The Bartle taxonomy of player types is a classification of video game players (gamers) based on a 1996 paper by Richard Bartle according to their preferred actions within the game. The classification originally described players of multiplayer online games (including MUDs and MMORPGs), though now it also refers to players of single-player video games. The taxonomy is based on a character theory. This character theory consists of four characters: Achievers, Explorers, Socializers, and Killers. These are imagined according to a quadrant model where the X axis represents preference for interacting with other players vs. exploring the world and the Y axis represents preference for interaction vs. unilateral action. A test known as Bartle Test of Gamer Psychology based on Bartle's taxonomy was created in 1999–2000 by Erwin Andreasen and Brandon Downey, containing a series of questions and an accompanying scoring formula. Although the test has met with some criticism for the dichotomous nature of its question-asking method, as of October 2011, it had been taken over 800,000 times. As of February 2018, the Bartle Test of Gamer Psychology hosted by GamerDNA is no longer available. Alternative online implementations of the test exist, however. The result of the Bartle Test is the "Bartle Quotient", which is calculated based on the answers to a series of 30 random questions in the test, and totals 200% across all categories, with no single category exceeding 100%. Achievers Also known as "Diamonds" (♦) , these are players who prefer to gain "points", levels, equipment and other concrete measurements of succeeding in a game. They will go to great lengths to achieve rewards that are merely cosmetic. Single-player appeal to the Achiever Every game that can be "beaten" in some way caters to the Achiever play style by giving them something to accomplish. Games that offer a 100% completion rating appeal to Achievers. Multi-player appeal to the Achiever One of the appeals of online gaming to the Achiever is that they have the opportunity to show off their skill and hold elite status to others. They value (or despise) the competition from other Achievers, and look to the Socializers to give them praise. Microsoft's Xbox Live utilizes the Gamerscore to reward Achievers, who can get points by completing difficult "Achievements" in the various games they purchase. They can, in turn, compare themselves to other gamers from around the world. Explorers Explorers, dubbed "Spades" (♠) for their