The correlation between xpm and Win Rate is 0.72. 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
Meteor Hammer 0.1840
Guardian Greaves 0.1377
Boots Of Bearing 0.1324
Holy Locket 0.1296
Solar Crest 0.1079
Assault Cuirass 0.0861
Pipe Of Insight 0.0821
Aeon Disk 0.0812
Vladmir'S Offering 0.0741
Heart Of Tarrasque 0.0711
Moon Shard 0.0703
Octarine Core 0.0665
Shiva'S Guard 0.0635
Aether Lens 0.0552
Bloodstone 0.0545
Wind Waker 0.0543
Refresher Orb 0.0533
Lotus Orb 0.0515
Overwhelming Blink 0.0487
Glimmer Cape 0.0483
Crimson Guard 0.0441
Ethereal Blade 0.0426
Aghanim'S Scepter 0.0414
Yasha And Kaya 0.0364
Harpoon 0.0344
Kaya And Sange 0.0317
Helm Of The Overlord 0.0317
Butterfly 0.0291
Spirit Vessel 0.0277
Aghanim'S Shard 0.0269
Force Staff 0.0252
Eternal Shroud 0.0229
Drum Of Endurance 0.0225
Boots Of Travel 0.0223
Rod Of Atos 0.0212
Arcane Blink 0.0205
Mekansm 0.0191
Sange And Yasha 0.0157
Bloodthorn 0.0140
Linken'S Sphere 0.0124
Arcane Boots 0.0117
Scythe Of Vyse 0.0095
Blink Dagger 0.0085
Eul'S Scepter Of Divinity 0.0067
Eye Of Skadi 0.0028
Satanic 0.0014
Gleipnir 0.0012
Disperser 0.0001
Hurricane Pike -0.0002
Tranquil Boots -0.0004
Heaven'S Halberd -0.0033
Magic Wand -0.0050
Abyssal Blade -0.0061
Daedalus -0.0064
Radiance -0.0066
Phylactery -0.0179
Mjollnir -0.0189
Mage Slayer -0.0205
Bracer -0.0205
Swift Blink -0.0219
Null Talisman -0.0236
Armlet Of Mordiggian -0.0237
Skull Basher -0.0246
Orb Of Corrosion -0.0260
Desolator -0.0264
Phase Boots -0.0265
Aghanim'S Blessing -0.0274
Blade Mail -0.0280
Pavise -0.0297
Manta Style -0.0339
Boots Of Travel 2 -0.0358
Revenant'S Brooch -0.0362
Silver Edge -0.0370
Soul Ring -0.0374
Nullifier -0.0460
Vanguard -0.0476
Black King Bar -0.0482
Urn Of Shadows -0.0514
Bottle -0.0542
Wraith Band -0.0552
Dagon -0.0566
Orchid Malevolence -0.0570
Hand Of Midas -0.0603
Power Treads -0.0609
Witch Blade -0.0654
Falcon Blade -0.0670
Monkey King Bar -0.0694
Dragon Lance -0.0735
Helm Of The Dominator -0.0739
Echo Sabre -0.0781
Mask Of Madness -0.0849
Diffusal Blade -0.0850
Shadow Blade -0.0950
Battle Fury -0.1001
Veil Of Discord -0.1001
Crystalys -0.1043
Maelstrom -0.1577