update statistics for utest

mlair/helpers/statistics.py

@@ -275,7 +275,8 @@ def represent_p_values_as_asteriks(p_values: pd.Series, threshold_representation
             f"`threshold_representation' keys mus be in strictly "
             f"decreasing order but is: {threshold_representation.keys()}")
 
-    asteriks = pd.Series().reindex_like(p_values)
+    # asteriks = pd.Series().reindex_like(p_values)
+    asteriks = pd.DataFrame().reindex_like(p_values)
     for k, v in threshold_representation.items():
         asteriks[p_values < k] = v
     return asteriks