The correlation between xpm and Win Rate is 0.7. 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
Holy Locket 0.1394
Boots Of Bearing 0.1391
Guardian Greaves 0.1266
Vladmir'S Offering 0.0930
Pavise 0.0815
Wind Waker 0.0805
Aeon Disk 0.0784
Solar Crest 0.0745
Overwhelming Blink 0.0734
Moon Shard 0.0720
Assault Cuirass 0.0704
Meteor Hammer 0.0685
Octarine Core 0.0656
Pipe Of Insight 0.0643
Lotus Orb 0.0613
Heart Of Tarrasque 0.0607
Spirit Vessel 0.0586
Aether Lens 0.0563
Refresher Orb 0.0562
Yasha And Kaya 0.0528
Glimmer Cape 0.0513
Shiva'S Guard 0.0492
Arcane Blink 0.0471
Revenant'S Brooch 0.0468
Veil Of Discord 0.0464
Boots Of Travel 0.0405
Aghanim'S Scepter 0.0398
Crimson Guard 0.0386
Phylactery 0.0385
Helm Of The Overlord 0.0381
Force Staff 0.0370
Dagon (5) 0.0343
Scythe Of Vyse 0.0341
Aghanim'S Shard 0.0302
Boots Of Travel 2 0.0291
Ethereal Blade 0.0291
Bloodthorn 0.0289
Rod Of Atos 0.0284
Butterfly 0.0275
Bloodstone 0.0211
Eul'S Scepter Of Divinity 0.0204
Aghanim'S Blessing 0.0192
Eye Of Skadi 0.0150
Gleipnir 0.0133
Drum Of Endurance 0.0130
Harpoon 0.0123
Linken'S Sphere 0.0118
Tranquil Boots 0.0102
Swift Blink 0.0065
Satanic 0.0048
Kaya And Sange 0.0042
Arcane Boots 0.0023
Disperser 0.0018
Abyssal Blade 0.0014
Eternal Shroud -0.0012
Daedalus -0.0013
Hurricane Pike -0.0014
Magic Wand -0.0014
Dagon (4) -0.0053
Heaven'S Halberd -0.0054
Sange And Yasha -0.0082
Blink Dagger -0.0094
Null Talisman -0.0177
Nullifier -0.0179
Mjollnir -0.0208
Mekansm -0.0209
Urn Of Shadows -0.0251
Bracer -0.0251
Radiance -0.0288
Desolator -0.0300
Blade Mail -0.0303
Soul Ring -0.0313
Dagon (3) -0.0361
Witch Blade -0.0364
Manta Style -0.0375
Orb Of Corrosion -0.0457
Phase Boots -0.0467
Silver Edge -0.0482
Armlet Of Mordiggian -0.0513
Orchid Malevolence -0.0530
Dagon (2) -0.0584
Dagon -0.0589
Mage Slayer -0.0607
Skull Basher -0.0615
Monkey King Bar -0.0620
Falcon Blade -0.0625
Black King Bar -0.0635
Medallion Of Courage -0.0665
Power Treads -0.0682
Vanguard -0.0702
Wraith Band -0.0715
Bottle -0.0743
Diffusal Blade -0.0814
Hand Of Midas -0.0817
Dragon Lance -0.0824
Helm Of The Dominator -0.0859
Echo Sabre -0.0933
Mask Of Madness -0.1021
Shadow Blade -0.1160
Crystalys -0.1165
Battle Fury -0.1175
Maelstrom -0.1542