## 5 Results
### Medical Interpretation of Explainability Results  
The application of XAI techniques to the 3P-U model revealed key features that significantly influenced admission predictions in the ED, including heart rate, patient age, arrival with multiple severe injuries, and a FRENCH triage grade of 2. These XAI results are in line with well-established medical knowledge as follows: Firstly, the higher likelihood of admission for older patients can be attributed to their increased frailty, and short- or mid-term discharge tends to be more complex [70]. Secondly, patients with severe injuries often undergo at least 24 h of monitoring, even when the initial additional examinations (lab tests, imaging, etc.) give normal results. It has been reported that the first whole-body CT scan misses severe injuries in 10% of cases, with clinical relevance in 6.7% and no clinical relevance in 3.7% [71]. Thirdly, an abnormal heart rate is a common indicator of a severe medical condition, including cardiovascular disease [72], sepsis [73], and post-surgical bleeding [74].  
Conversely, features like 'Waiting standing or in a wheelchair' and 'Arrival in the ED by one's own means' accounted for a substantial proportion of discharge predictions. One can reasonably hypothesize that a patient who has waited for test results while standing or sitting is more likely to be discharged from the ED. In such cases, the condition may  
Figure 5: The PDP for heart rate. The solid dark line represents the mean predicted outcome across age, with individual points indicating specific heart rates at which predictions were calculated. The shaded area around the curve represents the 95% confidence interval of the predictions. The horizontal dashed red line marks the baseline reference at zero, facilitating visual interpretation of deviations from baseline.  
not have necessitated lying down on a stretcher--making outpatient care more probable, irrespective of the final diagnosis.  
The PDP explainability analysis identified other features of clear relevance for predicting hospital admission, including high capillary blood levels of ketones, glucose, and alcohol, a FRENCH triage grade of 2, and jaundice. These results have compelling clinical explanations. Firstly, elevated capillary blood ketone and glucose levels indicate a high likelihood of a decompensated diabetic disorder, possibly accompanied by acidoketosis [75]. This type of condition often necessitates hospital admission for appropriate management and care. Secondly, the FRENCH triage grade 3 corresponds to relatively urgent cases requiring treatment following a nurse evaluation, while grades 4 or 5 denote less urgent situations. As urgency increases, so does the likelihood of admission [55]; this explains the impact of this triage grade on the prediction of admission. Thirdly, jaundice indicates a hepatic or biliary disorder requiring hospital treatment. Given its medical significance, jaundice influences the decision to admit patients exhibiting this sign.  
The results given by the SHAP and PDP XAI techniques reinforce the importance of these features and validate their use by emergency physicians to determine whether a patient should be admitted or discharged. There was no discordance between the two experts; the rate agreement was 100%. By shedding light on the clinical significance of these predictors, the XAI analysis bolsters the model's credibility and its alignment with medical decision-making practices in the ED.