diff --git a/app/controllers/stats_controller.rb b/app/controllers/stats_controller.rb
index 54cce84a2..86688ae12 100644
--- a/app/controllers/stats_controller.rb
+++ b/app/controllers/stats_controller.rb
@@ -275,28 +275,34 @@ class StatsController < ApplicationController
 
     processed_dossiers = dossiers
       .where(:processed_at => min_date..max_date)
-      .pluck(:procedure_id, :created_at, :en_construction_at, :processed_at)
+      .pluck(
+        :procedure_id,
+        Arel.sql('EXTRACT(EPOCH FROM (en_construction_at - created_at)) / 60 AS processing_time'),
+        :processed_at
+      )
 
     # Group dossiers by month
     processed_dossiers_by_month = processed_dossiers
-      .group_by do |e|
-        e[3].beginning_of_month.to_s
+      .group_by do |(*_, processed_at)|
+        processed_at.beginning_of_month.to_s
       end
 
-    processed_dossiers_by_month.map do |month, value|
+    procedure_id_type_de_champs_count = TypeDeChamp
+      .where(private: false)
+      .group(:procedure_id)
+      .count
+
+    processed_dossiers_by_month.map do |month, dossier_plucks|
       # Group the dossiers for this month by procedure
-      dossiers_grouped_by_procedure = value.group_by { |dossier| dossier[0] }
+      dossiers_grouped_by_procedure = dossier_plucks.group_by { |(procedure_id, *_)| procedure_id }
 
       # Compute the mean time for this procedure
       procedure_processing_times = dossiers_grouped_by_procedure.map do |procedure_id, procedure_dossiers|
-        procedure_dossiers_processing_time = procedure_dossiers.map do |dossier|
-          (dossier[2] - dossier[1]).to_f / 60
-        end
-
+        procedure_dossiers_processing_time = procedure_dossiers.map { |_, processing_time, _| processing_time }
         procedure_mean = mean(procedure_dossiers_processing_time)
 
         # We normalize the data for 24 fields
-        procedure_fields_count = Procedure.find(procedure_id).types_de_champ.count
+        procedure_fields_count = procedure_id_type_de_champs_count[procedure_id]
         procedure_mean * (MEAN_NUMBER_OF_CHAMPS_IN_A_FORM / procedure_fields_count)
       end