updated group metrics calculation

Author: AndreFCruz

folktexts/evaluation.py

@@ -81,7 +81,8 @@ def evaluate_binary_predictions_fairness(
     y_true: np.ndarray,
     y_pred: np.ndarray,
     sensitive_attribute: np.ndarray,
-    return_groupwise_metrics: Optional[bool] = False,
+    return_groupwise_metrics: bool = False,
+    min_group_size: float = 0.04,
 ) -> dict:
     """Evaluates fairness of the given predictions.
 
@@ -96,9 +97,14 @@ def evaluate_binary_predictions_fairness(
         The discretized predictions.
     sensitive_attribute : np.ndarray
         The sensitive attribute (protected group membership).
-    return_groupwise_metrics : Optional[bool], optional
+    return_groupwise_metrics : bool, optional
         Whether to return group-wise performance metrics (bool: True) or only
         the ratios between these metrics (bool: False), by default False.
+    min_group_size : float, optional
+        The minimum fraction of samples (as a fraction of the total number of
+        samples) that a group must have to be considered for fairness
+        evaluation, by default 0.04. This is meant to avoid evaluating metrics
+        on very small groups which leads to noisy and inconsistent results.
 
     Returns
     -------
@@ -124,6 +130,10 @@ def group_metric_name(metric_name, group_name):
         # Indices of samples that belong to the current group
         group_indices = np.argwhere(sensitive_attribute == s_value).flatten()
 
+        if len(group_indices) < min_group_size * len(y_true):
+            logging.warning(f"Skipping group {s_value} with {len(group_indices)} samples")
+            continue
+
         # Filter labels and predictions for samples of the current group
         group_labels = y_true[group_indices]
         group_preds = y_pred[group_indices]
@@ -144,8 +154,9 @@ def group_metric_name(metric_name, group_name):
     # Compute ratios and absolute diffs
     for metric_name in unique_metrics:
         curr_metric_results = [
-            groupwise_metrics[group_metric_name(metric_name, group_name)]
+            groupwise_metrics[curr_group_metric_name]
             for group_name in unique_groups
+            if (curr_group_metric_name := group_metric_name(metric_name, group_name)) in groupwise_metrics
         ]
 
         # Metrics' ratio