# DEFF: Relationship Between Goals Conceded and Points Dropped

1 Apr

I initially introduced the concept f measuring a teams true defensive efficiency (DEFF) in previous posts based upon several stats such as SoTC and SoTC/GC. This post looks at the relationship between Goals Concede (GC) and the number of points a team drops per season as opposed to wins.  Why look at this you may ask? Well as we know the team who drops the least amount of points wins the league and generally teams that have the worst goal difference get relegated (see Omar Chaudhuri’s excellent 5 added minutes blog for more on that).  However as seen in my last post the teams at the top and bottom of the goal difference table don’t necessarily follow the same pattern GCs.

Aim

With this in mind I wanted to see if there was a relationship between the number of goals conceded vs the number of points lost during a season and league position.

Method

Using data from www.statto.com for the 2010/11, 2011/12 and 2012/13 season I collected the number of goals each team conceded (GC) and calculated the number of points dropped (PD) by teams (points won – total points available).  I then divided PD by GC to calculate the average number of points dropped per goal conceded.

Results

The graph below shows the league position vs. average points dropped per goal conceded (PD/GC) (the variables).  The green line indicates the teams that finished in Champions League positions, the orange line shows the teams qualifying for the Europa League, the gray lines shows the half way point and the red line shows the teams in the relegation zone.  The legend on the graph show the different league seasons and the black line of bets fit indicates the basic pattern or distribution of the variables.

As can be seen the is a very clear bell shaped curve with the teams finishing in the top 4 and bottom 3 having, on average, the lowest PD/GC with teams finishing in the mid table table cluster of 8-14th having the highest.

In order to finish in the top 4 it would generally appear that a team needs to have PD/GC -0.2 below the league average PD/GC.  Therefore as shown previously a team finishing higher up the league can afford to concede a relatively higher number of goals per game over the season due to their higher ability to score more goals.  Conversely teams who are in the relegation should maybe not head quite as much on the side of caution as was previously thought.  While keeping a tight defense is an important quality and one which is constantly pointed to by the pundits, the data indicates that a team should look to risk conceding more goals in exchange for increasing their chances of scoring more.

Southampton are an excellent example of this. In the past 6 games they have the a record of W3 D1 and L2 with a goal difference of 11-9.  This is a PD/GC differential of 0.78 which is top 2 form.   So while Southampton have conceded 1.5 goals per game they have committed to being brave and attacking their way up the table.

Conclusion

The aim of the post was to see if there was a relationship between league position goals conceded and points lost.  The initial data shows that that the top teams have the lowest as would be expected however more interesting is the relationship between PD/GC and finishing in the relegation zone and mid table.

If anyone would like to look at the data I’ve pulled together or look at collaborating on future work please feel free to get in touch.