The ‘reported clinical status’ was compared with a ‘corrected clinical status’ following reclassification based on the standard definition calculated from raw data. Observed-to-predicted risk ratios (OPRs) of 30-day mortality were calculated for the model using reported status and corrected status and compared. A Bland-Altman plot was generated to examine the level of agreement between the two OPRs.
Of 18496 cases reported as urgent, 49.9% were operated after 72 hours, leading to misclassification of 14.6% in the registry. Misclassified patients had significantly higher mortality (3.5%) than true urgent patients (2.9%). Underweight (OR:1.6,CI:1.2-2.1), dialysis (OR:1.4,CI:1.1-1.7), endocarditis (OR:2.1,CI:1.7-2.5), shock (OR:1.6,CI:1.3-2.0) and poor ejection fraction (OR:1.2,CI:1.1-1.4) were significant predictors of misclassification. Bland- Altman plot demonstrates significant disagreement between two risk estimates (P<0.001). Misclassification results in overestimation of risk by 9.1%. Observed-to-predicted risk increased with corrected definition (0.8975 vs 0.9875), suggesting poorer calibration with reported status.
In the ANZSCTS database, misclassification prevalence is 14.6%. Misclassification compromises the discrimination capacity and calibration of the model and results in overestimation of mortality risk.