The correlation between gpm and kda is 0.89. The more gpm, 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 gpm (blue dots) with respect to the expected value (red line).
Efficiency
Ring Of Aquila 0.2547
Ceremonial Robe 0.2055
Quickening Charm 0.1936
Stormcrafter 0.1870
Spell Prism 0.1776
Timeless Relic 0.1697
Seer Stone 0.1407
Bullwhip 0.1332
Telescope 0.1282
Psychic Headband 0.1256
Dandelion Amulet 0.1214
Enchanted Quiver 0.1087
Defiant Shell 0.0936
Gossamer Cape 0.0767
Titan Sliver 0.0752
Eye Of The Vizier 0.0637
Pupil'S Gift 0.0633
Ex Machina 0.0632
Arcane Ring 0.0578
Force Boots 0.0505
Mirror Shield 0.0476
Cloak Of Flames 0.0469
Book Of Shadows 0.0399
Elven Tunic 0.0331
Ninja Gear 0.0281
Ascetic'S Cap 0.0247
Mind Breaker 0.0241
Arcanist'S Armor 0.0204
Trickster Cloak 0.0164
Ogre Seal Totem 0.0135
Paladin Sword 0.0121
Grove Bow -0.0003
Fairy'S Trinket -0.0095
Penta-Edged Sword -0.0190
Vambrace -0.0235
Book Of The Dead -0.0364
Dragon Scale -0.0450
Seeds Of Serenity -0.0502
Martyr'S Plate -0.0508
Havoc Hammer -0.0512
Occult Bracelet -0.0556
Fallen Sky -0.0604
Trusty Shovel -0.0702
Faded Broach -0.0759
Giant'S Ring -0.1164
Apex -0.1247
Philosopher'S Stone -0.1380
Vampire Fangs -0.1475
Lance Of Pursuit -0.1525
Tumbler'S Toy -0.1570
Pig Pole -0.1676
Stygian Desolator -0.1799
Pirate Hat -0.1860
Broom Handle -0.2497
Spark Of Courage -0.2515
Duelist Gloves -0.3777