Student engagement in a flipped undergraduate medical classroom to measure optimal video-based lecture length.

To determine the optimal length of video-based lectures for undergraduate medical students in a flipped classroom environment and evaluate the effect of their length on student engagement outcomes. Using an observational cohort study, 152 students (male = 38 and female = 114) viewed 173 videos focused on teaching Neurosurgery over three consecutive academic years. Each course consisted of 11 topics divided into a variable number of clips. Materials, methodology, and instructors remained constant throughout the study period. All students enrolled in the subject were invited to register on the online platform hosting the videos voluntarily. Data on course variables, video-based lecture characteristics, and six student engagement outcomes were analyzed. Videos under 5 minutes in length were associated with higher audience retention and higher response rates to embedded questions in the univariable analysis (p = 0.039 and p = 0.045, respectively). The viewing index, which can be equated to cumulative views, was also higher for videos under 5 minutes after multiple regression analysis (p = 0.049). Videos released earlier in the course and those related to a seminar session (with mandatory homework and class attendance) had significantly higher percentages of video viewing, viewing index, and response rate to embedded questions but lower non-access rates. In addition, earlier videos retained more audience (p = 0.036). This study provides new insights by analyzing the interaction between video duration and various engagement metrics, highlighting the importance of instructional design in flipped learning environments. The findings support the recommendation that video length should be under 5 minutes. However, this is not the only determining factor; the timing of the video release and the seminar structure can also play a crucial role. Other unmeasured classroom dynamics need to be considered for further studies that should explore these interactions in more depth.