As we’re a decent way into the new season, I thought that it was worth updating the long-term trend graphics to see how each club has fared in recent seasons. These are explained in full here and briefly below and this year I’ve expanded the data range from three seasons to five to get a fuller picture of how each club’s performances have evolved.

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

You’ll notice that there isn’t a blue line for seasons where a club were in the National League – this is due to the lack of publicly-available shot data for that division. I’ve also got barely any data for Salford as they were in the National League North the season before last and I don’t have any data for that division at all. Forest Green have a lot of blue on their chart this season, suggesting that their promotion challenge may not be sustainable – however their performances are starting to improve dramatically. Both Scunthorpe and Walsall have had disappointing starts to the season that weren’t reflected in the underlying data, so it was no surprise to see the Iron’s fortunes improve and the Saddlers’ should too.