Background: In-hospital mortality in trauma patients decreased recently owing to improved trauma injury prevention systems. However, no study which evaluated the validity of Trauma and Injury Severity Score (TRISS) in pediatrics by detailed classification of patients' age and injury severity in Japan. This retrospective nationwide study evaluated the validity of TRISS in predicting survival in Japanese pediatric patients with blunt trauma by age and injury severity.Methods: Data were obtained

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... om the Japan Trauma Data Bank during 2009−2018.Results: In all age categories, the area under the curve (AUC) for TRISS demonstrated high performance (0.935, 0.981, 0.979, and 0.977). The Accuracy of TRISS was 99.9%, 98.2%, 92.1%, 76.7%, 55.3%, and 72.1% in survival probability (Ps) interval groups (0.96−1.00), (0.91−0.95), (0.76.−0.90), (0.51−0.75), (0.26−0.50), and (0.00−0.25), respectively. The AUC for TRISS demonstrated moderate performance in the Ps interval group (0.96−1.00) and low performance in other Ps interval groups.Conclusions: The TRISS methodology appears to predict survival accurately in Japanese pediatric patients with blunt trauma; however, there were several problems in adopting the TRISS methodology for younger blunt trauma patients with higher injury severity. In the future, we should consider to conducting a simple, high-quality prediction model that is more suitable for pediatric trauma patients than the current TRISS model.