In the rapidly changing social environment influenced by the recent COVID-19 pandemic and the Fourth Industrial Revolution, educational methods that utilize diverse content are emerging. During the COVID-19 pandemic, most universities in Korea and worldwide interacted with students through online education instead of in traditional classroom settings [1]. This shift in educational modalities persists even after the pandemic. Information and communications technology (ICT) classes based on technologies frequently used by the younger generations, such as mobile phones, tablet PCs, and social networking services, have become prevalent [2]. The ability to accept and utilize these ICTs is referred to as "digital literacy" [3]. In recent times, digital literacy, a crucial competency for acquiring knowledge and information in modern society, is actively incorporated into university education using digital media-based learning methods [4].

The advancement and expansion of digital health have improved the quality of diagnosis and treatment; this has led digital literacy to become an essential component of medical and healthcare education and services [5]. In the nursing field, digital literacy is indispensable for accurately interpreting and managing diverse patient information while performing evidence-based nursing practice [6]. This is because the rapidly evolving clinical environment driven by technological advancements demands high-level skills for information utilization. The American Association of Colleges of Nursing recommends incorporating nursing informatics into the nursing curriculum [7]. This reflects American nursing colleges' proactive response to current societal demands for nursing competencies. In Korea, nursing education actively incorporates online content for learning [1], explores various educational methods, and incorporates various platforms such as Zoom to achieve learning outcomes [8]. To train future healthcare professionals to adapt well to the new digital environment, it is necessary to employ educational methods that enable nursing students to leverage their digital literacy in acquiring nursing expertise [9]. Recently, various teaching methods such as team-based learning and case-based learning have been utilized, but attention should be paid to flipped learning, which is relatively easy to utilize through digital literacy, is more flexible than team-based learning (TBL), can promote self-directed learning by increasing immersion in learning content [10], and supports academic-centered learning activities by enhancing conceptual understanding compared to case-based learning (CBL) [11]. Against this backdrop, flipped learning has garnered attention as an effective instructional strategy among various digital media-based learning methods, particularly for promoting self-directed learning and increasing student engagement in the classroom [12,13]. Often referred to as "inverted learning," flipped learning enables learners to acquire foundational knowledge through online pre-class activities and then engage in deeper learning during in-class discussions and problem-solving exercises. This approach is characterized by a flexible learning environment, a shift toward a learner-centered culture, the use of active learning strategies, and the implementation of professional teaching techniques [12]. By utilizing digital tools during the preparatory phase and encouraging active student participation during class, flipped learning facilitates the transition from teacher-centered to learner-centered instruction [12]. In this study, digital literacy was employed from the initial stages of instruction to maximize the effectiveness of flipped learning. Rather than simply using digital tools, digital literacy was conceptualized as a core individual competency that enhances learning outcomes. Digital literacy, in particular, is regarded as a concept that encompasses three sub-skills: the technical ability to search for and utilize digital content, the cognitive ability to evaluate and structure information, and the socioemotional ability to communicate and act ethically in online environments. These elements are essential to enhancing the effectiveness of flipped learning in nursing education. Moreover, while previous studies on flipped learning primarily relied on instructor-provided content [13-18], this study is distinguished by incorporating a pre-class learning process in which students independently search for and select digital resources. This change not only allowed students to apply their digital literacy but also offered a structurally different approach. Therefore, the "flipped learning utilizing digital literacy" in this study extends beyond the application of digital tools, representing a comprehensive instructional design that integrates learners' digital competencies throughout the learning process.

In nursing education, critical thinking and self-directed learning ability are essential competencies for enhancing problem-solving skills and professional growth in clinical settings [18]. Critical thinking is defined as a cognitive process in which learners make informed decisions and solve problems in complex situations [19], serving as a cornerstone of clinical judgment and evidence-based nursing practice [20]. Self-directed learning refers to an autonomous learning process in which learners set their own goals, select strategies, and evaluate outcomes [21], forming the foundation for continuous professional development and lifelong learning in rapidly changing clinical environments [22]. The Partnership for 21st Century Skills (P21) also identifies critical thinking as one of the core competencies for future professionals [23], underscoring the importance of educational strategies that foster these abilities in nursing students. Previous studies have shown that flipped learning positively impacts students' critical thinking and self-directed learning abilities, primarily through online pre-class learning and active in-class interaction [18]. Therefore, this study aims to evaluate the effects of flipped learning, with an emphasis on digital literacy, on these two core competencies in nursing students. Previous studies that examined the effects of flipped learning on critical thinking and self-directed learning mostly involved lower-year nursing students and were conducted as single-group experimental studies, only assessing the pre- and post-effects of education [13-17]. The duration of these studies varied from 3 to 7 weeks; however, the intervention periods were relatively short, limiting the ability to attribute the observed effects solely to the flipped learning method. Additionally, these studies did not consider the digital competencies of the students. In Korea, lower-year nursing students (freshmen and sophomores) typically study foundational subjects necessary for their major, while third-year students and above engage in clinical practice and begin to study major subjects in greater depth. Effective learning of these major subjects is crucial for enhancing nursing competencies post-graduation, highlighting the need for various approaches to improve learning outcomes. Therefore, this study aimed to identify the level of digital literacy among third-year nursing students and to verify the effects of flipped learning, utilizing digital literacy, on critical thinking and self-directed learning. The study's hypotheses are as follows:

This study examined the impact of digital literacy-based flipped learning methods on the critical thinking and self-directed learning abilities of Korean nursing students. The participants' average digital literacy score was 3.80∼3.81. This score was interpreted as relatively high, based on previous studies that reported similar levels and evaluated them as high among Korean [24] and Turkish [27] nursing students using comparable measurement tools. Similarly, prior research involving Turkish healthcare students, including nursing students, reported high digital literacy, similar to our study results [28]. Studies by Kim and Park [2,9], Kim [5], and Yoon [29] using various tools also reported high digital literacy among nursing students in South Korea. Internationally, high digital literacy has been reported among nursing students in Turkey [27], Australia [30], and the UAE [31]. Martzoukou's study found that nursing students indicated that younger students and freshmen had higher digital literacy than older and senior students [32]. Thus, it can be inferred that nursing students globally have high digital literacy capabilities. Consequently, it is essential for future nurses to continuously develop their ability to use evolving digital health technologies. Additionally, despite the variability in the number of items and the use of a 5-point Likert scale across different tools (Kim [2]; Kim [4]; Park [9]; Erdat et al.[27]; Yoon [29]; Lokmic-Tomkms [30]), the differences in tools did not affect the study outcomes. Unlike previous studies [13-18] that provided learning materials before class to encourage student participation, the intervention in this study-"flipped learning utilizing digital literacy" sought to differentiate itself by requiring students to search for learning materials independently using digital literacy skills. This change was intended to reflect a key feature of flipped learning, which enables students to construct knowledge more effectively by learning independently in any environment through complex and diverse learning activities and by providing richer opportunities for learning [12]. Our study findings did not support the first hypothesis, "The experimental group will have higher critical thinking scores than the control group," although there was some improvement in the experimental group's critical thinking. In contrast, a decrease in critical thinking scores was observed in the control group. These findings differ from those of previous studies that reported significant improvements in nursing students' critical thinking through flipped learning interventions [13-18]. Notably, while earlier studies implemented flipped learning for limited durations-four sessions over eight weeks [17], six weeks [14], ten weeks [15], and five sessions over 15 weeks [13,16]-this study applied flipped learning consistently over a full 13 week period, which is relatively uncommon. A previous meta-analysis of flipped learning [33] reported the largest effect sizes in interventions lasting seven to eight weeks. Compared to short-term interventions, continuous exposure to flipped learning may have led to cognitive fatigue, reduced concentration, or diminished intrinsic motivation. Additionally, during the flipped learning sessions in this study, students participated in group discussions composed of seven-eight members, which contrasts with previous studies that used smaller groups of two [15], four-five [13], or six [18] members. To maximize the effects of flipped learning, active interaction and the expression of individual opinions are essential [12], and thus, setting an appropriate group size is critical. The relatively large group size in this study may have limited individual participation opportunities or caused some students to adopt more passive roles. Indeed, small group settings have been reported to facilitate more active participation and feedback in flipped learning environments [34]. This increased participation suggests that the impact on critical thinking skills may vary depending on how the instructor designs the components of the class. Meanwhile, the decrease in critical thinking scores in the control group may suggest that traditional lecture-based instruction fails to stimulate learners' critical thinking adequately or that an emphasis on test-oriented, fragmented knowledge acquisition could hinder flexible thinking. Critical thinking is a high-level cognitive skill that is difficult to enhance through short-term instructional methods alone. It is influenced not only by teaching strategies but also by learners' cognitive engagement, interaction, the quality of feedback, and the complexity of tasks [19]. Therefore, in an era of information and diverse values, it is essential to develop educational programs that foster the habits and attitudes associated with critical thinking, which are vital for future nurses. The study findings supported the second hypothesis, "The experimental group will have higher self-directed learning scores than the control group". This aligns with the findings of Yang et al. [16], Kim [17], and Fan et al. [35], who reported improved self-directed learning abilities in nursing students through flipped learning. Flipped learning is not merely about providing pre-class content and delivering lectures in a one-way format; rather, it involves reviewing the content during class and engaging students through activities such as quizzes, questions, and discussions. In doing so, it encourages students to proactively study the content before class, thereby fostering self-directed learning. In this context, flipped learning can be regarded as an instructional method that enhances self-directed learning. Among the subdomains of self-directed learning, significant improvements were observed in learning strategies, learning activities, and evaluation. This improvement can be attributed to the structure of the flipped learning approach, which encouraged students to actively engage in class by searching for materials in advance and participating in quizzes and discussions. In contrast, the lack of significant changes in awareness and interpersonal skills might be explained by the relatively large group size used in this study, which may have limited deeper interaction among students, as previously discussed. Meanwhile, the control group showed a tendency for a decline in self-directed learning ability. This result can be interpreted as learners becoming accustomed to passively receiving information in traditional lecture-based classes, limiting their opportunities to plan or regulate their learning. Additionally, repetitive one-way delivery methods may reduce learning motivation, thereby weakening self-directed learning attitudes [18]. Therefore, further research is needed on the development of up-to-date clinical case-based content and various teaching methods to promote active participation among nursing students. This study is significant because it applied flipped learning using digital literacy to a core nursing theory course for third-year nursing students in South Korea, demonstrating its effectiveness in enhancing self-directed learning and the positive correlations between digital literacy and learning-related variables. This study did not differentiate between interventions based on individual digital literacy levels and only confirmed homogeneity between the experimental and control groups. Given the impact of digital literacy on self-directed learning, future research should explore interventions tailored to different levels of digital literacy. In addition, although the pre-learning videos were made available only through the LMS of the experimental group, there is a possibility that the experimental treatment may have unintentionally spread to the control group. As this could have influenced the study results, future studies should incorporate design considerations to block or control information sharing between groups.

This study applied a flipped learning approach in which students used digital literacy to engage in pre-online class learning and actively participate in class, rather than solely delivering content in a traditional lecture format. The study findings demonstrated that the flipped learning method was more effective than the conventional lecture format in enhancing self-directed learning. However, the findings also highlighted that critical thinking is not easily altered in the short term and require long-term observation and development. Furthermore, when selecting educational delivery methods and evaluating their effectiveness, it is important to consider both short-term effects, such as knowledge improvement, and long-term effects such as critical thinking enhancement. This approach ensured a comprehensive evaluation of educational interventions based on learners' digital literacy levels. Flipped learning utilizing digital literacy is expected to help nursing students adapt well to rapidly changing learning environments and improve learning-related competencies that will likely lead to improved patient care quality.