Fig. 3

Calibration of the ROX index. We categorized patients into three risk groups based on their ROX index: high (ROX index < 3.85), intermediate (3.85 ≤ ROX index ≤ 4.88), and low (ROX index > 4.88). Calibration of the ROX index is illustrated; at 2 h, approximately 40%, 57%, and 53% of patients in the low-, intermediate-, and high-risk groups, respectively, experienced treatment failure, indicating that the ROX index was not well calibrated. Treatment failure was defined as either intubation or death within 7 days