Championship trends, 20 Nov 2019
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.
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:
- The blue line shows the rolling average of a club’s goal difference over the last 10 league games;
- 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.
Bristol City, Nottingham Forest and Swansea all started the season far better than the balance of chances in their matches suggested they should have (denoted by the amount of blue on their chart) and currently Forest are the only one of the three whose results haven’t fallen back in step with the underlying data. On the flipside, both Stoke and Millwall looked far better than their league position and their recently-departed managers can feel a bit hard done by. Leeds also have a frustrating amount of red in their chart over the last few years.