diff --git a/CHANGELOG.md b/CHANGELOG.md
index 226f09374..8d8f539a7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -134,6 +134,7 @@
     Bug #4653: Length of non-ASCII strings is handled incorrectly in ESM reader
     Bug #4654: Editor: UpdateVisitor does not initialize skeletons for animated objects
     Bug #4668: Editor: Light source color is displayed as an integer
+    Bug #4671: knownEffect functions should use modified Alchemy skill
     Feature #912: Editor: Add missing icons to UniversalId tables
     Feature #1221: Editor: Creature/NPC rendering
     Feature #1617: Editor: Enchantment effect record verifier
diff --git a/apps/openmw/mwclass/ingredient.cpp b/apps/openmw/mwclass/ingredient.cpp
index c133b6a26..70339564c 100644
--- a/apps/openmw/mwclass/ingredient.cpp
+++ b/apps/openmw/mwclass/ingredient.cpp
@@ -14,8 +14,6 @@
 #include "../mwworld/actioneat.hpp"
 #include "../mwworld/nullaction.hpp"
 
-#include "../mwmechanics/npcstats.hpp"
-
 #include "../mwgui/tooltips.hpp"
 
 #include "../mwrender/objects.hpp"
@@ -134,8 +132,7 @@ namespace MWClass
         }
 
         MWWorld::Ptr player = MWBase::Environment::get().getWorld ()->getPlayerPtr();
-        MWMechanics::NpcStats& npcStats = player.getClass().getNpcStats (player);
-        int alchemySkill = npcStats.getSkill (ESM::Skill::Alchemy).getBase();
+        int alchemySkill = player.getClass().getSkill(player, ESM::Skill::Alchemy);
 
         static const float fWortChanceValue =
                 MWBase::Environment::get().getWorld()->getStore().get<ESM::GameSetting>().find("fWortChanceValue")->mValue.getFloat();
diff --git a/apps/openmw/mwclass/npc.cpp b/apps/openmw/mwclass/npc.cpp
index 4979db2fd..c0f6eb64f 100644
--- a/apps/openmw/mwclass/npc.cpp
+++ b/apps/openmw/mwclass/npc.cpp
@@ -949,7 +949,7 @@ namespace MWClass
         if(sneaking)
             walkSpeed *= gmst.fSneakSpeedMultiplier->mValue.getFloat();
 
-        float runSpeed = walkSpeed*(0.01f * npcdata->mNpcStats.getSkill(ESM::Skill::Athletics).getModified() *
+        float runSpeed = walkSpeed*(0.01f * getSkill(ptr, ESM::Skill::Athletics) *
                                     gmst.fAthleticsRunBonus->mValue.getFloat() + gmst.fBaseRunMultiplier->mValue.getFloat());
 
         float moveSpeed;
@@ -971,7 +971,7 @@ namespace MWClass
             if(running)
                 swimSpeed = runSpeed;
             swimSpeed *= 1.0f + 0.01f * mageffects.get(ESM::MagicEffect::SwiftSwim).getMagnitude();
-            swimSpeed *= gmst.fSwimRunBase->mValue.getFloat() + 0.01f*npcdata->mNpcStats.getSkill(ESM::Skill::Athletics).getModified()*
+            swimSpeed *= gmst.fSwimRunBase->mValue.getFloat() + 0.01f*getSkill(ptr, ESM::Skill::Athletics)*
                                                     gmst.fSwimRunAthleticsMult->mValue.getFloat();
             moveSpeed = swimSpeed;
         }
@@ -1004,7 +1004,7 @@ namespace MWClass
                                           gmst.fJumpEncumbranceMultiplier->mValue.getFloat() *
                                           (1.0f - Npc::getNormalizedEncumbrance(ptr));
 
-        float a = static_cast<float>(npcdata->mNpcStats.getSkill(ESM::Skill::Acrobatics).getModified());
+        float a = static_cast<float>(getSkill(ptr, ESM::Skill::Acrobatics));
         float b = 0.0f;
         if(a > 50.0f)
         {
@@ -1129,7 +1129,7 @@ namespace MWClass
 
         float fUnarmoredBase1 = store.find("fUnarmoredBase1")->mValue.getFloat();
         float fUnarmoredBase2 = store.find("fUnarmoredBase2")->mValue.getFloat();
-        int unarmoredSkill = stats.getSkill(ESM::Skill::Unarmored).getModified();
+        int unarmoredSkill = getSkill(ptr, ESM::Skill::Unarmored);
 
         float ratings[MWWorld::InventoryStore::Slots];
         for(int i = 0;i < MWWorld::InventoryStore::Slots;i++)
diff --git a/apps/openmw/mwgui/recharge.cpp b/apps/openmw/mwgui/recharge.cpp
index a6ed16bd4..672db3e32 100644
--- a/apps/openmw/mwgui/recharge.cpp
+++ b/apps/openmw/mwgui/recharge.cpp
@@ -18,7 +18,6 @@
 #include "../mwworld/esmstore.hpp"
 
 #include "../mwmechanics/creaturestats.hpp"
-#include "../mwmechanics/npcstats.hpp"
 #include "../mwmechanics/actorutil.hpp"
 
 #include "itemwidget.hpp"
@@ -139,7 +138,6 @@ void Recharge::onItemClicked(MyGUI::Widget *sender, const MWWorld::Ptr& item)
 
     MWWorld::Ptr player = MWMechanics::getPlayer();
     MWMechanics::CreatureStats& stats = player.getClass().getCreatureStats(player);
-    MWMechanics::NpcStats& npcStats = player.getClass().getNpcStats(player);
 
     float luckTerm = 0.1f * stats.getAttribute(ESM::Attribute::Luck).getModified();
     if (luckTerm < 1|| luckTerm > 10)
@@ -152,7 +150,7 @@ void Recharge::onItemClicked(MyGUI::Widget *sender, const MWWorld::Ptr& item)
     if (intelligenceTerm < 1)
         intelligenceTerm = 1;
 
-    float x = (npcStats.getSkill(ESM::Skill::Enchant).getModified() + intelligenceTerm + luckTerm) * stats.getFatigueTerm();
+    float x = (player.getClass().getSkill(player, ESM::Skill::Enchant) + intelligenceTerm + luckTerm) * stats.getFatigueTerm();
     int roll = Misc::Rng::roll0to99();
     if (roll < x)
     {
diff --git a/apps/openmw/mwgui/trainingwindow.cpp b/apps/openmw/mwgui/trainingwindow.cpp
index b309da27d..60e6584c7 100644
--- a/apps/openmw/mwgui/trainingwindow.cpp
+++ b/apps/openmw/mwgui/trainingwindow.cpp
@@ -73,14 +73,12 @@ namespace MWGui
 
         mPlayerGold->setCaptionWithReplacing("#{sGold}: " + MyGUI::utility::toString(playerGold));
 
-        MWMechanics::NpcStats& npcStats = actor.getClass().getNpcStats (actor);
-
         // NPC can train you in his best 3 skills
         std::vector< std::pair<int, int> > skills;
 
         for (int i=0; i<ESM::Skill::Length; ++i)
         {
-            int value = npcStats.getSkill (i).getModified ();
+            int value = actor.getClass().getSkill(actor, i);
 
             skills.push_back(std::make_pair(i, value));
         }
@@ -142,8 +140,7 @@ namespace MWGui
         if (price > player.getClass().getContainerStore(player).count(MWWorld::ContainerStore::sGoldId))
             return;
 
-        MWMechanics::NpcStats& npcStats = mPtr.getClass().getNpcStats (mPtr);
-        if (npcStats.getSkill (skillId).getModified () <= pcStats.getSkill (skillId).getBase ())
+        if (mPtr.getClass().getSkill(mPtr, skillId) <= pcStats.getSkill (skillId).getBase ())
         {
             MWBase::Environment::get().getWindowManager()->messageBox ("#{sServiceTrainingWords}");
             return;
@@ -168,6 +165,7 @@ namespace MWGui
         player.getClass().getContainerStore(player).remove(MWWorld::ContainerStore::sGoldId, price, player);
 
         // add gold to NPC trading gold pool
+        MWMechanics::NpcStats& npcStats = mPtr.getClass().getNpcStats(mPtr);
         npcStats.setGoldPool(npcStats.getGoldPool() + price);
 
         // advance time
diff --git a/apps/openmw/mwmechanics/alchemy.cpp b/apps/openmw/mwmechanics/alchemy.cpp
index 98860198b..c199bfb3f 100644
--- a/apps/openmw/mwmechanics/alchemy.cpp
+++ b/apps/openmw/mwmechanics/alchemy.cpp
@@ -26,7 +26,6 @@
 
 #include "magiceffects.hpp"
 #include "creaturestats.hpp"
-#include "npcstats.hpp"
 
 MWMechanics::Alchemy::Alchemy()
     : mValue(0)
@@ -318,10 +317,9 @@ void MWMechanics::Alchemy::increaseSkill()
 float MWMechanics::Alchemy::getAlchemyFactor() const
 {
     const CreatureStats& creatureStats = mAlchemist.getClass().getCreatureStats (mAlchemist);
-    const NpcStats& npcStats = mAlchemist.getClass().getNpcStats (mAlchemist);
 
     return
-        (npcStats.getSkill (ESM::Skill::Alchemy).getModified() +
+        (mAlchemist.getClass().getSkill(mAlchemist, ESM::Skill::Alchemy) +
         0.1f * creatureStats.getAttribute (ESM::Attribute::Intelligence).getModified()
         + 0.1f * creatureStats.getAttribute (ESM::Attribute::Luck).getModified());
 }
@@ -472,8 +470,7 @@ MWMechanics::Alchemy::TEffectsIterator MWMechanics::Alchemy::endEffects() const
 
 bool MWMechanics::Alchemy::knownEffect(unsigned int potionEffectIndex, const MWWorld::Ptr &npc)
 {
-    MWMechanics::NpcStats& npcStats = npc.getClass().getNpcStats(npc);
-    int alchemySkill = npcStats.getSkill (ESM::Skill::Alchemy).getBase();
+    int alchemySkill = npc.getClass().getSkill (npc, ESM::Skill::Alchemy);
     static const float fWortChanceValue =
             MWBase::Environment::get().getWorld()->getStore().get<ESM::GameSetting>().find("fWortChanceValue")->mValue.getFloat();
     return (potionEffectIndex <= 1 && alchemySkill >= fWortChanceValue)
diff --git a/apps/openmw/mwmechanics/enchanting.cpp b/apps/openmw/mwmechanics/enchanting.cpp
index c0bffc4cb..e4bb0cf3f 100644
--- a/apps/openmw/mwmechanics/enchanting.cpp
+++ b/apps/openmw/mwmechanics/enchanting.cpp
@@ -10,7 +10,6 @@
 #include "../mwbase/mechanicsmanager.hpp"
 
 #include "creaturestats.hpp"
-#include "npcstats.hpp"
 #include "spellcasting.hpp"
 #include "actorutil.hpp"
 
@@ -280,11 +279,11 @@ namespace MWMechanics
 
     float Enchanting::getEnchantChance() const
     {
-        const NpcStats& npcStats = mEnchanter.getClass().getNpcStats (mEnchanter);
+        const CreatureStats& stats = mEnchanter.getClass().getCreatureStats(mEnchanter);
 
-        float chance1 = (npcStats.getSkill (ESM::Skill::Enchant).getModified() + 
-        (0.25f * npcStats.getAttribute (ESM::Attribute::Intelligence).getModified())
-        + (0.125f * npcStats.getAttribute (ESM::Attribute::Luck).getModified()));
+        float chance1 = (mEnchanter.getClass().getSkill(mEnchanter, ESM::Skill::Enchant) + 
+        (0.25f * stats.getAttribute (ESM::Attribute::Intelligence).getModified())
+        + (0.125f * stats.getAttribute (ESM::Attribute::Luck).getModified()));
 
         const MWWorld::Store<ESM::GameSetting>& gmst = MWBase::Environment::get().getWorld()->getStore().get<ESM::GameSetting>();
 
diff --git a/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp b/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp
index 33357b79a..1ea40023b 100644
--- a/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp
+++ b/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp
@@ -639,10 +639,10 @@ namespace MWMechanics
         // I suppose the temporary disposition change (second param to getDerivedDisposition()) _has_ to be considered here,
         // otherwise one would get different prices when exiting and re-entering the dialogue window...
         int clampedDisposition = getDerivedDisposition(ptr);
-        float a = static_cast<float>(std::min(playerStats.getSkill(ESM::Skill::Mercantile).getModified(), 100));
+        float a = static_cast<float>(std::min(playerPtr.getClass().getSkill(playerPtr, ESM::Skill::Mercantile), 100));
         float b = std::min(0.1f * playerStats.getAttribute(ESM::Attribute::Luck).getModified(), 10.f);
         float c = std::min(0.2f * playerStats.getAttribute(ESM::Attribute::Personality).getModified(), 10.f);
-        float d = static_cast<float>(std::min(sellerStats.getSkill(ESM::Skill::Mercantile).getModified(), 100));
+        float d = static_cast<float>(std::min(ptr.getClass().getSkill(ptr, ESM::Skill::Mercantile), 100));
         float e = std::min(0.1f * sellerStats.getAttribute(ESM::Attribute::Luck).getModified(), 10.f);
         float f = std::min(0.2f * sellerStats.getAttribute(ESM::Attribute::Personality).getModified(), 10.f);
         float pcTerm = (clampedDisposition - 50 + a + b + c) * playerStats.getFatigueTerm();
diff --git a/apps/openmw/mwmechanics/repair.cpp b/apps/openmw/mwmechanics/repair.cpp
index 3ebef36bf..8c5e69896 100644
--- a/apps/openmw/mwmechanics/repair.cpp
+++ b/apps/openmw/mwmechanics/repair.cpp
@@ -14,7 +14,6 @@
 #include "../mwworld/esmstore.hpp"
 
 #include "creaturestats.hpp"
-#include "npcstats.hpp"
 #include "actorutil.hpp"
 
 namespace MWMechanics
@@ -34,12 +33,11 @@ void Repair::repair(const MWWorld::Ptr &itemToRepair)
     mTool.getCellRef().setCharge(uses-1);
 
     MWMechanics::CreatureStats& stats = player.getClass().getCreatureStats(player);
-    MWMechanics::NpcStats& npcStats = player.getClass().getNpcStats(player);
 
     float fatigueTerm = stats.getFatigueTerm();
     int pcStrength = stats.getAttribute(ESM::Attribute::Strength).getModified();
     int pcLuck = stats.getAttribute(ESM::Attribute::Luck).getModified();
-    int armorerSkill = npcStats.getSkill(ESM::Skill::Armorer).getModified();
+    int armorerSkill = player.getClass().getSkill(player, ESM::Skill::Armorer);
 
     float fRepairAmountMult = MWBase::Environment::get().getWorld()->getStore().get<ESM::GameSetting>()
             .find("fRepairAmountMult")->mValue.getFloat();
diff --git a/apps/openmw/mwmechanics/security.cpp b/apps/openmw/mwmechanics/security.cpp
index c8a4dd770..18d4ec2e5 100644
--- a/apps/openmw/mwmechanics/security.cpp
+++ b/apps/openmw/mwmechanics/security.cpp
@@ -11,7 +11,6 @@
 #include "../mwbase/windowmanager.hpp"
 #include "../mwbase/mechanicsmanager.hpp"
 
-#include "npcstats.hpp"
 #include "creaturestats.hpp"
 
 namespace MWMechanics
@@ -21,10 +20,9 @@ namespace MWMechanics
         : mActor(actor)
     {
         CreatureStats& creatureStats = actor.getClass().getCreatureStats(actor);
-        NpcStats& npcStats = actor.getClass().getNpcStats(actor);
         mAgility = static_cast<float>(creatureStats.getAttribute(ESM::Attribute::Agility).getModified());
         mLuck = static_cast<float>(creatureStats.getAttribute(ESM::Attribute::Luck).getModified());
-        mSecuritySkill = static_cast<float>(npcStats.getSkill(ESM::Skill::Security).getModified());
+        mSecuritySkill = static_cast<float>(actor.getClass().getSkill(actor, ESM::Skill::Security));
         mFatigueTerm = creatureStats.getFatigueTerm();
     }
 
diff --git a/apps/openmw/mwmechanics/spellcasting.cpp b/apps/openmw/mwmechanics/spellcasting.cpp
index f1ee2520b..f6eb497e7 100644
--- a/apps/openmw/mwmechanics/spellcasting.cpp
+++ b/apps/openmw/mwmechanics/spellcasting.cpp
@@ -964,10 +964,9 @@ namespace MWMechanics
             MWBase::Environment::get().getWorld()->getStore().get<ESM::MagicEffect>().find (
             effect.mEffectID);
 
-        const MWMechanics::NpcStats& npcStats = mCaster.getClass().getNpcStats(mCaster);
         const MWMechanics::CreatureStats& creatureStats = mCaster.getClass().getCreatureStats(mCaster);
 
-        float x = (npcStats.getSkill (ESM::Skill::Alchemy).getModified() +
+        float x = (mCaster.getClass().getSkill(mCaster, ESM::Skill::Alchemy) +
                     0.2f * creatureStats.getAttribute (ESM::Attribute::Intelligence).getModified()
                     + 0.1f * creatureStats.getAttribute (ESM::Attribute::Luck).getModified())
                     * creatureStats.getFatigueTerm();
diff --git a/apps/openmw/mwmechanics/spellpriority.cpp b/apps/openmw/mwmechanics/spellpriority.cpp
index 807b56608..3b242266c 100644
--- a/apps/openmw/mwmechanics/spellpriority.cpp
+++ b/apps/openmw/mwmechanics/spellpriority.cpp
@@ -14,7 +14,7 @@
 #include "../mwworld/actionequip.hpp"
 #include "../mwworld/cellstore.hpp"
 
-#include "npcstats.hpp"
+#include "creaturestats.hpp"
 #include "spellcasting.hpp"
 #include "combat.hpp"
 
@@ -538,7 +538,7 @@ namespace MWMechanics
         case ESM::MagicEffect::DrainSkill:
             if (enemy.isEmpty() || !enemy.getClass().isNpc())
                 return 0.f;
-            if (enemy.getClass().getNpcStats(enemy).getSkill(effect.mSkill).getModified() <= 0)
+            if (enemy.getClass().getSkill(enemy, effect.mSkill) <= 0)
                 return 0.f;
             break;
 
diff --git a/apps/openmw/mwworld/inventorystore.cpp b/apps/openmw/mwworld/inventorystore.cpp
index 7f3018c55..59ec6ab3e 100644
--- a/apps/openmw/mwworld/inventorystore.cpp
+++ b/apps/openmw/mwworld/inventorystore.cpp
@@ -250,11 +250,10 @@ void MWWorld::InventoryStore::autoEquip (const MWWorld::Ptr& actor)
 {
     const MWBase::World *world = MWBase::Environment::get().getWorld();
     const MWWorld::Store<ESM::GameSetting> &store = world->getStore().get<ESM::GameSetting>();
-    MWMechanics::NpcStats& stats = actor.getClass().getNpcStats(actor);
 
     static float fUnarmoredBase1 = store.find("fUnarmoredBase1")->mValue.getFloat();
     static float fUnarmoredBase2 = store.find("fUnarmoredBase2")->mValue.getFloat();
-    int unarmoredSkill = stats.getSkill(ESM::Skill::Unarmored).getModified();
+    int unarmoredSkill = actor.getClass().getSkill(actor, ESM::Skill::Unarmored);
 
     float unarmoredRating = (fUnarmoredBase1 * unarmoredSkill) * (fUnarmoredBase2 * unarmoredSkill);
 
@@ -384,7 +383,7 @@ void MWWorld::InventoryStore::autoEquip (const MWWorld::Ptr& actor)
 
         for (int j = 0; j < static_cast<int>(weaponSkillsLength); ++j)
         {
-            int skillValue = stats.getSkill(static_cast<int>(weaponSkills[j])).getModified();
+            int skillValue = actor.getClass().getSkill(actor, static_cast<int>(weaponSkills[j]));
 
             if (skillValue > max && !weaponSkillVisited[j])
             {