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 0.2730
Ceremonial Robe 0.2037
Spell Prism 0.2008
Quickening Charm 0.1887
Stormcrafter 0.1874
Timeless Relic 0.1607
Telescope 0.1484
Enchanted Quiver 0.1357
Seer Stone 0.1349
Psychic Headband 0.1346
Bullwhip 0.1278
Dandelion Amulet 0.1236
Titan Sliver 0.0957
Eye Of The Vizier 0.0875
Arcane Ring 0.0846
Ninja Gear 0.0828
Gossamer Cape 0.0761
Pupil'S Gift 0.0739
Ex Machina 0.0702
Defiant Shell 0.0506
Force Boots 0.0472
Mirror Shield 0.0472
Elven Tunic 0.0459
Book Of Shadows 0.0326
Trickster Cloak 0.0303
Occult Bracelet 0.0236
Grove Bow 0.0231
Fairy'S Trinket 0.0202
Mind Breaker 0.0172
Vambrace 0.0153
Paladin Sword 0.0082
Cloak Of Flames 0.0065
Arcanist'S Armor 0.0055
Faded Broach -0.0037
Ascetic'S Cap -0.0129
Penta-Edged Sword -0.0183
Ogre Seal Totem -0.0311
Book Of The Dead -0.0458
Martyr'S Plate -0.0645
Trusty Shovel -0.0769
Fallen Sky -0.0780
Havoc Hammer -0.0887
Seeds Of Serenity -0.0977
Dragon Scale -0.0987
Apex -0.1179
Philosopher'S Stone -0.1354
Lance Of Pursuit -0.1366
Stygian Desolator -0.1401
Giant'S Ring -0.1455
Tumbler'S Toy -0.1468
Vampire Fangs -0.1517
Pig Pole -0.1563
Pirate Hat -0.1803
Broom Handle -0.2745
Spark Of Courage -0.3124
Duelist Gloves -0.4497