Now that we’re at the end of the season, I thought that it was about time I updated the long-term trend graphics to see how each club fared throughout their last two-and-a-bit seasons. These are explained in full here and briefly below.

Explanation

These are adapted from a very similar design by the excellent Swedish blogger Zorba138 intended to track a club’s long-term performance and whether this was an underachievement or an overachievement based on the balance of chances created.

There are two lines:

1. The blue line shows the rolling average of a club’s goal difference over the last 10 league games;
2. The red line shows the rolling average of their expected goal difference, based on the quality of chances they’ve created and faced.

Comparing these two allows us to see not only how a club’s performances have changed over time, but also whether there were any differences between the balance of chances created (a useful measure of underlying performance) and goals scored.

These are shaded as follows:

• Blue shaded areas are where goal difference is higher than chances created, suggesting an overachievement;
• Red shaded areas show the reverse, where the balance of chances was healthier than the actual goal difference, signalling underachievement.

Over the long term we’d expect the two lines to converge unless there’s a significant difference in a club’s attacking or defensive skill compared to the average for the division. We can’t tell from the data alone whether skill or luck is the cause, but the longer a difference persists the more I’d suspect the former.

Club-by-club graphics

Blackpool started brightly but it’s been pretty much downhill since then, with a less steep version of the same trend at Southend. Heading into the play-offs, Doncaster‘s performances are slumping at an inopportune time, while Sunderland – who I was initially suspicious of due to the extent they were overachieving by – have really pushed on in the last few months. Fleetwood will be interesting to watch next season as they also really stepped up in the latter half of the season.