A systematic review of health sciences students’ online learning during the COVID-19 pandemic

This study aims to analyse the effectiveness of distance learning during the COVID-19 pandemic among undergraduate health sciences students using systematic review. Online learning has been chosen as the best approach to continue offering education in this pandemic era. Method: The screening process was done using Scopus, ScienceDirect and PubMed based on the eligibility criteria. Out of 1486 studies, 1269 were screened. A total of 64 eligible studies obtained were included in the quantitative analysis. Results were categorized into i) student attitudes (perceptions/satisfactions/engagements), and ii) student learning outcomes, and compared to the Kirkpatrick model. Although facing difficulties, 50% of the studies was moderately satisfied with distance learning, while 36% was highly satisfied and 17% dissatisfied. Most studies (26%) reported flexibility in online learning. Internet issues (19%) and low interaction between learners and instructors (19%) were the most prevalent problems mentioned. Online education engages students better than traditional learning. The learning outcome was assessed using two categories: i) academic performance and ii) skill development. Most studies (72%) stated that online learning improves academic performance, 14% reported a drop, and 14% stated no effect, while an increase in clinical skills and communication skills were reported. Kirkpatrick evaluation revealed 80% of the studies obtained was evaluated at level 1 (reaction), 8% at level 2 (learning), 12% at level 3 (behaviour) and none at level 4 (results). Overall, this systematic review found that the online learning performed better than expected during COVID-19, but the data gained is insufficient to say it is beneficial when compared to other types of teaching approaches.


Background
A significant increase in the usage and acceptance of educational technology was already noticed by researchers in 2019, a year prior to the COVID-19 pandemic [1][2][3][4]. The use of suitable information and communications technology (ICT) in education is deemed critical as it can benefit all students [5]. Many researchers suggest that through a better understanding of the obstacles and aspirations of students, higher educational institutions may develop measures to help them continue getting the best education in the event of a pandemic that forces a switch from a traditional mode of learning (physical, face-to-face sessions) to a remote one [6].
One of the defining characteristics of online learning is that students can participate in the learning sessions at any time [7]. Although face-to-face learning remains the preferred way of delivery, the use of a blend of synchronous and asynchronous online learning has grown Open Access *Correspondence: abdah@upm.edu.my Abdull Mutalib et al. BMC Medical Education (2022) 22:524 in popularity in recent times [8]. Different persons and age groups respond to online learning in different ways. Challenges such as download faults, installation issues, login issues, audio and video issues, as well as lack of interaction between students and teachers remain some of the most pressing obstacles to this increasingly popular delivery method. On a similar note, some students believe that pre-recorded videos are the most effective way to conduct lessons during the pandemic [8].
Past studies have suggested that the outcome of distance / online learning is, at large, mixed. A study by Hurlbut (2018) reported that students perform better in physical classes compared to online ones [9]. This is further validated by Sintema [10], who reported that students' academic performance is significantly affected by their presence in physical classes, as in-person individual activities are essential for students to comprehend the subject matter [11]. Some researchers have also attempted to investigate the impacts of online learning on students' attitudes. Student engagement, satisfaction, and perceptions are examples of student attitudes that can be observed and determined [12]. As attitudes are subjective, evaluating an individual's or a group's attitudes is challenging and numerous factors must be considered in order to properly evaluate them. Observation, direct questions on their views about the subject, performance assessments, and observing the respondents' reaction on organized stimuli are approaches that can be used to gather data for attitudes [13].
Meanwhile, another group of researchers reported that students recorded better performances in a nonphysical learning setting. According to Heitmann et al. (2022), students who received non-bedside teaching performed better than those who attended physical classes [14]. In addition, Hannay and Newvine (2006) found that students that undergo web-based learning performed a lot better than those who received faceto-face education [15]. Some researchers have also discovered that the impact of online learning to students' performance is either not significant or negative in nature. Kemp & Grieve (2014) stated that no significant difference on test performance was noticed when they compare students studying in physical class to those learning online [16]. Others such as Mukhtar et al. (2022) reported that students' performance through online learning is expected to deteriorate due to problems with technology and lack of communications with instructors whenever the students face difficulties grasping the learning content. Students also stated that they had difficulty paying attention during lectures. Several instructors have reported misbehaving students during online assessments where these students referred to their lecture notes and searched the internet for solutions during the assessment, despite being told not to [17].
Despite having some evidence that online learning is as successful as conventional methods of learning, there is relatively little research concerning which specific method works (specifically within the domain of Health Sciences) and how online learning improves teaching and learning -especially during the COVID-19 pandemic. Considering the learning styles, pedagogical designs, and students' expectations unique to the Health Sciences, integrating online learning into Health Science education may be a particularly tricky endeavor. It is for this reason that this systematic review aims to analyze recent publications and research on online learning during COVID-19 pandemic among Health Sciences students to extract valuable key learnings and insights.

Inclusion criteria
Studies involving undergraduate students from the medical, biomedical, dentistry, nursing and veterinary disciplines who have experienced online learning during the COVID-19 pandemic were chosen for review. The results of interest were learning outcomes (based on academic performance) and attitude of students during COVID-19 online learning (based on satisfaction, perceptions, and engagement). Both quantitative and qualitative studies were included.

Exclusion criteria
Studies that do not involve undergraduate students (such as those that are focused on postgraduate students, primary school students, and secondary school students) as well as those that investigated non-online learning were excluded. In addition, studies that include online learning but the implementation was not during the COVID-19, those that do not report students' learning outcomes and students' attitudes, as well as those not conducted in English were also excluded.

Search strategy and database used
PubMed, Scopus, and ScienceDirect were used to find articles for review. These databases were shortlisted as they subscribe to many journals that contain published articles related to the Health Sciences. All searches were done between 23 rd February 2021 to 23 rd June 2021. The Boolean operators (OR & AND) were used to combine various components when constructing the search keywords. Redundant papers were removed.
The search terms used were: PubMed (Online learning OR distance learning) AND (undergraduate student OR university student) AND (learning outcome OR skills OR competences OR satisfaction OR perspective OR reaction OR engagement) AND (COVID-19 OR coronavirus OR COVID19) Scopus (Online learning OR distance learning) AND (undergraduate student OR university student) AND (learning outcome OR skills OR competences OR satisfaction OR perspective OR reaction OR engagement) AND (COVID-19 OR coronavirus OR COVID19) ScienceDirect (Online learning) AND (university student) AND (learning outcome OR skills OR competences OR satisfaction OR perspective OR engagement) AND (COVID-19)

Screening process
The first screening was conducted after all filtered articles were exported to Mendeley. Articles' titles were screened and the abstracts of potentially relevant articles were read in full. When screening the abstract, we eliminated all articles that did not meet any of our requirements. Articles that passed the first screening were then subjected to full-text screening. They were read in full, and only those that met all our inclusion requirements were finalized and included in this systematic review. These articles were then subjected to a data extraction and analysis process after the second screening was completed.

Data analysis
All data gathered was categorized based on the results obtained from a data extraction table. New tables were created for each of the outcomes -including student perceptions, satisfaction, experience, engagement, and learning outcome. A summary of the various outcomes was conducted, which was then compared to the Kirkpatrick Model of evaluation based on four levels -Reaction, Learning, Behavior, and Results.

Quality assessment
A quality assessment was carried out using the Alberta Heritage Foundation for Medical Research's checklist (AHFMR) [18]. A two-score system was used to analyze the qualitative and quantitative aspects of the included studies. Quantitative and quantitative studies were examined based on 14 and 10 AHFMR items, respectively.

Results
A total of 1,486 studies were retrieved from three databases: PubMed, Scopus and ScienceDirect (Fig. 1). Two hundred seventeen studies were removed as duplicates by using Mendeley as the management tool and through manual screening of similar titles and abstracts. The remaining 1,269 studies were screened by title and abstract according to the eligibility criteria expounded below. Post-screening, 1,066 studies were excluded for various reasons -such as the population involved are not relevant, the intervention was not during COVID-19, the outcome presented was not relevant and clear, no full-text article, and article including another systematic review -while the remaining 203 studies were further analyzed using full-text assessments. One hundred thirty-nine studies were excluded as they did not meet the described eligibility criteria that include; the studies must only involve undergraduate students from medical and Health Science students from any country who had some experience with online learning during the COVID-19 pandemic, studies must involve online learning applications that are compared to any other teaching methods, as well as studies must include student attitudes and learning outcomes as the results to be assessed. Only 64 studies that meet the above strict criteria were chosen to be included for qualitative synthesis. Table 1 depicts the characteristics of the 64 filtered studies included in the systematic review. Among them, 56 were cross-sectional studies. Besides that, two papers were qualitative studies [19,20], two were mixed-method studies [21,22], one was a retrospective comparative cohort study [23], one a randomized controlled trial [24], one a prospective study [25] and one a case-control study [26]. Most of the papers were published in 2020 (48 of them), while the remaining 16 were published in 2021.

Characteristics of the included studies
The population involved in these studies include a mix of undergraduate students from various Health Sciences-related disciplines. Forty three studies involved the participation of undergraduate medical students, six studies involved undergraduate Health Sciences students, five studies involved undergraduate dental students, four studies involved undergraduate nursing students, two studies involved undergraduate veterinary students, two studies featuring a combination of medical and nursing students, one study featuring a combination of undergraduate medical and dentistry students, and one study involved undergraduate pharmacy students.
Most reviewed studies compared online learning applications to traditional learning approaches (62 studies). Meanwhile, there are two studies that compared online learning with blended learning approaches -a combination of online and traditional learning [27,28]. The outcomes for all studies were categorized into four main categories: learning outcomes, student perceptions, student satisfaction, and student engagement. Based on the results 40 studies reported students' perceptions, 36 reported students' satisfaction, 14 reported learning outcomes, and one reported students' engagement.

Students' perceptions on online learning
Students' perceptions on online learning were assessed using various assessment tools and was compared to their perceptions of traditional learning (Table 2). Most studies used online questionnaires as the preferred assessment tool. One study, however, leveraged online interviews. The study designs include cross-sectional, case-control, mixed, and qualitative study designs. Most studies are at Kirkpatrick level 1, while three of them are at level 2 [29][30][31] and two are at level 3 [26,32]. Table 3 displays two different aspects of perceptions that students reported on online learning -positive or negative. Generally, there were more negative perceptions on online learning reported by students than positive ones. Most studies stated that internet problems (16 In addition, seven studies reported both problems at the same time: poor internet connection as well as poor interaction and communication [19,26,31,34,45,51,61,62]. This might suggest that good internet connection may facilitate good interaction and communication. Furthermore, some studies (11) stated that when students undergo online learning, that they were concerned about not being able to practice their clinical abilities. Besides that, financial difficulties might also present a major obstacle for online learning. Technological issues such as students' and/or teachers' inexperience with internet applications, inabilities to solve technological issues, and technophobia were also mentioned.
On a similar note, students' comprehension of their subject matter may also be hampered by psychological issues such as stress and worry, lack of motivation, and difficulties in maintaining focus during classes. The disadvantages resulting from these challenges were low teaching quality, increased behavioral challenges, lots of family distractions, lack of studying spaces at home, lack of networking, difficulties in maintaining focus during long lectures, poor time-management, and increased class preparation time due to students living in different time zones than their universities and professors. On the other hand, some studies have also recorded students mentioning several advantages to online learning, which include: higher flexibility in terms of their daily schedule, less time spent on traveling to classes, lower associated costs, easier to communicate with teachers and peers, increased engagements due to higher motivation to attend classes, more time for self-study, lessons learnt online helped in clinical practices, students are able to watch and play recorded lectures at any time and place, higher interactions between students and instructors, as well as higher understanding of course content when delivered online.

Student satisfaction
There are 36 studies that examined students' satisfactions from online learning (Table 4). These studies were conducted in Asia (23 studies), Europe (10 studies), Africa (2 studies), and America (1 study). In 24 out of the 36 studies (66.7%), significant results were found to favor online learning, while the remaining 12 (33.3%) were against            it. The results were categorized into 3 levels of satisfaction which include dissatisfied, moderately satisfied, and highly satisfied. If the satisfaction of the students mentioned by the authors is under 40%, the study falls under the "dissatisfied" category. Any studies reporting scores between 40 to 70% were considered as "moderately satisfied", while those that are more than 70% were considered as "highly satisfied". A cross-continent comparison of the level of satisfaction was also conducted. From the 13 studies that       reported higher satisfaction with the use of online learning approach, six were from Asia [26,51,56,62,74,75], five were from Europe [32,41,47,66], one from America [77], and one from Africa [73]. Meanwhile, five studies from Asia [43,58,61,65,68] and one study from Africa [35] revealed that students were not satisfied with online learning. The remaining twelve studies from Asia and five studies from Europe [24,54,64,70,76] suggested that students were moderately satisfied. A comparison of Asian and non-Asian countries revealed that most studies conducted in the former reported that more than half students were moderately satisfied (52.2%) while only around one-fifth of them were dissatisfied (21.7%) with online learning. On the other hand, students in Western countries are more likely to show higher satisfaction with online classes (53.8%). However, the differences were not statistically significant (p-value = 0.214).

Learning outcomes
Fourteen studies reported learning outcomes that may be categorized into two types: 1) Based on academic performance during online learning (whether students' performance increased, decreased, or not affected); and 2) Based on skills obtained during the online learning approach (clinical or communication skills). A summary of the included studies for student learning outcomes is presented in Table 5. According to the results obtained from data analysis, seven studies examined students' academic performance, while the remaining seven examined the skills obtained during online learning (Table 6). Five studies from the former category reported increases in academic performance attributed to online learning while one study reported a decrease. On the other hand, one study reported that online learning did not affect students' academic performance. In the aspect of gained skills (the latter of the two categories), two studies found that online learning helped students in enhancing their communication skills while five others found that it helped in improving students' clinical skills.

Quality assessment
A quality assessment was carried out using the Alberta Heritage Foundation for Medical Research (AHFMR).
The results for quality assessment of the included studies were summarized in Tables 8 and 9. Most quantitative studies (62 studies) lack the following three items: 5 ("If the random allocation was possible"); 6 ("If blinding of investigators was possible"); and 7 ("If blinding of subjects was possible"). Only two studies display a percentage lower than 50% [31,44] while the remaining 61 registered a score of more than 50% each. Two studies were qualitative in nature [19,20] and the percentage scored by the two is more than 50% each.

Discussion
Time spent, content, and pedagogy during online learning can lead to noticeable differences in students' learning outcomes [33,55,82]. Nonetheless, there is still no conclusive evidence that online learning is preferable as a medium for delivering lessons [83]. Students' level of satisfaction with online learning can be influenced by their general perceptions of such delivery method [84]. Almost 50% of the studies reviewed stated that students are moderately satisfied, 37% reported that students are highly satisfied, while only 14% asserted that the students are dissatisfied. Most students mentioned flexibility (26%) as the most important factor that contributed to their satisfaction with online learning. This is possibly because they are able to log into online applications such as Zoom or Google Meet at any time of their convenience. Some students also mentioned that they had concerns about finding time to come to campus or to meet with instructors. This is especially pronounced among students living in rural areas [85]. Students also reported that online learning has helped them to be more motivated in learning. This is the case as students' were reported to feel more excited in learning to use new tools -such as new technologies that can be used to assist them during studying -effectively boosting their motivation [86].
Furthermore, according to six studies, online learning may allow for higher efficiency resulting in time savings. This is particularly true when certain lecturers swap traditional exams with reflective tasks like class conferences -where students must contribute by sharing their thoughts on what they understand about the lecturer's unique topic. This form of assessment has saved time for both students and lecturers as well as contributed to students' better comprehension [87,88]. High student-instructor interaction was also observed as online learning provides two kinds of lesson delivery tools: asynchronous and synchronous tools (such as e-mail, forums, chats, and videoconferences). These tools allow for the distribution of more content to a larger number of students and has resulted in better communication between students and instructors [89].
According to Coman et al. (2020), online learning fosters deeper understanding among students compared to traditional teaching. This improved understanding can, in turn, help students to perform better -especially in clinical practices [90]. Students also agreed that online  learning helps in saving money and/or reduces costs, especially when the students do not have to incur additional expenses on transportation to commute to their physical classes [58]. Besides that, most students stated that recorded lectures during online learning are highly useful as they may re-watch the material offered at any time of their convenience. This has allowed the students to have more time for self-study and revisions [36,62,91].
Concerning student engagement, one study found that online learning improves this aspect significantly when compared to traditional learning methods [23]. This study utilized retrospective cohort studies to examine students' questioning behavior in face-to-face versus online classes. According to the findings, students are more likely to ask questions during online learning than during face-to-face learning. The queries asked by students are also more complicated. The researchers concluded that this was the case as students do not need to raise their hands or speak directly to instructors to ask a question in an online learning setting. Instead, they can type their questions in the chat box and submit them anonymously. A timid student who constantly hesitates to ask questions during physical in-person class can benefit from these tools as they provide the much needed anonymity. The chat or question box will remain visible until the end of the session, which allow other students to respond to the question or participate in the discussion.
On a different note, students who were not satisfied with online learning complained that internet problems and sub-par communications between students and instructors as among the factors that contributed to their dissatisfaction. High bandwidth and a robust internet connection are required for a seamless experience during online classes. However, not all students can afford them. This has resulted in many students experiencing problems with their internet connection despite having cellular data or Wi-Fi connections at home. Subpar communications between students and instructors may happen due to the lack of effective interactions that occur when instructors are unable to monitor their students as effectively as they could in a physical setting. In addition, instructors would not be able to meet and discuss with their students as frequently as they would like -to some student's dismay [92]. Because students and teachers would not physically observe each other's body language in an online setting, maintaining an effective communication has become more challenging and requires more effort than face-to-face sessions. During in-person lectures, lecturers can easily use body language and facial expressions to help students understand the content more effectively. Nevertheless, these elements are usually not present in an online setting (or not as pronounced), making communications more difficult and resulting in sub-par interactions between students and instructors [93].
According to Chan et al. (2020), experience-based learning is very important for students to gain new experiences as they participate in various activities involving patients and clinical teachers [94]. However, because of the pandemic and the associated travel restrictions, most activities can only be completed online via Zoom or Google Meet. This has directly impacted students'         = Result support the conclusions performances in their clinical practices. Some students also mentioned that they are worried that missing physical clinical training during their degrees might lead them to lose their job opportunities in the future [95]. This challenge is further exacerbated as some students also lack familiarity with technology and often encounter technological issues such as incompatibility of online learning software with their computer's operating system and the browsers they use. In addition, some cellphones can only support a limited number of applications [92]. According to Sitzmann et al. (2010), students' learning outcomes might be significantly impacted by technical difficulties leading to an increase in students' displeasure [96].
Besides that, online learning might create anxiety and depression among students. This is especially pertinent during the Covid-19 quarantine period as university students are more likely to get stress disorders and depression due to prolonged social isolation, which can exacerbate procrastination and a sense of worthlessness [97]. Moreover, technophobia -defined as a fear of technology that stems from unfavorable encounters with it -may foster students' hesitant attitude towards online learning [98].
As suggested Rasmitadila et al. (2020), students tend to lose attention during online learning sessions due to a variety of factors including family distractions and the lack of a conducive setting for learning [99]. Family distractions -especially for students with large immediate families and who do not have a conducive setting for learning (where students have no choice but to study in the living room while their family members are around) -can negatively impact students' learning experience significantly. Furthermore, some students stated that they were having financial difficulties that hinder them from affording a data plan and strong Wi-Fi for online learning. In addition to that, some students asserted that time management is extremely difficult during the pandemic as they are not constantly supervised by their lecturers, effectively leading to their sub-par performances [100].
According to Gustiani (2020), online learning caused\s some students to lose motivation in their studies. This might occur due to a couple of factors including unfavorable learning environments (for example, there are parents that ask their children to do household chores during online lessons) [86]. Online learning exams have also been shown to result in behavioral changes in students -such as changing dietary behaviors, inconsistent sleeping patterns, and deterioration of physical exercise [43]. Besides that, students also complained about the length of online tests as some of them did not have enough time to answer all questions given. This could be attributed to technical issues that occurred during the online test (including lagging and/or slow laptops). Because of these issues, the students believed that more time was needed to prepare during online tests in comparison to their traditional counterparts [101]. On a similar note, in a study where the delivery of educational information via live streaming sessions by instructors required good internet bandwidth to get the best streaming quality, low teaching standards have been reported by students. [33]. According to Co et al., (2021), students reported that they were unable to collaborate with a subject matter expert throughout the online learning process due to the lack of networking [26]. Some international students also experienced difficulties due to the difference in time zones between their home countries and their universities [53].
Most studies conducted are in the field of medical education. The evaluation of the effectiveness of online learning was done based on students' academic performance as well as the skills they obtained through the lessons. Five studies (72%) reported an increase in academic performance when compared to the traditional approach, one study (14%) reported a decrease in academic performance, while one study (14%) concluded that students are not affected by the different delivery methods. These results demonstrate that student performance can improve with the use of online learning during a pandemic. According to Gonzalez et al. (2020), during the pandemic, more students started to pass their courses and more students finished their assignments than in prior years [102]. Because of this, they suggest that the rise in students' academic performance is related to the Table 9 Summary of quality assessment for qualitative studies Note: Yes = 2, Partial = 1, No = 0 Q1 = Question or objective sufficiently described Q2 = Design evident and appropriate to answer study question Q3 = Context of the study clear Q4 = Connection to a theoretical framework/wider body of knowledge? Q5 = Sampling strategies described, relevant and justified? Q6 = Data collection method clearly describe and systematic? Q7 = Data analysis method clearly describe and systematic? Q8 = Use verification procedure to establish credibility? Q9 = Conclusions supported by results Q10 = Relativity of the account? greater constancy in studying as the results of online learning arrangements. Finally, the improvement in students' performance may also be attributed to the lack of distractions. Some students -particularly the low-performing ones -may be less distracted by their peers if they learn at home. This has allowed them to focus more on their studies and, as a result, improve their academic performance [103][104][105].

Reference
Most studies agreed that online learning could help students improve their skills such as communication and clinical skills. Two studies stated that online learning improves the former, while five studies suggested that it improves the latter. According to results obtained from Gormley et al. (2009), online learning had a positive impact on students' clinical skills [106]. Most of the students surveyed in their study agreed that the lessons on clinical capabilities that they get through online learning were on par with those obtained through traditional physical setting. Furthermore, the researchers claimed that students who exhibit characteristics related to deeper learning in clinical skills would perform better when learning online. In addition, students were also quite comfortable with the usage of internet video and photographs during clinical procedures. With regards to improvements in communication skills, Rodrigues and Vethamani (2015) found that online learning approaches may assist students in acquiring these skills [107]. Online learning can motivate students to practice their oral communication skills in a one-on-one learning environment that is critical for them to develop their self-confidence.
Based on the screened articles, the two countries that exhibit the highest number of studies not in favor of online learning applications are India [45,59,68] and Jordan [33,43,58,108]. The biggest challenge to implement online learning as observed in India is the lack of accessibility. The overall number of internet users in India is estimated to be around 564.5 million in 2020, although the entire population in the same year was around 1.38 billion. This implies that more than half of the population lacked access to the internet during the pandemic [109]. Most Indian families face financial difficulties that hinder their children from having their own equipment such as laptops, PCs, and cell phones for online learning use. Some families with multiple children also reported having difficulties enrolling themselves in online programs and lessons, as the entire family depends on a single gadget at home that must be shared with everyone [110].
Along a similar line, the lack of electricity has also been identified as one of the hurdles of online learning, particularly for students who live in remote areas. The lack of electricity contributed to minimal internet penetration resulting in poor internet speeds [111]. According to Aljaraideh and Bataineh (2019), the lack of adequate online learning infrastructure is the most frequently reported difficulty in online learning by students in Jordan [112]. Furthermore, their study stated that the impact of the existing weak infrastructure could be compounded by the lack of proper assistance from the government and higher education's top administration.

Kirkpatrick evaluation
Kirkpatrick Evaluation was utilized to acquire a thorough grasp of how online classes influence learning and whether there is a major difference in how students learn. 80% of the studies access the effectiveness of online learning based on Level 1 (Reaction), 8% based on level 2 (Learning), 12% based on Level 3 (Behavior), while no studies were accessed based on Level 4 (Results).
According to the Kirkpatrick evaluation, most studies reviewed were evaluated at Level 1 (Reaction), which is based on students' "reactions" to online learning. Only a few studies were evaluated at Level 2 (Learning) and Level 3 (Behavior), while none were evaluated at Level 4 (Result). Future research should concentrate on analyzing the effectiveness of online learning at higher levels of the Kirkpatrick model -such as Level 3 (Behavior) and Level 4 (Result) -as studies performed at these levels can yield more consistent results. Furthermore, future studies should entail the usage of Randomized Clinical Trials (RCT) and qualitative research methods. This is because these study designs are more dependable (in comparison to a simple cross-sectional study design), allowing for more accurate conclusions to be drawn.

Limitation of this study
The main limitation of this study is that it involves the review of many cross-sectional studies. Only three studies were non-cross-sectional by design -one utilized Randomized Controlled Trials (RCTs) and two others were qualitative in nature. According to Levin (2006), cross-sectional studies are not the most reliable for making causal inferences, while prejudice (Neyman bias) is more likely to emerge during the research process. RCTs have a significant benefit over other study designs that use a randomization technique [113]. Allocation bias and confounding or unknown variables can be reduced by randomly assigning individuals to the test and control groups. Compared to other study designs, RCTs can also be utilized to make causal inferences and provide the strongest empirical evidence [114]. Our study may have reached some inaccurate conclusions due to the small number of RCTs and qualitative studies screened. To summarize, in the field of education, it is not enough to just question "what works", It is also necessary to ask "what works for whom, in what circumstances, and in connection to what" in order to reach to a sound and reliable conclusion [12].

Conclusion
School cancellations caused by COVID-19 have caused enormous disturbances in the education sectors across various countries, significantly altering how students are educated. The efficiency of online learning was assessed in this systematic review based on a variety of parameters based on the Kirkpatrick model of evaluation. The parameters include students' reaction and attitudes (perceptions/ satisfactions/ engagements), as well as students' learning outcome. According to most studies, students' overall satisfaction with online learning applications is higher vis-à-vis traditional teaching techniques. Students believed that online learning provides various advantages including greater flexibility, boosts students' motivation, as well as offers various time and cost savings. However, most studies found that internet connectivity issues and low interaction between instructors and learners are among the most significant drawbacks of this approach. Studies that investigated learning outcomes as a major performance indicator for online learning, on the other hand, found that this learning method helps students improve their academic performance as well as clinical and communication skills.