Towards a New Dynamic Measure of Competitive Balance: A Study Applied to Australia's Two Major Professional 'Football' Leagues*

A new measure for competitive balance between seasons is proposed, which takes the form of a mobility gain function, based on each team's win ratios from the current and previous seasons. This 'dynamic' function measures competitive balance within a one-period change framework. While it is not suggested that this measure replace useful existing within-season measures, such as the widely used actual-to-idealised standard deviation (ASD/ISD) ratio, this measure does overcome one of the shortcomings of within-season measures - that is, the ability to pick up uncertainty of outcome from season to season, rather than merely from round-to-round. Hence, it is suggested that this measure could be used in conjunction with within-season measures in time-series analysis. An application to Australia's Australian Football League (AFL) and National Rugby League (NRL) over a century of data reveals numerous interesting comparisons.