## 4 Discussion  
Nowadays, teaching is shifting towards a non-classroom model due to technological advances and, unfortunately, the situation imposed due to COVID-19. Thus, studying the degree of confidence of an online teaching model and comparing it with a traditional teaching model is especially relevant. The most important results from this study were those from the propensity analysis, which gave higher probability of obtaining better results in terms of theoretical as well as practical exams for both online groups compared to the traditional teaching groups. These results could be due to the fact that online groups had the possibility to watch the videos more than once compared to the onsite groups who attended the theoretical classes only at the scheduled time. To the best of our knowledge, this is the first time that results of online versus onsite education, both theoretical and practical, have been compared, indicating comparable results. Other studies [29; 31] comparing traditional teaching with online teaching showed good results for both groups but without differences between groups. [PERSON] et al. [27] used a mobile app for ultrasound exploration versus traditional exploration, and found no significant difference between groups in the acquisition of theoretical and practical knowledge. Furthermore, a differentiating element between studies was that while [PERSON] et al. only evaluated the shoulder, in our study, we evaluated the main basic anatomical regions used in physical therapy. [PERSON] et al. [32] also found an improvement for both groups receiving face-to-face and DVD instruction, though no differences between groups. This discrepancy between our study and theirs when comparing groups could be explained by the possibility our online group had to practice with the ultrasound devices prior to exams. In other health sciences specialties, digital media have been used for training, finding increases in sensitivity of 86.6% and specificity of 85.6% for the detection of pneumothorax [33], as well as in transesophageal echocardiography [31], where an improvement of 60% was found; however, they used attendants who had previous or basic ultrasound education. The results obtained in our study for the scores of the theoretical exam did not indicated very large differences between the Online 1 and Onsite 1 groups (0.6708, SE = 0.2680) but significant differences were found between the Online 2 and Onsite 2 groups (1.1832, SE = 0.5425), probably due to cumulative education time in favor of the online group. These results are in discordance with previous studies [29; 31]; however, [PERSON] et al. [31] and [PERSON] et al. [33] concluded that online teaching could be beneficial when associated with traditional training. For the practical exam, our results showed significant differences between the Online 2 and Onsite 1 groups (1.5026, SE = 0.5822) in the Solid_structure_surface_distance variable. The other measurements did not show significant differences between groups. This could be interpreted as indicating that a minimum level of ultrasound education must be offered to trust the precision of practical results that attendants can achieve. The results of ICC obtained in the Online 2 group were excellent (ICC = 0.94) and the differences were considered high compared with the other groups. This could be due to bad visibility when performing the in-depth measurement or some bias in the collection of the results since the attendants (online and onsite) sent the scores through a Google form. Which could be avoided by a test-retest prior the sampling. It is possible that some samples obtained used different references in the phantom, despite the indications received. Therefore, it would be necessary to improve the agreement at the measurement points considering the differences in the ICCs (Table 3).