The correlation between Tier and kda is 0.88. The more Tier, the more kda, and vice versa. But some values are higher than expected, some are lower. Efficiency is a difference between the value of kda depending on Tier (blue dots) with respect to the expected value (red line).
Efficiency
Mind Breaker 0.3212
Enchanted Quiver 0.2212
Paladin Sword 0.2112
Elven Tunic 0.1712
Grove Bow 0.1580
Defiant Shell 0.1512
Stormcrafter 0.1444
Ninja Gear 0.1444
Force Boots 0.1177
Arcane Ring 0.1048
Bullwhip 0.0880
Pupil'S Gift 0.0780
Cloak Of Flames 0.0712
Seeds Of Serenity 0.0648
Ceremonial Robe 0.0612
Mirror Shield 0.0477
Vampire Fangs 0.0380
Vambrace 0.0380
Dragon Scale 0.0380
Stygian Desolator 0.0377
Pirate Hat 0.0277
Timeless Relic 0.0244
Fairy'S Trinket 0.0048
Gossamer Cape -0.0020
Ascetic'S Cap -0.0056
Apex -0.0123
Occult Bracelet -0.0152
Dandelion Amulet -0.0188
Trickster Cloak -0.0256
Havoc Hammer -0.0256
Ogre Seal Totem -0.0488
Eye Of The Vizier -0.0520
Trusty Shovel -0.0552
Faded Broach -0.0652
Giant'S Ring -0.0823
Broom Handle -0.0852
Psychic Headband -0.0888
Arcanist'S Armor -0.0923
Lance Of Pursuit -0.0952
Pig Pole -0.1052
Martyr'S Plate -0.1256
Seer Stone -0.1423
Spark Of Courage -0.1452
Telescope -0.1456
Book Of Shadows -0.2023
Philosopher'S Stone -0.2320
Duelist Gloves -0.2452
Book Of The Dead -0.2523