Parity and Predictability of Competitions

TL;DR

This paper analyzes sports league results to quantify team parity and game predictability, introducing a mathematical model that links upset frequency with league competitiveness.

Contribution

It presents a novel model connecting team parity and game predictability, enabling estimation of upset frequency from standings data.

Findings

Parity varies across leagues as shown by winning fraction variance.

Upset frequency correlates with league competitiveness.

The model accurately estimates upset probability from standings.

Abstract

We present an extensive statistical analysis of the results of all sports competitions in five major sports leagues in England and the United States. We characterize the parity among teams by the variance in the winning fraction from season-end standings data and quantify the predictability of games by the frequency of upsets from game results data. We introduce a novel mathematical model in which the underdog team wins with a fixed upset probability. This model quantitatively relates the parity among teams with the predictability of the games, and it can be used to estimate the upset frequency from standings data.