Introduction to Elo

In the rest of this chapter, and in some of the following chapters, we are going to be working with the Elo Rating System to develop player ratings and predict match outcomes. The algorithm itself is quite simple and it will allow us to demonstrate how Clojure can be used as a data analysis tool. Since we'll be referring to it a lot, it's worth taking a closer look at how it works. The Elo Rating System was developed by Arpad Elo to rate chess players. The United States Chess Federation began using it in 1960.

Elo ratings work by establishing a score for each player. This score is used to calculate the probable outcome of a match. When the real outcome of the match is known, a player's rating is raised or lowered depending on their performance relative to the probable outcome. In other words, if a beginner with a low rating loses to a higher-rated player, the beginner's rating will not suffer by much, since that outcome was expected. If they...