diff --git a/causalpy/pymc_experiments.py b/causalpy/pymc_experiments.py
index 502c0d41..c07bb1a6 100644
--- a/causalpy/pymc_experiments.py
+++ b/causalpy/pymc_experiments.py
@@ -26,7 +26,7 @@
 from causalpy.custom_exceptions import BadIndexException  # NOQA
 from causalpy.custom_exceptions import DataException, FormulaException
 from causalpy.plot_utils import plot_xY
-from causalpy.utils import _is_variable_dummy_coded, _series_has_2_levels
+from causalpy.utils import _is_variable_dummy_coded
 
 LEGEND_FONT_SIZE = 12
 az.style.use("arviz-darkgrid")
@@ -978,7 +978,8 @@ class PrePostNEGD(ExperimentalDesign):
     :param formula:
         A statistical model formula
     :param group_variable_name:
-        Name of the column in data for the group variable
+        Name of the column in data for the group variable, should be either
+        binary or boolean
     :param pretreatment_variable_name:
         Name of the column in data for the pretreatment variable
     :param model:
@@ -1058,17 +1059,19 @@ def __init__(
                 self.group_variable_name: np.zeros(self.pred_xi.shape),
             }
         )
-        (new_x,) = build_design_matrices([self._x_design_info], x_pred_untreated)
-        self.pred_untreated = self.model.predict(X=np.asarray(new_x))
+        (new_x_untreated,) = build_design_matrices(
+            [self._x_design_info], x_pred_untreated
+        )
+        self.pred_untreated = self.model.predict(X=np.asarray(new_x_untreated))
         # treated
-        x_pred_untreated = pd.DataFrame(
+        x_pred_treated = pd.DataFrame(
             {
                 self.pretreatment_variable_name: self.pred_xi,
                 self.group_variable_name: np.ones(self.pred_xi.shape),
             }
         )
-        (new_x,) = build_design_matrices([self._x_design_info], x_pred_untreated)
-        self.pred_treated = self.model.predict(X=np.asarray(new_x))
+        (new_x_treated,) = build_design_matrices([self._x_design_info], x_pred_treated)
+        self.pred_treated = self.model.predict(X=np.asarray(new_x_treated))
 
         # Evaluate causal impact as equal to the trestment effect
         self.causal_impact = self.idata.posterior["beta"].sel(
@@ -1079,7 +1082,7 @@ def __init__(
 
     def _input_validation(self) -> None:
         """Validate the input data and model formula for correctness"""
-        if not _series_has_2_levels(self.data[self.group_variable_name]):
+        if not _is_variable_dummy_coded(self.data[self.group_variable_name]):
             raise DataException(
                 f"""
                 There must be 2 levels of the grouping variable
@@ -1165,7 +1168,7 @@ def _get_treatment_effect_coeff(self) -> str:
         then we want `C(group)[T.1]`.
         """
         for label in self.labels:
-            if ("group" in label) & (":" not in label):
+            if (self.group_variable_name in label) & (":" not in label):
                 return label
 
         raise NameError("Unable to find coefficient name for the treatment effect")