakker & Demerouti, 2017). Job resources may be defined as helping employees achieve work goals; reducing work demands; relieving physical and psychological consumption; and stimulating personal growth, learning, and development (Demerouti et al., 2001; Kato et al., 2021).
Demerouti et al. (2001) noted that job resources are the best indicator of engagement in both individual and organizational performance via a motivational process. Their model also emphasized the role of employees' personal resources (e.g., psychological capital, self-efficacy, and achievement motivation), which are defined as employees' positive self-evaluation or control belief in the environment. Job resources are positively correlated with employee engagement and performance and reduce the negative impact of job demand (Bakker & Demerouti, 2017).
Work Engagement
Work engagement refers to a substantial and continuous work-related mental state characterized by vigor, dedication, and absorption. Vigor refers to a high level of energy invested by individuals in their work. Dedication refers to an individual's passionate and responsible attitude toward their work. Finally, absorption refers to an individual's complete concentration on work, accompanied by a comfortable and harmonious state and self-perception of the rapid passage of time (Schaufeli et al., 2002). Engagement as a construct has been widely studied because it involves various positive outcomes in employees and organizations. This construct has been positively correlated with employees' mental well-being, job competency, and career satisfaction (Addimando, 2019). In addition, it has been associated with organizational behaviors such as turnover rate, organizational commitment, and service quality (Shanafelt & Noseworthy, 2017).
Professional Nursing Practice Environment, Self-Efficacy, and Work Engagement
Against the background of the increasing global nursing demand and shortage of nurses, many scholars have noted that the characteristics of some hospitals make them "magnetic." Organizational empowerment, sufficient staff and equipment resources, and harmonious nurse-physician relationships may be considered good characteristics of a PNPE (Shanafelt & Noseworthy, 2017). Previous research has shown that the attribute of being a PNPE positively predicts work engagement (Addimando, 2019). For example, nurses practicing in American Nurses Credentialing Center Magnet hospitals as well as other positive service environments reported relatively high levels of work engagement (Cosme et al., 2021). Similarly, a higher quality working environment, lower social dysfunction, and lower work burden are closely related to the two elements of work engagement: vitality and dedication (Jedwab et al., 2021).
Self-efficacy refers to a person's ability to engage in a certain behavior in a specific situation and to achieve the expected results (Bandura, 1982). Nurses with high levels of nursing professional self-efficacy can effectively use their skills to accomplish things beyond their ability when faced with major obstacles (Kim et al., 2022). Self-efficacy is dynamic and may be changed by learning, feedback, and experience (Croy et al., 2020). Previous research in the literature has shown PNPE to be a significant predictor of self-efficacy (Wallin et al., 2021). Positive emotional attitude in employees is stimulated by perceived organizational empowerment. A survey was conducted on 300 pediatric registered nurses in Jilin Province, with results showing self-confidence and enthusiasm for work to be closely related to the degree to which they self-perceived their work environment as supportive (Cheng et al., 2020). In addition, Kittel et al. (2021) claimed that healthy workplace characteristics such as harmonious nurse-physician relationships may influence hospital affairs and were shown to be a protective factor for midwives in terms of improving their self-efficacy and quality of life. The following two hypotheses are supported in the above and were investigated in this study:
Hypothesis 1. PNPE is an antecedent of work engagement.
Hypothesis 2. PNPE is an antecedent of self-efficacy.
Furthermore, the results of previous research indicate that nurses with higher self-efficacy exhibit increased motivation with regard to work engagement (Wallin et al., 2021). Self-perceiving a supportive working environment is a significant factor influencing nurses' sense of self-worth and willingness to devote themselves to their work (Trepanier et al., 2020). PNPE (evidenced by nurses participating in hospital affairs, nursing foundations for quality of care, effective and visible nursing leadership, friendly medical relations, and resource adequacy, among other indicators) can significantly and positively impact on nurses' self-efficacy, work engagement, turnover intention, and career development. The following hypothesis is supported in the above and was further investigated in this study:
Hypothesis 3. Self-efficacy mediates the relationship between PNPE and work engagement.
Mediating Role of Achievement Motivation
Achievement motivation refers to the driving force of the individual pursuit of success as well as efforts and persistence in the face of challenges (Richter et al., 2021). Achievement motivation may be divided into two dimensions: motivation for success and motivation to avoid failure (Cadenas-Sanchez et al., 2021). Specifically, when an individual's behavior is dominated by the pursuit of success, it manifests as striving for progress and active efforts. In contrast, when an individual's behavior is dominated by a desire to avoid failure, it manifests as anxiety, retreat, and hesitation (Mahdavi et al., 2021).
The findings of previous research have shown that employees exhibit better engagement when influenced by the achievement motivation (Tuominen et al., 2020). Achievement motivation belief is considered to be an important predictor of personal career development and organizational performance (Emamjomeh et al., 2021). Individuals with a strong motivation for success are more likely to have the confidence necessary to overcome setbacks and are more willing to devote themselves to their work and make unremitting efforts to achieve their goals. Bakker and van Wingerden (2021) claimed that individual self-efficacy and the motivation to pursue success can encourage workers to consciously regulate their work behavior and show positive abilities for self-control. Hsu et al. (2010) conducted a cross-sectional survey of 121 male nurses in Taiwan and showed that achievement motivation was positively predicted by occupational environment (e.g., workload, quality of working life). Furthermore, achievement motivation was found to mediate the relationship, explaining the strong motivation of nurses to pursue success and avoid job burnout in supportive practice environments (Hsu et al., 2010). The following hypothesis is supported in the above and was further investigated in this study:
Hypothesis 4. Achievement motivation mediates the relationship between PNPE and work engagement.
Methods
Participants
A cross-sectional survey employing a convenience sampling design was used in this study. Participants from four tertiary hospitals (two general hospitals, one maternity and children's hospital, and one oncology hospital) in Chengdu were enrolled from January to June 2020. The research assistants randomly selected six departments from each hospital to distribute questionnaires. Inclusion criteria for participants were nurses who (a) had worked in the same nursing position for more than 3 months and (b) agreed to participate voluntarily. The exclusion criteria were (a) interns and nurses engaged in advanced studies and (b) nurses who were currently sick, pregnant, or undergoing training. Five hundred sixty participants completed the survey. Questionnaires were excluded under the following conditions: when questionnaires from the same hospital exhibited exceptionally comparable (i.e., mutually copied) responses, when the answers to the questionnaire followed a pattern (i.e., select option "A" for all questions), when multiple answers were given to a single-choice question, or when over 5% of the items on the questionnaire were left unanswered. For questionnaires missing less than 5% of the items, the mean imputation method was used. After filtering, 515 of the questionnaires were considered valid and used in the analysis.
On the basis of the estimation method of sample size recommended by Bentler and Chou (1987), 5-10 participants are required per estimated parameter. In light of the 96 parameters in this study, the required sample size was 480-960. Thus, the 515 participants in this study were sufficient to analyze the hypothesized model.
Data Collection
Data collection instruments included the demographic information sheet and four scales for measuring PNPE, self-efficacy, achievement motivation, and work engagement.
Demographic Information Sheet
The demographic information sheet was designed by the researchers and included age, gender, marital status, department, educational level, professional title, job tenure, current position, and work purpose.
Practice Environment Scale of the Nursing Work Index
PNPE was measured using the Chinese version of the Practice Environment Scale of the Nursing Work Index (PES-NWI; L. F. Zhang et al., 2014), originally developed by Lake (2002). The PES-NWI contains 31 items and is divided into five dimensions: nurse participation in hospital affairs (nine items); nursing foundations for quality of care (10 items); staffing and resource adequacy (four items); nurse manager ability, leadership, and support of nurses (five items); and collegial nurse-physician relations (three items). Responses are rated on a 4-point Likert scale from 1 (strongly disagree) to 4 (strongly agree). The summed score of all items is the total PNPE score, with higher scores indicating higher levels of PNPE. In this study, the overall Cronbach's [alpha] for the scale was .86, and the [alpha] for each dimension ranged from .82 to .89. Test-retest reliability was .84, and split-half reliability was .82.
General Self-Efficacy Scale
The General Self-Efficacy Scale (GSES) was compiled by Schwarzer et al. (1997). Z. J. Zhang (2005) translated the GSES into Chinese with high internal consistency (Cronbach's [alpha] = .75-.94). The scale consists of 10 items, and a 4-point Likert scale is used for scoring. The items are rated from 1 (completely wrong) to 4 (absolutely right). The sum of the scores of all items is the total score for self-efficacy, with higher scores indicating higher levels of self-efficacy. In this study, the overall Cronbach's [alpha] for the scale was .88, test-retest reliability was .93, and split-half reliability was .85.
Achievement Motive Scale
The Chinese version of the Achievement Motive Scale, originally developed by Nygard and Gjesme (1973), was used to measure the achievement motives of the participants (Ye & Hagtvet, 1992). The scale consists of 30 items and considers two factors: motive for success and motive to avoid failure. A 4-point Likert scale is used for scoring, and scores range from 1 (strongly disagree) to 4 (strongly agree), with higher scores for each factor indicating stronger motivation for that factor. In this study, the Cronbach's [alpha] for motive for success and motive to avoid failure were .87 and .89, respectively. Split-half reliability was .80, and test-retest reliability was .85.
Utrecht Work Engagement Scale
This scale was developed by Schaufeli et al. (2002) and revised and translated into Chinese by Y. W. Zhang and Gan (2005). The Chinese version of the work engagement scale has high internal consistency, with a Cronbach's [alpha] of .94. The total scale includes 16 items in three dimensions: vigor (six items), dedication (five items), and absorption (five items). All of the items are scored on a Likert scale from 0 (never) to 6 (always). The total score equals the sum of the items, with higher scores indicating higher levels of work engagement. In this study, the overall Cronbach's [alpha] for the scale was .89, and the [alpha] for each dimension was .84, .79, and .80, respectively. Test-retest reliability was .84, and split-half reliability was .83.
Procedures
Nurses who met the inclusion criteria were invited to participate in this study. The purpose and significance of this study were introduced, and written informed consent was obtained from all the participants before study enrollment. Before the formal survey, a pilot study on 50 nurses from two departments of the maternity and children's hospital was conducted. A questionnaire survey was administered to determine the readability and internal consistency of the four questionnaires. To increase the credibility of this survey, three research assistants were assigned to conduct face-to-face interviews. Questionnaires were distributed and collected during the nurses' normal weekly professional training session. All of the research assistants had received standardized training to improve interrater reliability, and the questionnaire was completed anonymously and collected onsite.
Validity and Reliability
The Chinese versions of the four instruments, including PES-NWI, GSES, Achievement Motive Scale, and Utrecht Work Engagement Scale, had all been adapted and published. All of the instruments used in this study showed high internal consistency, with Cronbach's [alpha] values of .86, .88, .88, and .89, respectively.
Data Analysis
IBM SPSS Statistics Version 17.0 (IBM Inc., Armonk, NY, USA) and IBM SPSS AMOS 23.0 (IBM, Inc., Armonk, NY, USA) were used for the data analysis. The general demographic information of the participants and their average scores for PNPE, achievement motivation, self-efficacy, and work engagement were used as the descriptive statistics. Stepwise multiple linear regression analysis was used to explore the factors influencing work engagement. Pearson's correlation analysis, hierarchical regression analyses, and structural equation modeling were conducted to explore the relationships between PNPE, achievement motivation, self-efficacy, and work engagement.
According to Schreiber (2008), to ensure the structural equation model achieves the appropriate degree of fit, all of the indicators must meet the following requirements: 1 < [chi]2/degrees of freedom (df) < 3, comparative fit index < .90, normed fit index < .90, standardized root mean square residual < .05, and root mean square error of approximation < .05.
Control Variables
Demographic variables, including gender, age, marital status, educational level, professional title, job tenure, and current position, were controlled in this study, as these characteristics may influence the dependent variable (Mukaihata et al., 2020; M. Zhang et al., 2021).
Ethical Considerations
The study was approved by the hospital ethics committee of the target hospitals (No. 2019071), and consent from the relevant departments in the four hospitals was obtained. In addition, all of the participants signed an informed consent.
Results
Demographic Data
Five hundred sixty questionnaires were distributed, and 515 valid questionnaires were returned, giving an effective response rate of 92%. In the valid data set, the average age was 28.25 (SD = 3.18) years, ranging from 21 to 54 years; most were female (93.2%) and married (77.1%). The proportion working in the surgical department was the highest (30.3%). Most (58.1%) held a college degree (graduated from a vocational school, focusing on professional skills learning). The largest proportion (37.9%) had worked for 4-10 years, and most (81.4%) were general nurses. Notably, most of the participants identified earning a living as their main purpose for working (41.9%). The details are shown in Table 1.
Descriptive Statistics
The participants perceived PNPE was at a medium level (mean = 2.41, SD = 0.58). Among the five dimensions of PNPE, the levels for nurse manager ability, leadership, and support of nurses were the highest (mean = 2.67, SD = 0.66), whereas the level of nurse participation in hospital affairs was the lowest (mean = 2.12, SD = 0.57). The score for achievement motivation was 0.26 +/- 0.08, indicating that the participants were slightly inclined toward achieving success. The self-efficacy of participants was at a medium-high level (mean = 2.81, SD = 0.84), with a medium-low level of work engagement (mean = 2.24, SD = 0.40). Among the three dimensions of work engagement, dedication earned the highest average score (mean = 2.47, SD = 0.42), whereas vigor earned the lowest (mean = 2.05, SD = 0.38). The details are shown in Table 2.
Descriptive Correlation
Correlations among the four variables were analyzed using Pearson's r correlations (Table 3). The results showed PNPE to correlate positively with work engagement, achievement motivation, and self-efficacy (r = .65, .59, and .49, respectively; p < .01), self-efficacy to correlate positively with work engagement and achievement motivation (r = .66 and .40, respectively; p < .01), and achievement to correlate positively with work engagement (r = .65, p < .01). Each dimension of the four variables showed different degrees of positive correlation (r = .39-.74, p < .01).
Tests of the Hypothesized Model
A multiple linear regression analysis was conducted to explore the effects of demographic characteristics, PNPE, self-efficacy, and achievement motivation on work engagement. The results showed that self-efficacy, the PNPE dimension of staffing and resource adequacy, and the achievement motivation dimension of motivation for success entered the regression model of work engagement, with standardized coefficients of .11, .15, and .32, respectively (p < .01), explaining 57.0% of the total variation (F = 80.51).
To test the mediating effect of self-efficacy and achievement motivation in the relationship between PNPE and work engagement, a hierarchical regression analysis was performed (Table 4). As shown in Models 1 and 2, after considering control variables, PNPE was found to affect work engagement and self-efficacy significantly ([beta] = .52 and .43, p < .01). As shown in Model 3, after introducing self-efficacy, the effect of PNPE on work engagement, although still significant ([beta] = .40, p < .01), was less than the effect in Model 1, indicating that self-efficacy plays a partial mediating role between PNPE and work engagement. In Models 4 and 5, after considering control variables, PNPE was shown to significantly affect achievement motivation ([beta] = .63, p < .01). Similarly, after the introduction of achievement motivation, the effect of PNPE on work engagement, although still significant ([beta] = .32, p < .01), was less than the effect in Model 1. These results support that achievement motivation plays a partial mediating role between PNPE and work engagement.
A structural equation model was established to verify the mediating effect of self-efficacy and achievement motivation. After modification, all of the indexes met the requirements ([chi]2/df = 1.256, comparative fit index = .986, normed fit index = .991, standardized root mean square residual = .021, and root mean square error of approximation = .035). The subsequent Sobel operator showed that self-efficacy and achievement motivation played a partial mediating role between PNPE and work engagement, with indirect effects of 30.87% (0.63 x 0.49) and 3.64% (0.28 x 0.13), respectively (Figure 1).
Discussion
Inadequate work engagement is one of the most difficult challenges faced in efforts to reduce employee turnover. Thus, this study was designed to explore the factors that impact work engagement in nurses. We implemented the model to test several hypotheses, and the model showed good fit with the sample. Significant and positive correlations were found among PNPE, self-efficacy, achievement motivation, and work engagement. In addition, the mediation of self-efficacy and achievement motivation in the relationship of PNPE and work engagement was also shown. Furthermore, the key role of internal resources in the JD-R model on work engagement was also confirmed.
Theoretical Implications
The average work engagement score in this study was 2.24 (SD = 0.40), which is significantly lower than that reported in the United States (Hetzel-Riggin et al., 2020) and Belgium (Van Bogaert et al., 2017). This may be related to the tension inherent in nurse-patient relationships and the heavy workload of nurses in China. Regarding the three dimensions of work engagement, dedication earned the highest score, followed by absorption and vigor. Employees with high dedication and low vigor are more likely to experience a sense of burnout or even leave their current position, especially under heavy workloads (Pericak et al., 2020). Therefore, improving the level of perceived vigor may be important to consider for nursing managers, especially as part of efforts to stabilize professional nursing teams in the postepidemic era (Wan et al., 2018).
In this study, PNPE was found to directly affect work engagement, with nursing staff and resource adequacy having the most significant impacts. These findings are consistent with earlier research results (Huang et al., 2021), reminding managers that adequate human resources and support services are critical to promoting work engagement in nurses and ensuring patient safety (Hetzel-Riggin et al., 2020). Beyond staff resources, other environmental factors such as structural empowerment, good cooperative relationships, and professional recognition effectively encourage nurses to achieve their professional goals (Al-Hammouri et al., 2021). When professional goals are successfully achieved, nurses will be more confident, increasing the likelihood of better engagement.
Beyond providing additional support for earlier findings, the most remarkable finding from this study is the mediating roles that self-efficacy and achievement motivation were found to play between PNPE and work engagement. The participants perceived supportive work environment, vigor, and dedication to work to be strengthened if they had higher self-confidence and motivation for success. These findings have not been verified in previous studies, but similar reports have confirmed achievement goals and goal processes to be catalysts for work engagement, especially in magnetic working environments (Bipp et al., 2021; Scharp et al., 2021). Moreover, the findings of this research further verified the important and positive relationship between PNPE and work engagement. The reason behind this relationship is that supported professional working environments are associated with increased internal obligations and improved work efficiency, as nurses have a higher emotional bond with organizations that they feel care about their needs and value their efforts (Cosme et al., 2021). PNPE, a variable that relates closely to self-efficacy (Trepanier et al., 2020), may be used to cultivate a sense of self-efficacy by providing necessary material resources, working conditions, and harmonious working relationships, which may then enhance work engagement (Wallin et al., 2021). Finally, the results of this study confirmed the JD-R model of Demerouti et al. (2001), in which job resources (including internal resources) were identified as the best indicator of organizational performance in employees who felt engaged in their work.
Relevance to Clinical Practice
To ensure nursing team stability and foster quality of care and mental health in nurses, nursing managers may want to take measures to improve nurses' work engagement to improve the dedication and motivation of their nursing workforce. Several implications for future clinical practice and policy arise from this study. First, a supportive working environment with sufficient human and material resources and a harmonious working atmosphere may be fostered to reduce nurse workloads and promote emotional well-being. In addition, nursing managers may take measures to improve systems governing the workplace, vacations, attendance, and welfare for clinical nurses to enhance their sense of professional benefit (Trepanier et al., 2020). In addition, nurses may be given more opportunities to participate in hospital affairs so that the actual problems of nurses can be reported to the managers in a timely manner. This can help nurses maintain enthusiasm for their work and be content with remaining in their current position (Cosme et al., 2021).
Second, nursing managers may also enhance nurses' sense of motivation for success by formulating talent training plans and establishing incentive mechanisms. These may include providing nurses with opportunities for further study at home and abroad, participating in national and provincial specialist nurse training, and participating in off-duty special English training (Mahdavi et al., 2021). In addition, nurses with excellent work performance may be recognized with appropriate rewards (Jedwab et al., 2021). Setting up special teaching and scientific research posts may also be used to stimulate nurses' desire for career success and promote their career development ambitions (Scharp et al., 2021).
Third, this research revealed that self-efficacy may mediate the relationship between work engagement and organizational performance. In addition, nursing professional self-efficacy varies according to specific area, task, and activity area and thus may increase performance motivation and result prediction (Kim et al., 2022). At present, the COVID-19 pandemic remains severe. Thus, in facing the high turnover rate and job burnout of nurses, effective strategies may be implemented to improve self-efficacy in nurses, including improving knowledge of the epidemic, carrying out continuing education and training, providing sufficient protective equipment, ensuring nurses' income and welfare at the policy level, reducing workload and the nurse-patient ratio, and providing psychological service support (Xiong et al., 2020). In addition, senior nurses may be empowered and provided with the opportunity to participate in department management, clinical teaching, organization, and coordination. In addition to giving junior nurses standardized training and professional clinical teaching, nursing managers may also encourage them. Giving affirmative verbal support can increase nurses' confidence in completing tasks, as self-efficacy indirectly affects nurses' professional ability, especially in the early stage of their careers (Falk-Brynhildsen et al., 2019).
Limitations
This study had several limitations. First, the participants were from four tertiary hospitals in Chengdu, and nurses from other regions and different hospital levels were not involved. Future studies should expand the sample size to investigate the situation among nurses in different regions and different levels of hospitals. Second, the cross-sectional design used in this study may not adequately explain the causal relationships among PNPE, self-efficacy, achievement motivation, and work engagement. Thus, longitudinal studies are suggested to verify the stability of the relationship between the four variables over time. Third, the multiple linear regression model in this study only explained 57% of the variance in work engagement, with 43% of the variance unexplored. Future studies should explore other critical factors to better elucidate the predictors of work engagement in nurses. Fourth, using means to compensate for the missing imputation reduced variance in the data, although we argue that imputation using the mean is acceptable because the proportion of missing data was low.
Conclusions
The findings of this study confirm positive correlations among PNPE, self-efficacy, achievement motivation, and work engagement. Our findings highlight the importance of PNPE in increasing work engagement in nurses. In addition, PNPE can enhance work engagement through the mediation of self-efficacy and achievement motivation. Furthermore, our research supports Demerouti's theory of JD-R in Chinese nurses and shows that the internal resources in the JD-R model play a key role in improving nurses' work engagement. In the current era of chronic nursing manpower shortages, nursing managers and administrators should make every effort to ensure nurses are better engaged in their work. Effective strategies such as providing a supportive work environment and improving nurses' perceived self-efficacy and motivation for success should be implemented to improve nurses' work engagement to reduce turnover rates.
Acknowledgments
This study was supported by the Science and Technology Project of Health Planning Committee of Sichuan (No. 20PJ083). The authors gratefully acknowledge the hospital leaders who provided us with the survey site, the 515 nurses who provided us with valuable data, and the experts who provided guidance and suggestions for this study.
Author Contributions
Study conception and design: YH, XD
Data collection: XD, YH, JHR, YLT
Data analysis and interpretation: XD, YLH
Drafting of the article: XD
Critical revision of the article: JHR, YLH
References