Abstract
This study investigated young children’s computational thinking (CT) development by integrating ScratchJr into a programming curriculum. Twelve third graders (six males and six females) voluntarily participated in an experiment-based computer class conducted at a public elementary school in Taiwan. This study adopted a case study methodology to investigate research questions in one specific case (8-week CT educational training). A one-group quasi-experimental pretest and posttest design with the support of qualitative observation was used to examine four research topics: CT competence progress, programming behaviors in a CT framework, factors influencing CT competence, and learning responses to CT training. The quantitative results indicated that students immersing in weekly programming projects significantly improved in terms of their CT competence, which was mostly retained 1 month after completion of the class. The programming behaviors indicated that students’ CT concepts (sequence, event, and parallelism) and practice (testing and debugging as well as reusing and remixing) significantly improved. Moreover, parents’ active involvement in take-home assignments influenced students’ long-term CT competence retention. The qualitative results indicated that students enjoyed using tablet computers to learn ScratchJr programming and demonstrated various leaning behaviors in a three-stage instructional design model.
Keywords
Introduction
ScratchJr is a newly developed visual programming language specifically designed for young children (under 8 years of age) to foster basic computational thinking (CT) competence (Strawhacker, Lee, & Bers, 2018). This programming tool (as an application) installed on tablet computers is a fundamental version of Scratch (Resnick et al., 2009). Scratch and ScratchJr share similar coding learning environments; however, ScratchJr does not include some advanced features such as variable creation and math computing. Although Falloon (2016) and Strawhacker et al. (2018) have demonstrated some learning benefits of ScratchJr for CT instruction, no scientific evidence regarding the effect of integrating ScratchJr into regular classes, particularly for CT competence development, is available.
This study reports findings regarding the use of ScratchJr for CT instruction in a computer class where elementary school students engaged in various programming activities over a single semester. A simplified version of the CT framework developed by Brennan and Resnick (2012) was used to document young children’s programming learning behaviors for further analysis. Instead of using large quantitative data for learning generalization, this study analyzed one case scenario where 12 third graders voluntarily participated in a semester-long educational experiment. The purpose of this study was to determine the instructional effectiveness of incorporating ScratchJr into a programming curriculum for elementary school students. Specifically, the four research objectives were to answer the following questions: RQ1: What CT competence progress did the students make after one semester of instruction? RQ2: Based on a single CT framework, what did the students’ programming learning behaviors look like? RQ3: What potential background information (e.g., gender) influenced the students’ CT competence? RQ4: What were young children’s learning responses to ScratchJr programming?
Educational Importance of CT Instruction
In her seminal paper, Wing (2006) defined CT as “solving problems, designing systems, and understanding human behavior by drawing on concepts fundamental to computer science” (p. 33). Wing (2008) further articulated that CT shares general analytical characteristics with mathematical thinking, engineering thinking, and scientific thinking. Since then, although discussions centered on defining CT have been controversial (e.g., Korkmaz, Cakir, & Ozden, 2017), the common core idea of CT training in schools is to empower students to think like a computer scientist or engineer and subsequently engage in a series of problem-solving learning tasks such as problem decomposition and pattern recognition (Barr & Stephenson, 2011).
In recent years, because of potential educational benefits, CT has been considered a required skill for digital citizens at several educational organizations. For example, the International Society for Technology in Education (2018) has incorporated CT into one of its learning standards, thereby forcing students to become computational thinkers for development of problem-solving strategies in a digital society. To follow this educational trend, countries worldwide have begun to promote coding as a CT training method in K-12 learning environments (e.g., micro:bit coding in U.K. schools; Schmidt, 2016). However, according to an educational technology report (The Horizon Report, 2017), considerable effort must be made by educators in developing innovative curricula when embracing coding for CT instruction.
Hsu, Chang, and Hung (2018) conducted a meta-analysis of CT studies from 2006 to 2017 and reported that many school teachers had adopted visual programming languages as coding tools for CT instruction. Through a systematic literature review, Lockwood and Mooney (2017) identified a similar trend involving visual programming languages; however, they reported that additional studies regarding CT instructional design are urgently needed. After an in-depth analysis of intervention studies, Lye and Koh (2014) found that all previous CT research focusing on visual programming languages had been implemented in after-school activities and suggested that future CT studies must investigate learning topics in naturalistic classroom settings. To respond to these research challenges, this study mainly used one visual programming language to deliver CT instruction in a regular computer class with a new instructional design approach at an elementary school.
CT Instruction Using Visual Programming Languages
Using visual programming languages to develop students’ CT skills is reportedly an effective learning strategy in elementary education (The Horizon Report, 2017). According to varied teaching aids, the methods for delivering CT instruction can be grouped into three categories: instruction with programming language only, instruction with programming language combined with educational robotics, and instruction with programming language combined with electronic devices. The first category focuses on CT instruction only and involves use of visual programming languages without the aid of any technological hardware. For example, Saez-Lopez, Roman-Gonzalez, and Vazquez-Cano (2016) evaluated the use of Scratch programming in an elementary school and reported that students improved their CT skills in problem-based learning activities. The second category advances students’ learning experiences through a combination of visual programming languages and educational robotics. For example, in Chou (2018a), elementary school students used Blockly programming to control mini robots. Direct qualitative observations revealed that programming design may foster students’ CT competence. The third category is similar to the second category but involves electronic devices rather than educational robotics. For instance, Chou (2018c) examined drone use by integrating Tynker programming in an after-school program and observed that elementary school students’ sequencing skills (one component of CT skills) were significantly enhanced. In this study, the first category (instruction with programming language only) was adopted to answer the research questions.
Although previous studies regarding varied CT instruction methods have yielded positive learning outcomes, whether students’ proficiency in CT skills covers problem-solving competencies that are transferable to other domains remains questionable (Millwood, Walsh, & Hooper, 2018). In the 1980s, use of the BASIC and LOGO programming languages for developing CT skills was heavily discussed. Pea and Kurland (1984) argued that the learning to code (CT skills) effects on wider thinking (knowledge transfer) still requires support from scientific evidence. Mayer, Dyck, and Vilberg (1986) contended that “there is no convincing evidence that learning a program (CT skills) enhances students’ general intellectual ability” (p. 609). They further suggested that learning to program benefits only students’ thinking skills directly related to programming languages already learned. However, in recent years, with the advent of visual programming languages, some studies have yielded promising results. In Lindh and Holgersson (2009), 1-year CT training through Lego robotics programming improved some elementary school students’ logical-thinking skills. Chou (2018b) reported that one-semester CT training through Arduino-based robotics programming may enhance elementary school students’ overall problem-solving skills. This study focused on students’ cognitive-thinking skills (i.e., CT skills) identified in ScratchJr programming learning rather than knowledge transfer to other subjects.
CT Framework and Instructional Model
Using Scratch programming as an instructional example, Brennan and Resnick (2012) developed a CT framework with three components, namely CT concepts, CT practice, and CT perspectives. This framework has been widely used to interpret young children’s programming works (Lye & Koh, 2014). In Brennan and Resnick’s framework, CT concepts refer to the fundamental concepts that students may learn in the coding process. These concepts include sequences, events, parallelism, conditionals, operators, and data. CT practice focuses on strategies that students use for coding and involves being incremental and iterative, testing and debugging, reusing and remixing, and abstracting and modularizing. CT perspectives are students’ “understandings of themselves, their relationships to others, and the technological world around them” (p. 10) when building codes. CT perspectives include expressing, connecting, and questioning. In this study, a simplified version of Brennan and Resnick’s CT framework was adopted to evaluate students’ programming behaviors because of the limited features in ScratchJr and the relatively low cognitive development of young children.
To meet instructional needs, previous studies have developed various models to deliver CT instruction to elementary school students. In Lee et al. (2011), the use–modify–create model was used to efficiently impart CT concepts to young children. The use concept involves borrowing someone’s idea. In the modify stage, students modify someone’s coding patterns, and then they subsequently develop a new CT project in the create stage. To follow engineering design principles, Chou (2018b) integrated a predesign, in-design, and postdesign model into a robot-programming curriculum. The predesign and in-design stages are similar to the use and modify stages in the model of Lee et al. The postdesign stage enables students to review and self-reflect on their CT projects. Chou (2018c) proposed a three-stage learning progression model (copy–Tynker–create) for a drone-programming curriculum. This model contains the necessary elements of the model of Lee et al. and differs only in terms of stage titles. This study is based on the model of Chou (2018c) and describes a new three-stage model to fit curriculum requirements.
CT Competence Measurement and Factors Influencing CT Competence
Various achievement tests have been designed to represent students’ CT competence. Many such tests solicit students’ problem-solving skills through well-structured programming questions that cover CT concepts and practice. Saez-Lopez et al. (2016) developed a visual block creative computing test to assess elementary students’ CT competence after the students had received Scratch instruction. In Chou (2018b), an achievement test from a national programming competition was used to measure elementary school students’ understanding of Scratch programming. Strawhacker et al. (2018) devised a battery of video-based programming tests that differed from traditional paper-based tests to assess young children’s CT competence after they had completed ScratchJr training. These tests require students to view programming questions in video clips and then provide answers on a structured answer sheet. This study employed the tests of Strawhacker et al. to observe students’ CT progress in a computer class.
Few related studies have analyzed the factors influencing young children’s CT competence in a programming class. Strawhacker et al. (2018) reported that different teaching styles affected students’ acquisition of programming knowledge in different manners. Chou (2018c) indicated that gender influenced young children’s programming patterns. However, findings from Longi (2016) regarding college students’ competence in learning programming may provide insight regarding the potential factors influencing CT competence. Through a systematic literature review, Longi summarized that two major factors, namely students’ background information and psychological characteristics, may predict students’ learning performance in programming courses. Students’ background information includes gender, prior programming learning experiences, and math skills. Psychological characteristics include any valid psychological measurements used to assess students’ learning styles, such as self-efficacy. In addition to the aforementioned two factors, Akinola and Nosiru (2014) found that lecturers’ teaching styles and attitudes played key roles in students’ programming performance. In this study, only background information was collected for further analysis; this information included that regarding gender, prior programming learning experiences, math skills, the assigned instructional group, and extent of parental involvement.
Research Methods
Research Design
Because the study focused on one specific case (8-week CT educational training) in school (Creswell, 2007), a case study methodology was adopted to investigate the research questions. According to Yin (2003), case study research might contain quantitative and qualitative elements. In this study, a one-group quasi-experimental pretest and posttest design with the support of qualitative observation was used to examine four research topics: (a) CT competence progress, (b) programming behaviors in a CT framework, (c) factors influencing CT competence, and (d) learning responses to CT training. Prior to the experiment, students were asked to complete a CT competence test (pretest) to assess their prior programming learning experiences. Subsequently, to facilitate the experimental process, a 2-week programming orientation course was conducted for the students to enable them to comprehend the fundamental knowledge of the visual programming language (i.e., the ScratchJr platform and programming blocks). During the 8-week experiment, the students had to complete eight CT projects in class as well as take-home written assignments. Upon completion of the experiment, the students received a CT competence posttest. The same CT competence test with different item numbers (delayed posttest) was administered to the students 4 weeks after the posttest had been completed. Figure 1 illustrates the research design of this study.
Research design of this study. CT = computational thinking.
Research Participants
The principal researcher collaborated with a public elementary school in Taiwan that was attempting to promote programming learning among young children by creating an experiment-based computer class. Two students were randomly selected for this study from each of the six third-grade classes at the school. Thus, the class included 12 third graders (six males and six females). A small class was recruited because several programming behaviors of the students needed to be documented by the instructor. This semester-long study was implemented in a regular classroom, and the 12 students were randomly divided into three learning groups of equal-gender status. At the beginning of this study, none of the students had programming experience, and all were aged less than 8 years. Moreover, no tablet computers with ScratchJr were provided at the participants’ houses. Because one male student dropped out of the class during the semester, only 11 data sets were used for further analysis. Figure 2 depicts the learning environment in the computer class.
A student learning to program in the classroom.
Research Instrument
ScratchJr on the tablet computer
In the weekly computer class, the students used ScratchJr to engage in CT learning activities. Each student was equipped with one small tablet computer (iPad mini). Students completed programming projects individually. Four students (two males and two females) formed the learning group. After the class, these students’ programming works were automatically saved on the tablet computers as weekly learning evidence.
CT competence test
The learning achievement test developed by Strawhacker et al. (2018) was used to measure the students’ CT competence. The test contains four categories: fixing the program, circling the blocks, matching the program, and reverse engineering. The first three categories involve multiple-choice questions, whereas the reverse engineering category requires the student to submit open responses. Irrespective of the type of question, each test item is accompanied by one short video clip that demonstrates a programming debugging process. This study adopted only the multiple-choice test items to achieve objective test scores. The score range of the test was 0 to 9. When the instructor administered the test, students were to carefully observe the video clips and circle the correct programming blocks printed on the paper. The high reliability and validity of the test is reported in Strawhacker et al.
Take-home assignments
In this study, weekly take-home assignments were developed for the students. The learning content was consistent with what students had learned in class. Each assignment was a written assignment with no requirement for ScratchJr use. However, one question in the assignment needed to be answered after an instructional video had been viewed. Figure 3 illustrates one of the weekly assignments.
Example of a take-home assignment.
Learning observation document
CT Concepts in the Learning Portfolio Document.
CT Practice in the Learning Portfolio Document.
Active Learning in the Learning Portfolio Document.
Students’ background information
Students’ Background Information.
Observation documents
The principal researcher conducted field observations to document student learning in class. Weekly observations were recorded in a journal. Moreover, the instructor summarized the weekly reflection notes after classes.
Instructional Design
Various simple and complex CT projects were developed for the educational experiments (see Appendix A). Only one instructor taught the weekly classes, each of which was scheduled as a 2-hour learning session (including a 20-minute break). A three-stage instructional model (Figure 4) was used to facilitate the students’ learning progress. In the review stage (approximately 20 minutes), the students discussed their take-home assignment. In the copy stage (approximately 40 minutes), the instructor imparted the project requirement and some programming skills. Subsequently, the students practiced programming examples from learning materials. In the modify stage (approximately 40 minutes), the students modified the programming examples by adding as many of their own ideas as possible. They were encouraged to incorporate all the CT concepts (sequence, loops, event, and parallelism) into their projects. During project development, the instructor observed the students’ performance by walking around the classroom and assisted the students when learning problems occurred.
Three-stage instructional model.
Data Analysis
Descriptive statistics, the t test, a one-way analysis of variance (ANOVA), Spearman correlation analysis, and partial correlation analysis were used to investigate three types of quantitative data: CT competence progress, coding learning behaviors, and factors influencing CT competence. The students’ responses were summarized in a qualitative format through the categorization of content analysis (Neuendorf, 2002). Moreover, a data triangulation method (Patton, 2002) was employed to confirm data consistency among the students’ levels of programming engagement, the instructor’s class observations, and the researcher’s observations (Figure 5).
Data triangulation in this study.
Results and Discussion
CT Competence Progress
Results of the t Test.
Pretest (M = 1, SD = 0.77); posttest (M = 7.5, SD = 1.11).
Delayed posttest (M = 6.95, SD = 1.33).
*p < .05. **p < .01.
Programming Learning Behaviors
Descriptive Statistics and t Test Results for the CT Concepts and Practice.
*p < .05. **p < .01.
The students’ weekly progress in the CT concepts and practice is illustrated in Figures 6 and 7. The findings indicated that the students’ proficiency improved steadily for the sequence (CT1) concept. The students’ proficiency for the loops (CT2), event (CT3), and parallelism (CT4) concepts fluctuated considerably; however, high proficiency was achieved for these three concepts in the final 2 weeks of class. Although the students’ testing and debugging (CTPR1) and reusing and remixing (CTPR2) behaviors also fluctuated considerably, their weekly performance surpassed the upper-intermediate threshold (4).
Learning progress of the CT concepts. Learning progress of the CT practice.

Results of Spearman Correlation Analysis.
*p < .05. **p < .01.
Factors Influencing CT Competence
Results of the One-Way ANOVA for the Posttest.
SS = Sum of Squares MS = Mean Sum of Squares
Results of the One-Way ANOVA for the Delayed Posttest.
A (frequent involvement): M = 7.9, SD = 1.14; B (less involvement): M = 6.17, SD = 0.93. SS = Sum of Squares). MS = Mean Sum of Squares
Learning Responses to ScratchJr Programming
Results of Partial Correlation Analysis for the Posttest.
Results of Partial Correlation Analysis for the Delayed Posttest.
Observation Results From the Instructor and Researcher.
CT = computational thinking.
Regarding the information in Table 12, nine qualitative categories can be summarized into four themes: regular learning behaviors (group learning and learning focus), technology use (programming language and tablet computer), instructional model (review, copy, and modify stages), and CT learning behaviors (CT concepts and practice). In the first theme, although some students often lacked concentration in class, most of students exhibited a peer support for project development. The second theme states that most of students enjoyed using ScratchJr. in their tablet computers. In the third theme, a learning problem appeared in the review stage where several students disliked assignment discussion because no technological tools were used in the review stage. Few learning problems were identified in the copy and modify stages. However, continuous encouragement from the instructor was needed for a better programming project in the modify stage. The fourth theme demonstrates how students applied CT concepts and practice into their project development. Students could put CT concepts into practice, particularly for sequence, event and parallelism, but they disliked using loops blocks to build their projects. As for CT practice, most of students showed their active engagement in programming testing and debugging.
Overall Discussion
Response to RQ1
After the 2-week programming orientation course, the students began to incorporate what they had learned into various theme-based projects. The quantitative findings indicated that weekly ScratchJr training significantly improved the students’ CT competence. Thus, with the aid of the 2-week orientation course, the 8-week CT project training course efficiently fostered young children’s CT competence. These results are supported by those of Saez-Lopez et al. (2016) and Chou (2018b). In Saez-Lopez et al. (2016), elementary school students engaging in Scratch activities exhibited significant improvement on a programming (or CT) knowledge test. Moreover, in Chou (2018b), significant learning progress was identified on a Scratch achievement (or CT) test after elementary school students had immersed themselves in weekly educational robotics programming classes. However, 1 month after completion of the experiment, although students’ learning retention of CT knowledge had remained at an acceptance level, their CT competence had significantly worsened. A possible explanation was that a small sample size and small score range of the test led to the statistical significance.
Response to RQ2
During the 8-week CT project training course in this study, the students demonstrated diverse programming learning patterns for CT concepts. From a weekly progress perspective, the students exhibited higher competence in all the CT concepts (sequence, loops, event, and parallelism) in the final week of training than in the previous weeks, even though their competence in the CT concepts had fluctuated considerably over the preceding 7 weeks. Inferential statistics revealed that the students had improved significantly in all the CT concepts (except for loops). A possible reason for the weakness in the loops concept was identified in the instructor’s notes, which indicated that the students had not liked to loops blocks. This finding was in agreement with an observation of Chou (2018a, 2018c), that elementary school students had preferred not using loops blocks to design their programming works. One finding of this study was that most of the CT concepts (sequence, loops, and event) were significantly related to project difficulty. When the project difficulty increased, the students’ CT concepts sometimes improved; a reasonable explanation behind this phenomenon is that a more difficult project may promote the idea of using additional CT concepts.
The learning patterns of CT practice differed from those of CT concepts. The students’ weekly CT practice (testing and debugging as well as reusing and remixing) fluctuated considerably and was unrelated to project difficulty; however, the weekly CT practice remained at an upper-intermediate level from week to week. In addition, the inferential statistics indicated that the 8-week CT project training course significantly enhanced the students’ CT practice. These findings can be attributed to two factors, namely learning support provided by peers and the instructor and the learning process in the instructional design model. First, the qualitative data indicated that the students and instructor had formed a strong support network where the students were able to seek help during programming development. Such learning scaffolding (Donohue, 2015; Jonassen, 1999) indirectly strengthened the students’ willingness for programming testing and debugging. Second, the second stage (copy) in the instructional design model enabled the students to practice programming examples and further increase their understanding of reusing and remixing, which was a required element in the final stage (modify) of the instructional design model.
Response to RQ3
The results of the CT competence pretest indicated that the students had little programming knowledge upon their enrolment in the computer class. The starting points of programming learning for all students were almost the same. After the 8-week CT project training course, the inferential statistics indicated that the collected background information (instructional group, gender, extent of parental involvement, and math skills) did not influence the students’ CT competence. Because this study focused on elementary school students, the findings differed considerably from those of an adult learning study that identified effects of background information (e.g., gender, math skills) on programming (CT) competence (Longi, 2016). However, 1 month after project completion, the extent of parental involvement exerted a strong influence on the students’ CT competence. Thus, frequent parental involvement in assignments may strengthen students’ learning retention of CT knowledge. This result was interpreted through the qualitative data, which also indicated that students may pay more attention to assignments when in their parents’ company, and frequent parental involvement might reinforce students’ CT knowledge recall. Similar to background information, the students’ in-class learning behaviors (CT concepts, CT practice, and active learning) were also not related to their CT competence. A possible reason for this outcome is that the students’ in-class learning behaviors reflected only their learning status in weekly projects and did not indicate their CT competence.
Response to RQ4
The qualitative learning responses from the researcher and instructor indicated learning advantages of ScratchJr (software) and the tablet computers (hardware) in the computer class. Although a few students expressed displeasure regarding the limited range of features, the game-based interface of the ScratchJr platform enabled the students to easily explore potential programming features (Falloon, 2016; Strawhacker et al., 2018). Furthermore, the mobility of the tablet computers empowered the students to conduct their programming and discuss programming problems with their classmates (Chou & Feng, 2019). Regarding the instructional design model, the qualitative data indicated that the students seemed to lose learning interest in the first stage (review) because the review activity of take-home assignments was similar to the traditional educational format. After progressing to the second stage (copy), the students did not face any learning problems in practicing programming examples. However, in the final stage (modify), the students were well satisfied with their performance if the instructor did not prompt them to work further. Continual encouragement from the instructor was required for superior project development (Chou, 2018b).
Conclusion
Contributions of This Study
This study investigated how elementary school students used a visual programming language (ScratchJr) to develop their CT competence through various programming projects in an experiment-based computer class. The findings confirmed that an 8-week CT project training course significantly fostered young children’s CT competence. The students exhibited high retention of CT competence 1 month after completion of the programming curriculum. Furthermore, although different learning patterns appeared in weekly CT concepts and practice, the students’ overall CT concepts (except loops) and practice had significantly improved after programming project training. This study identified that the parent-involvement time in students’ assignment activities may play a key role in students’ retention of CT competence. In addition to the quantitative evidence, the qualitative findings proved that young children can enjoy using tablet computers to learn ScratchJr programming. The students exhibited various learning behaviors in the three-stage instructional design model. For example, several students did not pay attention to assignment discussion in the review stage; most of the students had no problems in copying the instructors’ programming examples in the copy stage; most of students need the instructor’s encouragement to add additional programming blocks in the modify stage.
Research Limitations and Suggestions for Future Studies
The results of the study may be difficult to generalize to other learning settings because the research design process had several limitations. First, this study recruited only a small number of students to minimize the teaching tasks of the instructor. Future studies may increase the number of students (e.g., 25) to further investigate the topic of this study. Second, this study focused on students’ programming learning progress during CT project development. Future studies may employ a content analysis approach to examine students’ programming works. Third, the proposed instructional design model forced the students to repeatedly modify programming examples. Further research could strive to determine whether encouraging students to develop new programming works benefits their learning. Fourth, the study only adopted one-group quasi-experimental pretest and posttest design. Future studies may set up a control group to provide a better research comparison. Fifth, the qualitative observation revealed that the take-home worksheets might demotivate student learning. Future studies may confirm the effect of the assignment on students’ CT competence development. Sixth, the study employed one specific learning achievement test (multiple-choice items) to measure students’ CT competences. Future studies may use or develop non-selected-response test items to assess young children’s CT competences. Different CT learning patterns may be obtained. Seventh, the parental involvement did have an effect on students’ CT competences in the study. To identify students’ intrinsic motivation, future studies may require students to complete worksheets before they go home. Finally, the collaborating elementary school in this study provided only third graders as participants; students’ ages may influence their cognitive development during programming training. Future studies could recruit children younger than those in this study for comparison of programming patterns based on age.
Instructional Implications
Because this study investigated the instructional effectiveness of ScratchJr integrated into a computer class in an elementary school, the findings may provide some practical suggestions for educators attempting to promote coding literacy among young children. First, learning interaction among peers may influence students’ debugging and testing abilities. Instructors could employ a range of collaborative learning strategies to facilitate students’ programming engagement. Second, classroom management problems such as students using other apps during computer classes may affect students’ learning focus. Instructors could design reward rubrics to prevent such problems. Finally, depending on the educational level of the students involved, the instructional design model proposed in this study could be modified to fit an expected course structure. For young children, instructors could remove the review process from the model to decrease students’ cognitive learning load.
Footnotes
Appendix A: Weekly CT Projects
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was funded by Ministry of Science and Technology in Taiwan [grant number: MOST108-2511-H-024 -006 -MY3].
