Regarding the subject types that applied flipped learning, practical subjects were the highest, with nine studies (50%), followed by seven theoretical subjects (38.9%) and two theory and practical subjects (11.1%). The theoretical subjects were critical thinking, nursing process, pathophysiology, health assessment, and patient safety, and the practical subjects were simulation practice, basic nursing practice, and clinical nursing practice.

Among the analysis papers, when applying flipped learning in practical subjects, nursing techniques cannot be directly performed. Thus, the methods and procedures of nursing techniques are repeatedly learned through audio-visual data [11]. Video content was used [19] or developed and applied by the instructor [31]. As the learning experience provided by the medium is different, the instructors set a clear goal through flipped learning, and the curiosity and motivation of learners were met.

As a result of the meta-analysis of flipped learning studies applied to 18 studies, the overall average effect size was 0.68, corresponding to the median effect size. This is similar to the study showing the median effect size of 0.58 as the overall average effect size of the learning effects of domestic flipped learning [40] and the study showing a median effect size of 0.59 as the effect size of flipped learning on domestic college students [41]. It was confirmed that flipped learning was more effective than traditional lecture-style classes when applied to nursing education.

As a result of comparing the effect sizes of the flipped learning outcome variables in this study, they were found in this order of critical thinking ability, learning satisfaction, clinical competence, and self-direction.

The critical thinking ability had a Hedges’ g of 0.87, showing a large effect size and a high level of heterogeneity. In five studies, the experimental group to which flipped learning was applied showed improved critical thinking ability compared to the control group. It can be predicted that flipped learning, which allows students to ask questions and solve problems on their own through prior learning and to improve critical thinking skills through discussion with other students during class in the classroom [42], is effective in nursing education. Additionally, a previous study [19] showed that although it is possible to acquire knowledge and skills, there is a limit to critical thinking. Instructors must grasp the learner’s disposition, attitude, and learning strategy and find and search for information rather than memorize knowledge; based on this, it is necessary to develop a running program.

As a result of analyzing the effect of flipped learning on learning satisfaction, the intermediate effect size was found to be Hedges’ g = 0.79. When learning flipped learning, information was provided to students, such as videos, animations, and images of clinical cases, inducing interest and resulting in positive responses. Satisfaction was high, as this allowed flexibility to learn at a desired speed and time [43,44]. However, there have also been studies with low learning satisfaction due to tasks assigned from prior learning during flipped learning, online environmental problems for learning, and adaptation to new teaching methods [8]. The instructor should consider the learner’s learning environment when developing flipped learning activities. It is necessary to consider avoiding a learning gap, such as understanding the infrastructure for watching videos and prior learning, and it is necessary to analyze the learning conditions in detail per the learning goal. In other words, it is necessary to promote understanding of learning by providing students with a plan for the learning content and learning method of flipped learning in advance so that they can familiarize themselves with the content to be learned. Additionally, the learner’s learning process was constantly monitored. A strategy for linking the content of prior learning and offline activities is needed by providing feedback on prior learning in the classroom.

As a result of analyzing whether flipped learning is more effective than traditional methods in improving nursing students’ clinical nursing skills, the effect size of clinical competence had a Hedges’ g of 0.53, showing a medium-sized effect. This confirmed that learning the procedure and techniques through videos was effective [45], and it was also confirmed by another study [46] that the clinical performance was improved by flipped learning in clinical practice. Nursing is a practical study. Direct nursing skills and repetitive practice are required to acquire and improve such skills. However, it is difficult to obtain qualitative improvement because of the inability to perform direct skills during flipped learning. When flipped learning is applied in practical classes, nursing skills and nursing theories are learned based on evidence, and in classroom sessions, the contents of prior learning can be directly performed. Additionally, it effectively improves students’ nursing skills through immediate feedback from instructors [47]. Factors for achieving clinical performance include interpersonal relationships and communication, nursing process, critical thinking, nursing intervention, creative thinking, basic nursing, and problem-solving ability [48]. These are improved by applying flipped learning to the subject in the corresponding domain, helping them to effectively perform the clinical nursing skills corresponding to the detailed elements.

In this study, the effect size of self-directedness was small (Hedges’ g = 0.37). The most important aspect of flipped learning is to increase the degree of self-directedness, and in many research results, self-directedness was improved through flipped learning [49,50]. Learners watched video lectures on pre-learning to familiarize themselves with the learning content, and the activities in the classroom were focused on learners. Notably, the self-directedness is improved due to the increased sense of responsibility and activeness in all learning processes [51]. Self-directedness is an important variable affecting learning outcomes, such as learning motivation, academic achievement, and satisfaction [52]. Through flipped learning, the instructors foster the learner’s learning ability and act as facilitators such that learners can have flexibility and develop lifelong learning habits for self-directedness [53]. Accordingly, when the learner’s characteristics and teaching methods are matched, self-directedness is achieved successfully. When designing a flipped learning curriculum, it is necessary to develop educational methods to improve self-directedness ability by focusing on learner-centered education.

Other variables related to the subject type and pre-learning method were the modulating variables that explained the difference in effect size. As a result of meta-ANOVA using the subject type as the moderator variable, the following were practical subjects, theory and practice mixed design subjects, and theory subjects.These results showed a significant difference in the flipped learning effect according to the subject type (Q = 13.59, p ≤ 0.001), and it was confirmed that the effect of a flipped learning class was higher in practical subjects. In a practical subject, flipped learning helps one experience knowledge integrated with observation and experience [12]. The interaction between the instructor and students increases, and the nursing skills gradually improve [8]. Studies have confirmed this effect. Additionally, the effect size value was calculated by classifying the learning methods into video method (15 episodes) and the method where video and lecture books were given (five episodes) simultaneously, indicating that the learning by the video method was higher but not statistically significant (Q = 1.22, p = 0.269). This could be because when the video and lecture book were given simultaneously, the number of assignments to be learned increased, consequently increasing the learning burden, and the lack of time and grade were not reflected. It is necessary for the instructor to explain in advance how the pre-learning videos are related to the lecture contents in order for the students to plan an appropriate amount of pre-study.