diff --git a/fast_carpenter/summary/binned_dataframe.py b/fast_carpenter/summary/binned_dataframe.py
index cd1839f..a3df678 100644
--- a/fast_carpenter/summary/binned_dataframe.py
+++ b/fast_carpenter/summary/binned_dataframe.py
@@ -150,6 +150,11 @@ def __init__(self, name, out_dir, binning, weights=None, dataset_col=False):
         excluded from the stored dataframe.  Leaving this ``False`` can save
         some disk-space and improve processing time, particularly if the bins are
         only very sparsely filled.
+      observed (bool): If ``False`` bins in the dataframe will only be filled
+        if their are datapoints contained within them.  Otherwise, depending on
+        the binning specification for each dimension, all bins for that
+        dimension will be present.  Use `pad_missing: true` to force all bins
+        to be present.
 
     Other Parameters:
       name (str):  The name of this stage (handled automatically by fast-flow)
@@ -161,7 +166,8 @@ def __init__(self, name, out_dir, binning, weights=None, dataset_col=False):
 
     """
 
-    def __init__(self, name, out_dir, binning, weights=None, dataset_col=True, pad_missing=False, file_format=None, observed=False):
+    def __init__(self, name, out_dir, binning, weights=None, dataset_col=True,
+                 pad_missing=False, file_format=None, observed=False):
         self.name = name
         self.out_dir = out_dir
         ins, outs, binnings = cfg.create_binning_list(self.name, binning)
diff --git a/tests/summary/test_binned_dataframe.py b/tests/summary/test_binned_dataframe.py
index 87e5df9..b49a821 100644
--- a/tests/summary/test_binned_dataframe.py
+++ b/tests/summary/test_binned_dataframe.py
@@ -115,7 +115,7 @@ def test_BinnedDataframe_run_twice(binned_df_1, tmpdir, infile):
     assert totals["EventWeight:sumw"] == pytest.approx(231.91339 * 2)
 
 
-@pytest.fixture #(scope="function")
+@pytest.fixture
 def run_twice_data_mc(config_1, infile, observed):
     chunk_mc = FakeBEEvent(infile, "mc")
     chunk_data = FakeBEEvent(infile, "data")