The correlation between Tier and Win Rate is 0.85. The more Tier, the more Win Rate, and vice versa. But some values are higher than expected, some are lower. Efficiency is a difference between the value of Win Rate depending on Tier (blue dots) with respect to the expected value (red line).
Efficiency
Stormcrafter 0.0495
Mind Breaker 0.0298
Arcane Ring 0.0281
Ceremonial Robe 0.0267
Ring Of Aquila 0.0221
Telescope 0.0204
Bullwhip 0.0175
Seeds Of Serenity 0.0168
Book Of The Dead 0.0156
Timeless Relic 0.0155
Arcanist'S Armor 0.0151
Defiant Shell 0.0146
Spell Prism 0.0144
Trusty Shovel 0.0136
Ascetic'S Cap 0.0126
Cloak Of Flames 0.0104
Quickening Charm 0.0102
Penta-Edged Sword 0.0098
Occult Bracelet 0.0069
Paladin Sword 0.0067
Dandelion Amulet 0.0053
Grove Bow 0.0037
Giant'S Ring 0.0036
Fairy'S Trinket 0.0027
Ninja Gear 0.0009
Enchanted Quiver 0.0003
Psychic Headband -0.0003
Havoc Hammer -0.0017
Titan Sliver -0.0017
Gossamer Cape -0.0018
Dragon Scale -0.0022
Stygian Desolator -0.0034
Martyr'S Plate -0.0035
Mirror Shield -0.0037
Force Boots -0.0040
Eye Of The Vizier -0.0042
Faded Broach -0.0053
Elven Tunic -0.0053
Pupil'S Gift -0.0067
Lance Of Pursuit -0.0079
Vampire Fangs -0.0091
Apex -0.0095
Pig Pole -0.0129
Spark Of Courage -0.0132
Pirate Hat -0.0136
Tumbler'S Toy -0.0156
Broom Handle -0.0175
Trickster Cloak -0.0181
Seer Stone -0.0188
Vambrace -0.0191
Fallen Sky -0.0213
Ex Machina -0.0252
Ogre Seal Totem -0.0255
Philosopher'S Stone -0.0301
Duelist Gloves -0.0331
Book Of Shadows -0.0380