In Simon Rolfes, the Bundesliga and its partner AWS have an expert who knows the Bundesliga from A to Z. Bayer 04 Leverkusen's Sporting Director, Rolfes wore Die Werkself's colours 288 times between 2005 and 2015, and represented Germany on 26 occasions. Rolfes is the ideal man to write a weekly column for the 'Bundesliga Match Facts Zone' on bundesliga.com, analysing current trends and giving unique insight on the Bundesliga Match Facts.

This time, he discusses the Bundesliga clubs' xGoals values, and their relation to the actual number of goals they have scored.

By Simon Rolfes

For a considerable time now, there has been quite a discussion in football, and the Bundesliga is no exception, regarding xGoals. Yet these highly interesting real-time statistics, which have been part of the Bundesliga Match Facts since the end of last season, must be considered in the correct context: xGoals alone does not say a great deal.

>>> xGoals and Goal Probability explained

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After 16 matchdays, with the first half of the Bundesliga season almost played, I would like to take a look at all of the clubs' xGoals values compared to the actual number of goals they have scored. Just as a reminder, xGoals refers to the number of goals a club would have been expected to score in view of chances they had created. When a team has scored far more goals than its xGoals (xG), this means they have been particularly efficient with their chances, whereas when a team has scored fewer goals than their xG value, they clearly need to sharpen their clinical edge in front of goal.

Bayern, Leverkusen and Union with the greatest efficiency

The by far most efficient team in the Bundesliga so far this season is FC Bayern München. The league leaders would have been expected to have scored 31.87 goals in view of their xG, yet Hansi Flick's men have plundered a total of 48 already. No other club in the Bundesliga comes even close to such a positive difference between actual goals and xG! Bayer 04 Leverkusen are second in this particular classification with 29 goals scored from an xG of 21.18, with one of the league's surprise packages Union Berlin just behind them with 6.6 goals in excess of xG. This goes some way to explaining why they are enjoying such a good season, with a high level of efficiency in front of goal. These three teams have so far succeeded in converting a good proportion of the chances they have been creating, which can only vouch for the quality they have shown.

Give Union Berlin an inch and they take a mile - Urs Fischer's men have been particularly efficient in front of goal this season. - Matthias Koch via www.imago-images.de/imago images/Matthias Koch

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Efficiency is not the only factor behind success, however. If you are only creating a small number of chances, having an above-average conversion only helps to a certain extent. I therefore believe it's always important to have as high an xGoals value as possible, since this means that the team is at least creating plenty of opportunities to score.

Stuttgart almost level with Bayern for xGoals

It may not come as a total surprise to see Bayern mingling at the top of these rankings with 31.87 xG – only Borussia Dortmund boast a higher value of 33.48. Yet whereas Bayern have been rather ruthless with their chances, Dortmund's efficiency pales in comparison to their rivals from Munich. For example, in their 1-1 draw with 1. FSV Mainz 05 on Matchday 16, Edin Terzic's men scored just once, in spite of an xG of 3.05, with Marco Reus' missed penalty obviously contributing to this quite considerably. VfB Stuttgart also boast an impressive xG of 31.82 this season – the third highest behind Dortmund and Bayern, which is recognition in itself of the refreshing attacking brand of football they have played. In terms of the goals they have actually scored (and own goals are not considered in this equation), Pellegrino Matarazzo's Swabians also boast an impressive level of efficiency.

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xGoals: Mainz have hope in the battle against the drop

To see the teams with the lowest xGoals values, such as DSC Arminia Bielefeld, FC Schalke 04 and1. FC Köln, all languishing at the bottom of the table is quite logical – especially since their xG is being combined with a low level of efficiency. The biggest hope among the teams struggling at the bottom of the table, then, belongs to 1. FSV Mainz 05. Bo Svensson's team ranks proudly in mid-table with an xG of 21.78, but with the unenviable statistic of being the team with the worst return on xG (15 goals). In other words, if Mainz were to become more clinical with their chances in front of goal during the second half of the season, they currently boast the best chances of staying up, among the relegation candidates.

About the clubs

Borussia Dortmund

SIGNAL IDUNA PARK

FC Bayern München

Allianz Arena

1. FSV Mainz 05

MEWA ARENA

1. FC Union Berlin

An der Alten Försterei

VfB Stuttgart

MHPArena