Part 2: Using Expected Points & Goal Difference to predict a league table
Updated: Jan 9, 2019
In my previous post on Expected Points I discussed the differing metrics I can use in roughly trying to predict the outcome of a league season in the format of a final league table. Due to the length of part one on the EPL I decided it would be easier to do a second post rather than bore everyone to tears on the first post but thanks for a massive response all the same! For the explanations of the parameters and metrics used in compiling these tables I suggest you refer back to the first post which can be found here https://wp.me/p8dqLB-8l
EFL Championship and SkyBet Leagues 1 and 2
Having been involved in differing capacities with clubs below the EPL, alongside supporting the best team in the midlands, Aston Villa (don’t @ me!), I have not only a vested interest in the Championship and League’s 1 and 2 (I will leave the National League out of these posts for now for post length reasons) but I also compile and collect these 3 league’s data throughout the season and find that they are very interesting when it comes to using various measures when producing data work.
Although there is some work published I believe that there is nowhere near enough detailed data and stat work around given the availability of various data sources however publicly available data is few and far between in all fairness. These three leagues are all well supported of course and fans maybe don’t get enough stat work done, or publicly published anyway, on their clubs but especially fans from clubs in Leagues 1 and 2. I should say that the data I used is up until and including the 6th of October’s fixtures in all three leagues.
More on Leagues 1 and 2 later but I will start with the Championship and alongside the tables I will sum up little about what I found and then see what possibilities could end up taking place come the end of the season.
EFL Championship
As I mentioned in the first post on this subject I had my doubts about using expected goal difference as a valid measure of a team’s final league position but in the process of exploring the data and using the metrics went along it kind of grew on me a little.
Will Dean Smith's departure for Aston Villa radically effect Brentford's promotion hopes?
Brentford fans will be pleased as punch to see their side at the top of the goal difference table but they might want to hold off due to the fact manager Dean Smith has now left the club to join Aston Villa and this of course will most probably have a huge impact on where their season goes from here. A +22 goal difference would have earned you a final league position of 5th or 6th position if we go, as we have done in our parameter, by last season’s final league table. Wolves won the league with a +43 GD with the nearest being another promoted club Cardiff City with +30 GD and of course it’s still possible to achieve Cardiff’s GD but unlikely anyone will touch Wolves’ 17/18 season total surely.
My doubts creep back in again when I see the high pressing Marco Bielsa’s Leeds team finishing the season with a GD of +14 when they already have a +13 GD at the time of writing but there is a long way to go of course and goal differences will sway, some considerably, as the season progresses. Sheffield United have started very well but xG doesn’t always match up with the reality but in theory a playoff spot, if not more, is easily attainable for Chris Wilder’s men.
Sheffield Wednesday bottom of a table? I have my doubts.
So who should be worried? Well Hull and Ipswich (yes really) could be in trouble as most certainly will relegation favourites Rotherham United but the surprise (okay MASSIVE surprise!) is seeing Sheffield Wednesday at the bottom of this table. This is just not going to happen Wednesday are currently 6th in the table with a GD of +1 so how is it feasible they could finish bottom? They have conceded 15 goals with an xGA of 18.1 (9th highest in the Championship) so still conceding 3.1 less than predicted, a small margin granted. And they are exceeding there xG by 4.3 goals (xG is 11.7 and actual goals scored is 15) again this isn’t a great number but it is still 8th highest in the league, not bad (I am planning on publishing all leagues current xG numbers when I get a chance). The issue is essentially conceding 18 goals and scoring 19 isn’t sustainable over a 46 game season and if this continues they will find themselves slipping down the table somewhat however not to the extent that the table above shows. Wigan, Bristol City, Stoke, Villa in 12th, 13th, 14th and 15th respectively all have similar records so the although the final table is skewed somewhat it’s easy to see how, given the four teams positions noted above, Wednesday could end up much lower down the league come May next year.
Anyway let’s move on to the final expected points table to see if we can correlate anything the goal difference table tells us.
EFL Championship expected points table
Now this is more like it. For me this passes the eye test quite well. The top 6 sits quite well with me and the fight for the title, I expect, will be just as close as the table suggests although Sheffield United winning the title may be a stretch for me.
Some numbers suggest otherwise but I think Sheffield United should be taken seriously this season.
Brentford as we have discussed may have issues now Smith has departed. In general the top five are the same give or take (yes I know there are is no such thing as 77.04 points but you can see what we are trying to achieve here) 7th-18th is again very familiar and also the bottom 4. Sheffield Wednesday have managed to get out of the bottom four and finish 20th, probably more believable but I still have my doubts they will finish that low we shall see.
Summary
The two tables do correlate in general but with complications for teams in regards to managerial changes, injuries and schedules etc there can always be a massive swing either way on how things can change especially with two or three big wins changing goal differences up and down the table. I like the expected points tables in general and although being massively swayed by the teams xG numbers these are consistently more reliable than using current points per game. I would expect Leeds and Middlesborough to better their positions in my table but I’m interested to see how Brentford, Sheffield United and Derby progress and also how the Dean Smith effect at Aston Villa pans out.
SkyBet League 1
SkyBet League 1 goal difference and expected points tables
Four out of the last five seasons have seen the League 1 title won by a team with a points total of 90 or more and Barnsley look on course, even at this early stage, to achieve this, well maybe. Barnsley earned another 3 points against Luton on Saturday.
With the lowest xGA conceded (12.5 actual conceded is 9) and the highest xG at 23.1 (they exceed this by 2.9 with 26 goals scored) and scoring at 2.1 goals per game the numbers are looking really good for the Oakwell outfit so far who are in 3rd. Portsmouth and Peterborough lead the way currently and both of those sides are looking good and with the latter’s expected goal difference of -5 in my final table this again questions my thinking but 19 goals conceded with an xGA of 21.2 kind of skews the table given that Posh have currently scored 30 goals and exceed their xG by a whopping 8.8 this then answers the question of my table somewhat in terms of goal differences but again slightly questions the sustainability of Steve Evans’ teams goal scoring and goal conceding ratios over the course of a season.
Luton Town are another side that has real potential in at least achieving a playoff spot. In their first season back in League 1 and in both the goal difference tables and the expected points table the Hatters are predicted to end up in the higher echelons. With a predicted GD of +17 (last season this would get you 4th-5th position and the predicted 77 points would get you the same position wise) Nathan Jones has a real team spirit and huge work ethic ingrained into his side which I believe will all help in them in achieving a somewhat surprising top 5 finish.
Sunderland, Southend and a resurgent Blackpool all look to have decent chances of a playoff berth each come the end of the season. At the other end of the table Plymouth, who finished 7th last season but currently sit bottom of the table this season, already look worryingly frail at the back with a rather large 2.18 xGA per match (actually conceding 1.83) and with a huge total xGA of 26.3 after 12 games played they have been very lucky to concede just the 19 goals maybe they have a kind of alright defensive policy after all? Or does it say more about the shooting ability of the teams they have faced? You can decide (Hint: it’s not the first one) anyway it doesn’t make for optimistic reading and I predict them to finish bottom, and some way short of 23rd, in both of my predictive tables.
These results and metrics used are probably shoved to the back of any clubs data driven stat work at this level of football and is probably paid no attention to at all when in reality this could be massively important and relevant in a clubs performance now and in a predictive nature.
SkyBet League 2
SkyBet League 2 goal difference and expected points tables
So to the last league being covered in this article SkyBet League 2 and one of the most competitive with a standard being very similar throughout the league. There are some interesting outcomes here but let’s start at the top as it stands.
One thing is for sure so far this season. The Cowley brothers and Lincoln City side have found their promotion winning form when winning the National League two years ago. Finishing 7th last season, The Imps already have just over half the points they achieved in the whole of last season. With an xG total of 14.3 this season Lincoln have scored 20 goals at the time of writing (games inc. 6th of October remember) a plus of 5.7 xG means they sit pretty at the top of League 2 and also predicted to keep that top spot come the end of the season with a points total of 83.68 (or 84 if you like your numbers rounded up) a points total that last year would have got your team a 4th place finish stretching to 3rd (Wycombe finished in 4th with 84 points last season).
I can’t quite get my head around a +18 GD when winning a title in this league but this is what MK Dons are predicted to achieve in my goal difference table and its odd I agree especially given Lincoln already have +17 currently but in achieving fourth last season Wycombe did finish with the same goal difference so again although doubt creeps in it is still feasible, maybe. Speaking of MK Dons I have them coming very close in the expected points table with a predicted total of 78 points which last season would see you end up in either 5th or 4th position so comparing my table with last season’s it won’t be far off.
Looking up and down there isn’t much that sticks out between the two tables in terms of positioning and GD is pretty good as well with Grimsby predicting to have a -18 GD (23rd and 24th ended with -13 and -15 respectively last season) and could Mansfield end up with the same amount of points as last year (72) as predicted in my table? Can Notts County recover from a disastrous start to the season and end up escaping to 20th position with 51 points by the end of the season? in any instance it is more likely than them achieving 77 points as they did last year.
In the last two seasons 46 points or above would see you safe from relegation but using my measures 50-52 will be the probable cut off this year and the likes of Macclesfield (currently on 4 points), Cambridge (8), Cheltenham (9) and the aforementioned Notts County (12) will not be wanting to hear that I’m sure.
So there we have it I hope I have cleared up a few things and maybe reaffirmed some peoples thinking and hopes for the season ahead or maybe I have opened a few eyes to what is possible when using these metrics alongside the parameters I have used when compiling these tables.
Probably worth putting a few quid on anyway, maybe.
Gareth Cooper
G.C Analytics
If there are any queries or questions in regards to the past two articles on this subject or others involving xG, xA or any predictive measures you have seen and if you think they may help when scouting teams or players or even if you think I could help your club or department in any of these areas feel free to get in touch.
First published in October 2018.