We can always consult the league tables to find out where teams are – but are they where we expected them to be? It’s hard to avoid the idea that some teams are doing better than expected (Liverpool? Leeds?), and others are performing much worse than expected (Burnley, Millwall, Notts County). Shouldn’t tables reflect that?
Elo rankings offer such an opportunity. They give each competitor (team, individual) a strength score, from which a prediction can be generated for each match that lies between 0 and 1. In football, 0 would be an away win, 1 would be a home win, and 0.5 would represent a perfectly evenly matched event. So if our outcome variable is 0 for an away win, 0.5 for a draw, and 1 for a home win.
So we can look at every match so far this season, and see whether or not teams have exceeded expectations. If a home team had an Elo prediction of 0.45 and won, then the outcome is 1, and the Elo improvement is 1-0.45, hence positive. If on the other hand the Elo prediction was 0.7 and the visiting team won, then the home team’s adjustment would be 0-0.7, hence negative.
So teams that have consistently exceeded expectations would have a sum of adjustments that are positive, but a team that has under performed would have a sum of adjustments that is negative.
In the featured image for this post, we plot the story so far for the Premier League. Watford’s strong start is clear, and Liverpool’s seemingly relentless journey to the summit of the table on Christmas Day is there. However, up until two games ago, when Arsenal lost at Southampton, Arsenal were actually the most improve team.
Champions Manchester City are ninth placed in this table, falling from third on the eve of their match at Chelsea.
At the bottom, things are not surprising. Fulham, despite their summer investment, have struggled badly, as have Burnley following their success last season. Southampton and Crystal Palace are the two fastest improving sides at the moment.
Into the Championship, and indeed Leeds are the team most exceeding expectations, following on from their strong start, somewhat muted October, and strong November and December. Millwall are the biggest disappointment at half way.
Into Leagues One and Two (below), Macclesfield and Notts County stand out in League Two for seriously, seriously bad performances relative to expectations.