diff --git a/app/models/concerns/proposable.rb b/app/models/concerns/proposable.rb
index 190a1d8..77226a9 100644
--- a/app/models/concerns/proposable.rb
+++ b/app/models/concerns/proposable.rb
@@ -5,6 +5,7 @@ module Proposable
     has_one :proposition, as: :proposable, dependent: :destroy
     has_one :proposer, through: :proposition
     delegate :email, to: :proposer, prefix: true
+    scope :confirmed, -> { joins(:proposition).where.not(propositions: {confirmed_at: nil}) }
 
     Proposition.defined_enums["status"].keys.each do |status|
       scope status.to_sym, -> { joins(:proposition).where(propositions: {status: Proposition.defined_enums["status"][status]}) }
diff --git a/app/models/conference.rb b/app/models/conference.rb
index 0da4ecf..0aaecc6 100644
--- a/app/models/conference.rb
+++ b/app/models/conference.rb
@@ -32,7 +32,7 @@ class Conference < ActiveRecord::Base
   end
 
   def submissions_grouped_by_confirmation_day
-    submissions = events.approved.confirmed.group('date(events.confirmed_at)').select('date(events.confirmed_at) as confirmed_at, count(events.id) as number')
+    submissions = events.approved.confirmed.group('date(propositions.confirmed_at)').select('date(propositions.confirmed_at) as confirmed_at, count(events.id) as number')
     submissions.group_by { |s| s.confirmed_at.to_date }
   end
 
diff --git a/app/models/event.rb b/app/models/event.rb
index c33520c..35e2f61 100644
--- a/app/models/event.rb
+++ b/app/models/event.rb
@@ -24,8 +24,6 @@ class Event < ActiveRecord::Base
   validates :length, presence: true, numericality: {only_integer: true}
   validate :length_is_within_the_permitted_interval
 
-  scope :confirmed, -> { where.not confirmed_at: nil }
-
   delegate :status, to: :proposition
 
   def proposer_profile
diff --git a/db/migrate/20151018211611_add_confirmed_at_to_propositions.rb b/db/migrate/20151018211611_add_confirmed_at_to_propositions.rb
new file mode 100644
index 0000000..0b8ae5e
--- /dev/null
+++ b/db/migrate/20151018211611_add_confirmed_at_to_propositions.rb
@@ -0,0 +1,5 @@
+class AddConfirmedAtToPropositions < ActiveRecord::Migration
+  def change
+    add_column :propositions, :confirmed_at, :timestamp
+  end
+end
diff --git a/db/migrate/20151018211712_populate_confirmed_at_of_propositions_for_events.rb b/db/migrate/20151018211712_populate_confirmed_at_of_propositions_for_events.rb
new file mode 100644
index 0000000..fd54dd5
--- /dev/null
+++ b/db/migrate/20151018211712_populate_confirmed_at_of_propositions_for_events.rb
@@ -0,0 +1,17 @@
+class Event < ActiveRecord::Base
+  include Proposable
+end
+
+class PopulateConfirmedAtOfPropositionsForEvents < ActiveRecord::Migration
+  def up
+    Event.all do |event|
+      event.proposition.update(confirmed_at: event.confirmed_at)
+    end
+  end
+
+  def down
+    Event.all do |event|
+      event.update(confirmed_at: event.proposition.confirmed_at)
+    end
+  end
+end
diff --git a/db/migrate/20151018212026_remove_confirmed_at_from_events.rb b/db/migrate/20151018212026_remove_confirmed_at_from_events.rb
new file mode 100644
index 0000000..1173060
--- /dev/null
+++ b/db/migrate/20151018212026_remove_confirmed_at_from_events.rb
@@ -0,0 +1,5 @@
+class RemoveConfirmedAtFromEvents < ActiveRecord::Migration
+  def change
+    remove_column :events, :confirmed_at, :timestamp
+  end
+end