Championship trends, 12 Nov 2018

We’re far enough into the season that it’s worth updating the long-term trend graphics, which show how a club’s results and underlying performances compare over a three-season period. These are explained in full here and briefly below.

Explanation

These are adapted from a very similar design by the Swedish blogger Zorba138 and are intended to track a club’s long-term performance, plus 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

Garry Monk certainly has Birmingham pointed the right way, with Frank Lampard having restored Derby’s fortunes with impressive swiftness. Hull looked to be on the up over the course of last season, but that momentum hasn’t carried into this campaign at all. At Ipswich, Mick McCarthy was one of the game’s masters when it came to keeping the chart blue, but that knack has departed with him. Nearby, Norwich have suddenly found another gear after a disappointing start, which is perhaps an understatement as they now top the division. Sheffield Wednesday’s bright start wasn’t reflected in the underlying numbers so it’s not surprising to see that fizzle out unfortunately. I’m a bit worried about Wigan, who started brightly but have seen both performances and results tank lately.