Championship trends, 2017/18

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


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

Barnsley‘s relegation was a strange one, as the balance of chances created and allowed makes them look like a solid mid-table side. However the results haven’t gone their way this season after a bright start evaporated.

Birmingham have been underachieving for a year and a half but look to have finally clicked under Garry Monk, so there’s plenty to be optimistic about next season even if results are still lagging behind their improved performances.

Bristol City‘s performances have nosedived since the turn of the year despite some improved results of late. Something needs to change over the summer if they’re to sustain a promotion push next term.

Derby are another side whose performances have tanked lately. The Rams were running incredibly hot during the middle of the season, but as the goals started to go against them they started to look a lot worse, so play-off success would be quite an achievement.

Mick McCarthy’s departure from Ipswich looks to have ended a sustained period of overachievement. Their graph has been blue for much of the last three seasons, suggesting that their former boss was doing something special that expected goals data doesn’t pick up – they’ll need to recruit carefully over the summer.

Reading also need to have a good summer: just like last season, a strong start has given way to a prolonged slump in performances, but this time there wasn’t a hot streak of results to mask the decline. Expect Paul Clement to ring the changes and look to impose his own approach, as he certainly has the mandate for radical action.