fixed stderr for metrics like brier_score

lm_eval/evaluator.py

@@ -487,23 +487,34 @@ def evaluate(
                         # For unweighted averaging, use:
                         #     current_size = 1
 
+                        # TODO: Tasks like brier score for individual 
+                        # tasks have no stderr since the score is 
+                        # itself an aggregation. But it's possible to 
+                        # calculate the stderr over groups
+
                         all_stderr = []
                         for metric in [
                             key for key in metrics.keys() if "_stderr" not in key
                         ]:
                             stderr = "_stderr,".join(metric.split(","))
                             stderr_score = results[task][stderr]
+                            if stderr_score == "N/A":
+                                var_score = "N/A"
+                            else:
                                 var_score = stderr_score**2
-                            metric_score = results[task][metric]
-
                                 all_stderr.append(stderr)
 
+                            metric_score = results[task][metric]
+
                             if metric in results[group]:
                                 results[group][metric] = (
                                     results[group][metric] * total_size
                                     + metric_score * current_size
                                 ) / (total_size + current_size)
                                 # $$s_z^2 = \frac{(n-1) s_x^2 + (m-1) s_y^2}{n+m-1} + \frac{nm(\bar x - \bar y)^2}{(n+m)(n+m-1)}.$$
+                                if var_score == "N/A":
+                                    results[group][stderr] = "N/A"
+                                else:
                                     results[group][stderr] = (
                                         (total_size - 1) * results[group][stderr]
                                         + (current_size - 1) * var_score