Stats & Links: Boateng + Thiago = success?

In comparison with other sports, particularly in the USA, football has developed relatively little in terms of statistics. In today’s stats & links article we take a look at the plus-minus rating and assess what conclusions can be drawn from the past season’s numbers.

Maurice

October 25, 2018

Plus-minus ratings from 2017/18

An initial step requires calculating the goal difference when a certain player was on the pitch. This value will be henceforth known as plus-minus.

**Overview of all plus-minus ratings of Bayern players for the 2017/18 season**
(Analytics: Lukas))

In the graph, the goal difference for all players in the 2017/18 season just gone is represented. Here the ratings are additionally plotted along the number of minutes played. A red line shows the team average, which was at 1.89 goals for the season. So Bayern scored precisely those 1.89 goals more per game on average than the opponent.

The different coloured areas correspond to the 90%, 95%, and 99% percentiles and can be understood as statistical quality criteria. Practically that means that the likelihood that Boateng only has such a good rating coincidentally is lower than ten percent, because his rating is within the 90% percentile.

The player-specific rating then still has to be offset against the team-average to get the actual influence. This value is designated henceforth as delta-plus-minus. In the table below, these ratings are now represented:

Name	Position	Minutes	Plus-Minus	Delta-Plus-Minus
Alaba	D	1556	2.37	0.48
Alcântara	MF	1245	2.1	0.21
Bernat	D	893	2.12	0.23
Boateng	D	1645	2.52	0.63
Coman	MF	1151	2.03	0.14
Hummels	D	2216	1.83	-0.06
Kimmich	D	2335	1.77	-0.12
Lewandowski	ST	2173	1.78	-0.11
Mai	D	180	3	1.11
Martínez	MF	1613	1.73	-0.16
Müller	MF	1965	2.11	0.22
Neuer	K	270	1.33	-0.56
Rafinha	D	1844	1.56	-0.33
Ribéry	MF	1210	1.56	-0.33
Robben	MF	1522	1.95	0.06
Rodríguez	MF	1626	1.66	-0.23
Rudy	MF	1513	1.73	-0.16
Starke	K	180	1	-0.89
Süle	D	1924	1.64	-0.25
Tolisso	MF	1532	1.53	-0.36
Ulreich	TW	2615	2	0.11
Vidal	MF	1460	1.79	-0.1
Wagner	ST	723	2.37	0.48

For a better overview, positive delta-plus-minus ratings are represented in green and negative ones in red. Here the data for the 2017/18 were evaluated. Like all statistics, the pure numbers still require an interpretation and classification.

Boateng and Alaba help the defence

If when evaluating you leave out the anomalies with few minutes like youngster Mai, returning Starke or long-injured Neuer, the ones who stand out are Alaba and Boateng. The two long-time key figures have with +0.63 and 0.48+ respectively absolute top ratings in the team. With the two on the pitch, Bayern score an average of half a goal more than without them.

With Boateng the precise analyse shows that he was only on the pitch for one defeat in the whole 2017/18 season – in the Champions League semi-final first leg against Real Madrid. And even in that game the German international left the pitch with an injury when it stood at 1-0 to Bayern.

Boateng showed as early as last season that he couldn’t reach his absolute top level anymore due to his injuries that constantly came back. But the Berlin-born defender seems to be an important anchor in Bayern’s defence.

A similar statement can be made for Alaba. The Austrian was also missing in a lot of games due to a range of injuries. His absences were insufficiently compensated for. In the eleven games that the former Bayern youth player missed, the side fell to three of their four defeats of the season.

In two of the three defeats, Alaba was covered for by Rafinha, which conversely explains the low rating of -0.33 for the Brazilian. The actual replacement Bernat comes in with a good rating with +0.23.

Thiago and Müller boost the midfield

With the midfielders, most of the players exhibit a negative plus-minus-delta. In terms of the positives, merely Thiago with +0.21 and Müller with +0.22 stick out. As a result, the Bayern veteran outstrips his direct “competitor” James by 0.45 net goals/game.

It’s particularly with James and Müller that further analysis would be interesting, one that demonstrates how the plus-minus changes when only one of the two are on the pitch or indeed both of them together.

While Thiago’s influence on Bayern’s game is sufficiently appreciated here on the blog as well, in light of his plus-minus the limits of how much can be read into the rating should be explained.

The Spaniard, with +0.21, has a strong plus-minus rating, especially in comparison with his team-mates in midfield like Martinez (-0.16) or Tolisso (-0.36). Here too an organised view of the games completed by the number six helps. In total Thiago missed 15 Bundesliga games. Of these, two were lost. The points average with and without the midfield director is exactly the same at 2.47 points/game.

So where does the good plus-minus rating come from for Thiago, who is better than his team-mates in comparison? With the Spaniard in the line-up, Bayern won six times by more than three goals, doing so not once without him.

The plus-minus rating, then, is suited to comparing various players and evaluating their performances. However, it should not be used without considering further statistics like points achieved per game, because otherwise individual conclusions can be weighted too heavily.