Fix threshold issue

youden_index.py

@@ -109,7 +109,7 @@ class YoudenIndex(evaluate.Metric):
         # 2. Determine the optimal threshold based on the Youden index
         fpr, tpr, thresholds = roc_curve(references, prediction_scores)
         idx = np.argmax(tpr - fpr)
-        optimal_threshold = thresholds[::-1][idx + 1]
+        optimal_threshold = thresholds[idx-1]
         # 3. Calculate PPV (precision) and NPV based on the optimal threshold
         optimal_predictions = np.where(prediction_scores > optimal_threshold, 1, 0)
         ppv = precision_score(references, optimal_predictions)
@@ -121,5 +121,4 @@ class YoudenIndex(evaluate.Metric):
             "roc_auc": roc_auc,
             "ppv": ppv,
             "npv": npv,
-            "idx": idx,
         }