Figure 3b. ROC plots (ROC curves generated by locally-weighted scatterplot smoothing) for detecting and grading mitral valve insufficiency. (a) Plot of grade 0 versus grades I–IV. The optimal threshold for detecting echocardiographic grades I–IV is regurgitation fraction of 6% (sensitivity, 89%; specificity, 81%; PPV, 92%; NPV, 74%). (b) Plot of grades 0–I versus grades II–IV. The optimal threshold for detecting echocardiographic grades II–IV is regurgitation fraction of 20% (sensitivity, 88%; specificity, 87%; PPV, 82%; NPV, 91%). (c) Plot of grades 0–II versus grades III–IV. The optimal threshold for detecting echocardiographic grade III–IV is regurgitation fraction of 30% (sensitivity, 86%; specificity, 92%; PPV, 76%; NPV, 96%). (d) Plot of grades 0–III versus grade IV. The optimal threshold for detecting echocardiographic grade IV is regurgitation fraction of 44% (sensitivity, 93%; specificity, 91%; PPV, 41%; NPV, 99%).