diff --git a/mlair/helpers/statistics.py b/mlair/helpers/statistics.py
index d1259a45edb2cca97595554ebe2f5990595720af..06394bb07edd95aab92b39a1fcc8a83bd63d0659 100644
--- a/mlair/helpers/statistics.py
+++ b/mlair/helpers/statistics.py
@@ -269,7 +269,6 @@ class SkillScores:
         self.external_data = external_data
         self.models = self.set_model_names(models)
         self.observation_name = observation_name
-        self.ahead_dim = ahead_dim
 
 
     def set_model_names(self, models: List[str]) -> List[str]: