diff --git a/src/model/validity.py b/src/model/validity.py
index d493fb5..f3922d5 100644
--- a/src/model/validity.py
+++ b/src/model/validity.py
@@ -19,9 +19,15 @@ def _combined_validities(
         return
     combined = 0.0
     for study in apply_to.split(";"):
+        if study not in by_intervention["citation"].unique():
+            print(
+                f"WARNING: Findings table {study} study did not match any study in interventions dataframe!"
+            )
         new = by_intervention.loc[by_intervention["citation"] == study, column]
-        if len(new) > 0 and not math.isnan(new.iat[0]):
-            combined += new.iat[0]
+        if len(new) == 0 or math.isnan(new.iat[0]):
+            continue
+        combined += new.iat[0]
+
     if combined:
         return _binned_strength(combined)
     return r"\-"