2013/14 PL: 8 Game Splits & Repeatability

Banksy

I'm going to post a few tables on how teams have fared in their first 8 games and the the most recent 8 games. 8 game splits, if you like. Points, Goal Difference, shots information and scoring/save percentages.

Am I the only who thinks that looking at each teams performance over the first 8 games and the next spell of 8 games is actually pretty cool? Just me then.

8 game splits is a tiny sample to work with, so any information is merely helpful rather than definitive. Hell, even 19 game splits would be an insufficient sample to work with.

What will follow is a collection of stat tables and the repeatability of each stat from the first 8 games of the season to the second 8 games of the season. Each group of 8 games is separate and none of the information overlaps. I must also state that this article is merely foreplay to a main event which will look at which stats are the best predictors of future goal difference or points totals.

It's all well and good knowing which stats are repeatable, but what we really really want to know are which stats are predictive of future outcomes in terms of the aforementioned goal difference and points. But that's for next time.

OK, we'll start.

Points

Points Games 1-8 Games 9-16
Arsenal 19 16
Aston Villa 10 9
Cardiff 8 9
Chelsea 17 16
Palace 3 10
Everton 13 16
Fulham 10 3
Hull 11 8
Liverpool 17 16
Man City 16 16
Man United 11 14
Newcastle 11 16
Norwich 8 11
Southampton 16 9
Stoke 8 10
Sunderland 2 6
Swansea 10 10
Tottenham 16 11
West Brom 10 5
West Ham 9 6

Southampton, West Brom and Fulham were the teams who dropped off to the largest degree in the first  8 games v the next 8 games. Palace improve.

Splits_points_medium

Pretty meh relationship between the two sets of results. I'd include goal difference at this juncture but the results are too similar.

Shots +/-

Shots +/- Weeks 1-8 Weeks 9-16
Arsenal 18 7
Aston Villa -6 -14
Cardiff -59 -54
Chelsea 65 39
Palace -28 0
Everton 26 28
Fulham -86 -63
Hull -44 1
Liverpool -2 69
Man City 56 67
Man United 15 -3
Newcastle 26 10
Norwich -40 -34
Southampton 19 29
Stoke -9 -38
Sunderland -10 -65
Swansea 16 -1
Tottenham 67 38
West Brom -10 2
West Ham -14 -18

Palace improved, Liverpool blew the doors off. Tottenham, Chelsea and Man United regressed. Quality of opposition may well be a big factor here.

Splits_shots_medium

R2 of 0.55 isn't too bad at all.

Shots On Target +/-

SoT +/- Weeks 1-8 Weeks 9-16
Arsenal 16 10
Aston Villa -5 -5
Cardiff -32 -14
Chelsea 24 16
Palace -20 4
Everton 19 13
Fulham -20 -23
Hull -14 -9
Liverpool 7 27
Man City 28 25
Man United 10 -1
Newcastle 3 5
Norwich -17 -20
Southampton 12 9
Stoke -9 -15
Sunderland -23 -7
Swansea 16 3
Tottenham 22 3
West Brom -6 -12
West Ham -11 -9

Huh, Cardiff, Palace and Sunderland all improved in the second chunk of 8 games.

Tottenham, Swansea and Man United regressed.

Splits_sot_medium

Slight improvement on the predictability when using shots on target instead of shots. Still early in the season, though.

Scoring%

Scoring=goals for/shots on target for

SC% Weeks 1-8 Weeks 9-16
Arsenal 33.96 42.86
Aston Villa 33.33 25.93
Cardiff 42.11 18.18
Chelsea 29.17 46.15
Palace 27.27 20.00
Everton 26.67 35.90
Fulham 34.62 24.00
Hull 31.82 33.33
Liverpool 27.66 52.00
Man City 38.46 60.00
Man United 25.58 44.83
Newcastle 27.50 29.41
Norwich 24.00 31.03
Southampton 21.05 36.36
Stoke 13.79 45.83
Sunderland 26.32 38.89
Swansea 25.53 33.33
Tottenham 16.67 15.56
West Brom 28.00 34.48
West Ham 38.10 17.24

Scoring% is pretty much all over the place. Here's how the first bucket of scoring% predicts the second bucket of scoring%:

Splits_save__medium

A correlation of 0.01 between two sets of variables is really poor. Essentially there is no relationship.

Save%

Save= 100-(goals against/shots on target against)

SV% Weeks 1-8 Weeks 9-16
Arsenal 75.68 66.67
Aston Villa 68.75 66.67
Cardiff 74.51 75.68
Chelsea 79.17 48.00
Palace 59.52 63.16
Everton 61.54 83.33
Fulham 78.26 54.55
Hull 75.00 65.52
Liverpool 82.50 66.67
Man City 62.50 57.14
Man United 69.70 68.97
Newcastle 62.16 74.19
Norwich 69.05 68.00
Southampton 88.46 45.45
Stoke 81.58 67.57
Sunderland 52.38 65.52
Swansea 64.52 61.54
Tottenham 80.77 50.00
West Brom 80.65 60.00
West Ham 75.00 67.65

Again, this is pretty much all over the place.

Splits_save__real_medium

A negative slope to this chart. A negative correlation is probably best explained like this:

The more time I spend at the mall, the less money I have. The more time I spend at the office, the more I question the purpose of existence.

The higher a team save% was in the first 8 games the lower it is likely to be in the next 8 games. But that effect isn't huge, the correlation is just r2=0.22.

Save% and Scoring% numbers in the first 8 games were shitty predictors of Save% and Scoring% in the next 8 games. What happens if we put both of these stats together and call it PDO?

PDO

PDO Games 1-8 Games 9-15
Arsenal 109.6 109.5
Aston Villa 102.1 92.6
Cardiff 116.6 93.9
Chelsea 108.3 94.2
Palace 86.8 83.2
Everton 88.2 119.2
Fulham 112.9 78.5
Hull 106.8 98.9
Liverpool 110.2 118.7
Man City 101.0 117.1
Man United 95.3 113.8
Newcastle 89.7 103.6
Norwich 93.0 99.0
Southampton 109.5 81.8
Stoke 95.4 113.4
Sunderland 78.7 104.4
Swansea 90.0 94.9
Tottenham 97.4 65.6
West Brom 108.6 94.5
West Ham 113.1 84.9

In most cases PDO shows little or no relationship from the first group of 8 games to the next group of 8 games.. The chart points this out:

Splits_pdo_medium

A very slight negative correlation. But it's a wash really. Many people will point to our advanced understanding of shots location and their importance in separating teams from their basic numbers. Maybe they have a point, but the early season splits, and the r2 valuations in scoring%, save% point to those stats having very little repeatability league wide.

I think Mike Goodman put it best:

*****

Putting all this information together we end up with a table like this:

R2
Sot For 0.68
SoT +/- 0.59
Goals For 0.56
Shots +/- 0.55
Shots Against 0.53
SoT For % 0.42
Shots for 0.37
Points 0.35
Goal Difference 0.31
SoT Against 0.21
Goals Against 0.13
Scoring% 0.01
SoT Rating% -0.001
PDO -0.05
SoT Prevention% -0.14
Save% -0.22

I could have included around 15 or 20 other stat categories, but I think we've all seen enough for now.

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