diff --git a/python/uatk_spc/reader.py b/python/uatk_spc/reader.py
index 543f430..ee8ee61 100644
--- a/python/uatk_spc/reader.py
+++ b/python/uatk_spc/reader.py
@@ -11,6 +11,17 @@
 # - Add graph data structure reading for flows (e.g. into networkx)
 
 
+# Type alias for a dataframe
+DataFrame = pd.DataFrame | pl.DataFrame
+
+
+def backend_error(backend: str) -> ValueError:
+    ValueError(
+        f"Backend: {backend} is not implemented. Use 'polars' or 'pandas' instead."
+    )
+
+
+# TODO: refactor with single class handling either proto or parquet
 class SPCReaderProto:
     """
     A class for reading from protobuf into ready to use data structures.
@@ -27,9 +38,9 @@ class SPCReaderProto:
     """
 
     pop: synthpop_pb2.Population()
-    people: pl.DataFrame
-    households: pl.DataFrame
-    time_use_diaries: pl.DataFrame
+    people: DataFrame
+    households: DataFrame
+    time_use_diaries: DataFrame
     venues_per_activity: Dict[str, Any]
     info_per_msoa: Dict[str, Any]
 
@@ -48,10 +59,8 @@ def __init__(self, path: str, region: str, backend="polars"):
                 pop_as_dict["timeUseDiaries"]
             )
         else:
-            raise ValueError(
-                f"Backend: {backend} is not implemented. Use 'polars' or 'pandas' "
-                f"instead."
-            )
+            raise backend_error(backend)
+
         self.venues_per_activity = pop_as_dict["venuesPerActivity"]
         self.info_per_msoa = pop_as_dict["infoPerMsoa"]
 
@@ -76,13 +85,16 @@ class SPCReaderParquet:
             format.
         venues_per_activity (Dict[str, Any]): Venues per activity as a Python dict.
         info_per_msoa (Dict[str, Any]): Info per MSOA as a Python dict.
+        backend (str): DataFrame backend being used, must be either 'polars' or
+            'pandas'
     """
 
-    people: pl.DataFrame
-    households: pl.DataFrame
-    time_use_diaries: pl.DataFrame
-    venues_per_activity: pl.DataFrame
+    people: DataFrame
+    households: DataFrame
+    time_use_diaries: DataFrame
+    venues_per_activity: DataFrame
     info_per_msoa: dict
+    backend: str
 
     def __init__(self, path: str, region: str, backend="polars"):
         path_ = os.path.join(path, region)
@@ -91,27 +103,23 @@ def __init__(self, path: str, region: str, backend="polars"):
             self.people = pl.read_parquet(path_ + "_people.pq")
             self.time_use_diaries = pl.read_parquet(path_ + "_time_use_diaries.pq")
             self.venues_per_activity = pl.read_parquet(path_ + "_venues.pq")
+            self.backend = "polars"
         elif backend == "pandas":
             self.households = pd.read_parquet(path_ + "_households.pq")
             self.people = pd.read_parquet(path_ + "_people.pq")
             self.time_use_diaries = pd.read_parquet(path_ + "_time_use_diaries.pq")
             self.venues_per_activity = pd.read_parquet(path_ + "_venues.pq")
+            self.backend = "pandas"
         else:
-            raise ValueError(
-                f"Backend: {backend} is not implemented. Use 'polars' or 'pandas' "
-                f"instead."
-            )
+            raise backend_error(backend)
+
         with open(path_ + "_info_per_msoa.json", "rb") as f:
             self.info_per_msoa = json.loads(f.read())
 
-    def __summary(
-        self, df: pl.DataFrame
-    ) -> Dict[str, List[pl.datatypes.classes.DataTypeClass]]:
+    def __summary(self, df: DataFrame) -> Dict[str, List[Any]]:
         return dict(zip(df.columns, df.dtypes))
 
-    def summary(
-        self, field: str
-    ) -> Dict[str, List[pl.datatypes.classes.DataTypeClass]] | None:
+    def summary(self, field: str) -> Dict[str, List[Any]] | None:
         """Provides a summary of the given SPC field.
 
         Args:
@@ -146,19 +154,29 @@ def summary(
                 )
             )
 
-    def merge(self, left: str, right: str, **kwargs) -> pl.DataFrame:
+    def merge(self, left: str, right: str, **kwargs) -> DataFrame:
         """Merges a left and right fields from SPC."""
         # TODO: add implementation for any pair of fields
         pass
 
-    def merge_people_and_households(self) -> pl.DataFrame:
-        return self.people.unnest("identifiers").join(
-            self.households, left_on="household", right_on="id", how="left"
-        )
+    def merge_people_and_households(self) -> DataFrame:
+        if self.backend == "polars":
+            return self.people.unnest("identifiers").join(
+                self.households, left_on="household", right_on="id", how="left"
+            )
+        elif self.backend == "pandas":
+            # TODO: handle duplicate column names ("id")
+            return (
+                self.people.drop(columns=["identifiers"])
+                .join(pd.json_normalize(self.people["identifiers"]))
+                .merge(self.households, left_on="household", right_on="id", how="left")
+            )
+        else:
+            raise backend_error(self.backend)
 
     def merge_people_and_time_use_diaries(
         self, people_features: Dict[str, List[str]], diary_type: str = "weekday_diaries"
-    ) -> pl.DataFrame:
+    ) -> DataFrame:
         people = (
             self.people.unnest(people_features.keys())
             .select(