The correlation between xpm and Win Rate is 0.79. The more xpm, 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 xpm (blue dots) with respect to the expected value (red line).
Efficiency
Stormcrafter 0.0490
Book Of The Dead 0.0443
Arcanist'S Armor 0.0385
Telescope 0.0379
Arcane Ring 0.0346
Ceremonial Robe 0.0330
Bullwhip 0.0270
Spell Prism 0.0216
Ring Of Aquila 0.0210
Timeless Relic 0.0201
Occult Bracelet 0.0158
Quickening Charm 0.0154
Trusty Shovel 0.0151
Giant'S Ring 0.0116
Eye Of The Vizier 0.0113
Psychic Headband 0.0111
Seeds Of Serenity 0.0109
Dandelion Amulet 0.0099
Seer Stone 0.0093
Force Boots 0.0086
Faded Broach 0.0069
Ascetic'S Cap 0.0051
Gossamer Cape 0.0046
Mirror Shield 0.0035
Fairy'S Trinket 0.0022
Defiant Shell 0.0016
Cloak Of Flames -0.0008
Pupil'S Gift -0.0025
Ninja Gear -0.0042
Apex -0.0045
Stygian Desolator -0.0065
Book Of Shadows -0.0078
Martyr'S Plate -0.0081
Tumbler'S Toy -0.0096
Grove Bow -0.0098
Pirate Hat -0.0099
Mind Breaker -0.0104
Vambrace -0.0112
Pig Pole -0.0115
Enchanted Quiver -0.0117
Dragon Scale -0.0122
Havoc Hammer -0.0134
Fallen Sky -0.0137
Lance Of Pursuit -0.0143
Trickster Cloak -0.0153
Penta-Edged Sword -0.0158
Titan Sliver -0.0170
Philosopher'S Stone -0.0192
Ex Machina -0.0193
Paladin Sword -0.0200
Vampire Fangs -0.0235
Elven Tunic -0.0251
Ogre Seal Totem -0.0260
Broom Handle -0.0324
Spark Of Courage -0.0337
Duelist Gloves -0.0606