G-Elo: Generalization of the Elo algorithm by modelling the discretized margin of victory

TL;DR

G-Elo extends the traditional Elo rating system by incorporating the discretized margin of victory, providing a more nuanced and probabilistic approach to rating teams based on game point differences.

Contribution

It introduces a probabilistic model for discretized margin of victory and derives a simple, transparent online rating algorithm with coefficients estimated from historical data.

Findings

Numerical examples demonstrate the effectiveness of G-Elo in football and American football.

The algorithm generalizes Elo by modeling the margin of victory probabilistically.

Coefficients are estimated in a closed-form, enabling transparent and sport-specific customization.

Abstract

In this work we develop a new algorithm for rating of teams (or players) in one-on-one games by exploiting the observed difference of the game-points (such as goals), also known as a margin of victory (MOV). Our objective is to obtain the Elo-style algorithm whose operation is simple to implement and to understand intuitively. This is done in three steps: first, we define the probabilistic model between the teams' skills and the discretized MOV variable: this generalizes the model underpinning the Elo algorithm, where the MOV variable is discretized into three categories (win/loss/draw). Second, with the formal probabilistic model at hand, the optimization required by the maximum likelihood rule is implemented via stochastic gradient; this yields simple on-line equations for the rating updates which are identical in their general form to those characteristic of the Elo algorithm: the main difference lies in the way the scores and the expected scores are defined. Third, we propose a simple method to estimate the coefficients of the model, and thus define the operation of the algorithm; it is done in a closed form using the historical data so the algorithm is tailored to the sport of interest and the coefficients defining its operation are determined in entirely transparent manner. The alternative, optimization-based strategy to find the coefficients is also presented. We show numerical examples based on the results of the association football of the English Premier League and the American football of the National Football League.