In March 2020, the World Health Organization declared COVID-19, also known as the coronavirus, a pandemic. Distance learning was proposed as an important educational paradigm to overcome the limitation of conventional face-to-face classes. As mutations of the coronavirus continue to develop, distance learning continues to be used for nursing education. It is essential to find more detailed and varying methods for distance learning, along with each method's effects. Distance learning is a form of education that uses the internet and web-connected communication tools as a strategy for the transfer of knowledge [1]. Words that refer to online classes have been used interchangeably with various terms such as online learning, online education, e-learning, and web-based instruction. However, as online and e-learning classes recently became active in general higher education institutions, as well as cyber universities, the terms have been unified into the catchall term of distance learning [2].

Distance learning can be divided into two modes: synchronous learning and asynchronous learning [3]. Synchronous learning is live, real-time (usually scheduled), facilitated instruction, and utilizes learning-oriented interaction. Asynchronous learning takes advantage of computer-mediated communication to achieve the promises of learning anytime, and anywhere [3].

When the learner's sense of presence in distance learning is improved, active learning activities increase, which can lead to positive learning outcomes such as improved academic achievement and satisfaction [4]. The sense of presence refers to being there in a virtual space [4]. Presence is the subjective experience of being in one place or environment, even when physically situated in another [5]. In the learning situation, presence can be divided into teaching presence and learning presence [6].

The perception of the external learning environment recognized by the learner in the learning process is the teaching presence, and the learning presence is the perception of one's inner self [4]. Teaching presence is how the learner feels about the instructor's consideration [7]. To realize meaningful and educationally significant learning effects, teaching presence designs and promotes learners' cognitive and social processes [6].

Learning presence refers to the learner's intrinsic awareness and means of cognitive and emotional perception during the learning process, along with their learning contents in specific situations [8]. If the learner's presence is improved in distance learning, positive learning outcomes can be derived [9].

Learning outcomes result from learners' acquisition of changes and development levels, knowledge, and technology that emerge from that learning [10]. Metrics for measuring learning outcomes in distance learning can be broadly divided into academic satisfaction, academic achievement, and learning persistence [11]. Learning satisfaction is an important indicator of whether learners' needs are met [12]. When new media and teaching methods are introduced, it will have a significant impact on whether learners will accept them in the future or not [13].

One of the most actively used measurement variables of learning outcomes has traditionally been academic achievement [14]. Academic achievement is related to the interaction between teachers and learners and their willingness to participate in learning in distance learning [15]. Distance learning is more likely to deviate from learning than conventional face-to-face classes. Hence, learning persistence, an action taken to continue learning, is a crucial evaluation method in measuring learning outcomes in online education [16].

As such, prior research has been conducted focusing on the sense of presence and learning outcomes in distance learning [14, 15, 16]. However, studies comparing distance learning differences according to delivery format were rare. Schoenfeld-Tacher and Dorman [17] reported that there was no difference in academic achievement according to a study targeting individuals studying veterinary medicine. Lin and Gao [18] found that active interaction is often stimulated through synchronous learning, while students can learn on their own pace in asynchronous learning in a study with Chinese university students. Challenges are also perceived in both formats, such as being distracted by classmates in synchronous learning or feeling social isolated in asynchronous learning.

Therefore, the purpose of the study was to explore the effects of the delivery format on teaching presence, learning presence, and learning outcomes and to identify the correlation among them in distance learning for nursing students during the COVID-19 pandemic in Korea. It is meaningful to have a foundation for building a post-coronavirus distance learning environment based on the most effective delivery format.

As face-to-face learning is no longer possible due to the COVID-19 outbreak, attention is being given distance learning globally. In Korea, a lot of confusion existed at the beginning of the semester. Most universities nationwide planned to run distance learning programs for the first semester of 2020 [25]. This study was carried out after the lockdown of universities took place as an emergency response to the COVID-19 pandemic. It aims to improve the quality of distance learning by identifying the differences between teaching presence, learning presence, and learning outcomes according to the delivery format. In synchronous learning, teaching presence (especially direct facilitation) and learning presence (especially emotional expression) had a higher statistical significance compared to asynchronous learning. However, in the learning outcomes, no statistically significant difference was observed.

There was a significant positive correlation between teaching presence, learning presence, and learning outcomes, and there was also a significant positive correlation between each subdomain. This supports the meta-analysis results, demonstrating that the higher the learner's presence level, the more positive the effect was on learning satisfaction and academic achievement in digital learning environments [4, 9]. The sense of presence in the distance learning environment had a positive effect on the learning outcomes. Based on this result, it can be suggested that learning outcomes can be improved if presence is improved in distance learning environments.

No statistically significant difference existed in the learning outcomes according to the delivery format (synchronous versus asynchronous learning). However, there was a statistically significant difference in the teaching presence and learning presence subdomains.

Based on the distance learning delivery format, the mean of teaching presence in synchronous learning was higher compared to asynchronous learning, but there was no statistically significant difference. In the subdomain of the teaching presence, a higher statistical significance was found for direct facilitation in synchronous learning. This is consistent with the results of the study, which mentioned that synchronous learning has the potential to facilitate learner-centered classes based on interactions [7]. In a study by Dzubinski [26], it was reported that feedback online and personal communication through e-mail, phone, and office visits improved the teaching presence in the asynchronous delivery format. This can be considered as an effective method for improving direct facilitation, which had lower statistical significance in this study for asynchronous learning.

The subdomains of instructional design and organization had higher statistical significance in asynchronous learning, but no statistically significant difference was observed. This is consistent with the results, which showed that the provision of asynchronous learning presented clear educational goals and increased the organic linkage between classes and the appropriate length of class [27].

In learning presence, the subdomain of emotional expression belonging to emotional presence had a higher statistical significance in synchronous learning. This resulted because synchronous learning can allow students to express feelings and opinions. In a study of Chinese university students, Lin, and Gao [18] stated that interaction is often stimulated in synchronous learning, while students can learn at their own pace in asynchronous learning environments. Challenges are also perceived in both delivery formats, such as being distracted by classmates in synchronous learning or feeling socially isolated in asynchronous learning. Kang et al. [19] reported that enhancing emotional presence in distance learning may improve learner satisfaction. For online instructors, it is challenging to understand the affective experiences of online learners. Instructors provide detailed examples under each theme and pay attention to students' affective domain, particularly in asynchronous learning [28]. Meanwhile, the subdomain of cognitive presence was higher in synchronous learning, but no statistically significant difference existed.

Learning satisfaction belonging to learning outcomes was higher in synchronous learning, but no statistically significant difference existed. This made a difference, described by Cooke et al. [29], that showed learning satisfaction in synchronous learning (live lecture) to be overwhelmingly higher compared to asynchronous learning (optional lecture capture) in a study targeting nursing students. Although it is a slightly different point of view, differing study results were seen on learning satisfaction in distance learning and campus-based learning. Additionally, Choi [26] reported that the evaluation of basic medical subjects conducted by distance learning for the 1st year medical students were better based on all scales, such as overall satisfaction, the organic linkage between classes, and appropriateness of class length, compared to the previous year of campus-based learning.

Among the learning outcomes, the only perceived achievement was higher in asynchronous learning, but no statistically significant difference was present. This supported the study's result that showed no difference in academic performance according to the delivery method in the Schoenfeld-Teacher and Dorman [17] study of veterinary college students.

Learning persistence was higher in synchronous learning, but there was no statistically significant difference. In a study focused on developing a tool to measure the continuity of online education for nursing students, Hart [30] found the following four constructs: connectedness, perceived stress and support, self-motivation, and goal attachment. It is thought that various approaches, including the results of this study, will be needed in future studies on learning continuity related to online nursing education.

The new normal era of post-coronavirus nursing education will combine distance learning and face-to-face learning, and synchronous learning and asynchronous will work harmoniously. At a time when the importance of distance learning is gaining more attention, this research is significant in that it has become a foundation for building a distance learning environment based on delivery format.

Distance learning is emerging due to the COVID-19 pandemic. In this study, we identified the presence and learning outcomes by dividing distance learning into synchronous and asynchronous learning. In asynchronous learning, teaching presence (especially direct facilitation) and learning presence (especially emotional expression) had a lower compared to synchronous learning. As the study results show, the difficulty in direct facilitation and emotional expression is a weakness of asynchronous learning. Therefore, it is necessary to add contact with nursing students and instructors and to help students express their emotions to improve presence in the asynchronous learning. It can be suggested that instructors and students can increase the presence via direct interaction, such as chatting and e-mail. There were significant positive correlations between teaching presence, learning presence, and learning outcomes. It can be suggested that learning outcomes can be improved if presence is improved in the distance learning environment. In order to increase the presence, it is worth considering the use of a distance learning platform. In the future it is necessary to identify whether various communication channels, feedback, and real-time course status confirmation through the distance learning platform can enhance learning outcomes.