This Week in Stats: Did the Premier League turn out as expected?

MANCHESTER, ENGLAND - MAY 06: Manchester City players celebrate with the Premier League trophy after the Premier League match between Manchester City and Huddersfield Town at Etihad Stadium on May 6, 2018 in Manchester, England. (Photo by Matt McNulty - Manchester City/Man City via Getty Images)
MANCHESTER, ENGLAND - MAY 06: Manchester City players celebrate with the Premier League trophy after the Premier League match between Manchester City and Huddersfield Town at Etihad Stadium on May 6, 2018 in Manchester, England. (Photo by Matt McNulty - Manchester City/Man City via Getty Images) /

How does the Premier League table compare to the expected goal stats? Were Manchester City worthy winners? Which three teams should’ve been relegated?

The 2017-18 Premier League season has drawn to a close. Manchester City were crowned champions, while Swansea, West Brom and Stoke were relegated to the Championship.

But did those teams, and the 16 others, deserve the season they had based on their underlying performance? Using the expected goal (‘xG’) data from FiveThirtyEight, This Week in Stats will attempt to answer this question.

The data from all 380 games this season has been compiled, and each match deemed to be a home win, away win or draw based on the xG difference. If a team amassed over 0.5 expected goals more than their opponents, then they “won” the fixture.

While that figure is arbitrary, it ensures the total points won by the league is within 22 of the expected total, so it seems a reasonable number to use.

The champions

Manchester City had a remarkable campaign. Pep Guardiola’s side set records for most goals, wins and points, and realistically had the title wrapped up months ago.

However, while they lost two matches, on the underlying stats they deserve to be unbeaten. Move over, Arsenal 2003-04, there should be a new invincible team in town.

City “only” merited 29 wins, but they should also have drawn the other nine matches. Even then, in only one of the draws were their shots worth less expected goals than their opponents’ were.

A round of applause, please, for Crystal Palace. They had a whopping 0.2 more expected goals than City at Selhurst Park, and then only thanks to an injury-time penalty. The champions are already odds-on to retain their Premier League crown, and on this form only a fool would bet against them.

The Champions League qualifiers

As for the rest of the top four, Tottenham and Liverpool deserve to be there, but the fourth team will surprise you: Arsenal. Wenger in, anyone? Despite only amassing four league wins on the road all season, the Gunners should by rights have picked up seven.

But it’s not so much their underachieving that has kept them outside the Champions League places, it’s the 18 unmerited points which Manchester United gathered.

Perhaps the term “unmerited” is harsh; with an excellent goalkeeper and decent strikers you can go a long way. However, while they’ve scored seven more than their attacking xG implies, they (or more accurately, the peerless David de Gea) kept out 18 goals more than they should have.

This has contributed to them picking up 10 away wins when they’ve deserved four. Funnily enough their biggest smash-and-grab took place at Arsenal; the Gunners’ shots in that match were worth 5.4 expected goals, which is the largest tally in any match in 2017-18, but United won 3-1. How different the prospects of Mourinho and Wenger would look now if decisions were based on underlying numbers.

The bottom three

The bottom two sides in the expected goals table are going down, so justice has been served. Swansea have been the worst side in the division on the underlying numbers, and Stoke have been little better. Both sides won more points in reality than they warranted, but not at the United-esque levels required to keep them up.

There’s one team though who stats would relegate but will be in the top flight next season, and it’s Huddersfield. They haven’t massively outperformed their numbers, they simply won three games more than the stats suggest they should have.

Timing can be everything though, and the Terriers won their first two Premier League matches when they didn’t deserve three points from either. Without those six points, they wouldn’t have had a solid foundation from which to build.

What of West Brom, the other relegated side? After all, they started 2017-18 with two wins too, but didn’t win any of the next 20. Unfortunately for the Baggies, they’re the only team in the bottom nine in the expected table who took fewer points than their performances merited.

What will surprise West Brom fans is the idea that Darren Moore has been lucky whereas Alan Pardew was not. The Baggies took just eight points under the latter, when the underlying performances suggested they should’ve had 24. As for Moore, his over-performance has been powered by undeserved 1-0 wins over United, Newcastle and Spurs.

So if justice had been served, West Brom would’ve stayed up and Pardew would still be in charge. Damned lies, Baggies fans?

Next: Goodbye Stoke, it's been... something

Any other business?

We can’t let this round up pass without making mention of Crystal Palace and Burnley, and here’s why.

Roy Hodgson deserves a lot of credit for steering Palace to safety, but in reality they could’ve done even better. Frank de Boer was fired after four defeats without scoring, yet on the numbers the Eagles should’ve taken five points from those matches.

His last match was against Burnley, when Palace lost despite posting 2.0 expected goals to the Clarets’ 0.3. Poor old Frank. As the table in the tweet shows, he wasn’t the only manager perhaps unfairly undone by Sean Dyche this season.

The victory over Palace was one of eight at Turf Moor which Burnley deserved to lose in 2017/18, yet they took 13 points from those matches. Congratulations to the Clarets for securing European soccer for the first time since the 1960s, but they can expect a drop off next year.

If they want a warning from history, they need to look to Newcastle in 2011-12. The Magpies finished fifth despite only having the 16th best expected goals difference that season. Where did they finish the following year? Sixteenth.

The Premier League table will never entirely match the underlying stats, but it can give pointers on what to expect in the future. Research suggests next season’s table will be closer to the expected goals chart rather than this season’s final standings. Bring on 2018-19, so we can all find out if that’s true here.