Multi-environment evaluation and decision-level analysis of clinical prediction models under dataset shift

Clinical machine-learning models are often evaluated within a single dataset, although deployment occurs across heterogeneous institutions and measurement processes. We evaluated Logistic Regression, Random Forest, and Gradient Boosting for ICU hospital-mortality prediction across MIMIC-III Demo and eICU using a 24-h landmark design, explicit feature mappings, and predictors retained only when sufficiently observed in both domains. A decision-level diagnostic analysis examined how predicted-probability distributions interact with a fixed 0.5 threshold. The primary cohort contained 110 MIMIC and 1,324 eICU ICU episodes. In eICU-to-MIMIC transfer, AUC-ROC was 0.598 for Logistic Regression, 0.642 for Random Forest, and 0.613 for Gradient Boosting. Random Forest generated no positive predictions, a threshold failure already visible during internal eICU validation. Logistic Regression retained partial sensitivity with substantial false-positive burden, whereas Gradient Boosting detected only two deaths. These findings show that clinical model evaluation should examine calibration, threshold behavior, feature harmonization, and source-to-target operating-point stability, not only aggregate discrimination.