262 Chapter 10 the surgery and the different perioperative events. The selection of one of the labels automatically marked the time code corresponding to the moment the label was pressed. This made it possible to measure the duration of the phases and perioperative events. The labels used for this analysis are given in Fig. 3. The steps correspond to the different steps in the PROTEST assessment method.22 The second category encompassed perioperative events that could be related to postoperative outcomes. These events were defined in the PROTEST assessment method.22 Data analysis Data analysis was performed using SPSS statistics v24 (IBM, NY). Frequency statistics were calculated for patient demographic data and surgeon scores. Correlation between observed scores on the one hand and postoperative functional outcome on the other hand were calculated using a Spearman Rho test. Odd ratios (OR) and 95% confidence intervals (CIs) were calculated. The Wilcoxon signed-rank test was used to compare differences in results between the matched patient groups. McNemar’s test was used in order to compare differences in results between the matched patient groups in case of dichotomous variables. The predictions by the experts were correlated with the postoperative status of the patients using a crosstab. To determine any significant correlations between variables, Pearson’s chi square or Fisher’s exact tests were used. Interobserver agreement was calculated using Cohen’s kappa, which was interpreted using the guidelines from Landis and Koch30,31. Statistical significance was set at p < 0.05 based on a two-tailed comparison. Due to the retrospective nature of the study, participants were not subjected to any study treatments or actions. Surgical videos and medical information used were registered as the standard of care in the medical files of the patients. Therefore, the Medical Research Involving Human Subjects Act does not apply, and no informed consent was obtained. However, during the screening of patients, the medical records were carefully checked for objection to medical research. This study was granted approval from the institutional medical committee. Figure 3 overview of the labels used in the PROTEST analysis using software Digital Video Coach
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