Building on the data I’ve started collecting on DEFF I thought it prudent to ask the question do shots actually lead to goals? This question on the surface of it may seem mad however if we examine the stats there is method to the madness.
The first thing to accept is that shots are a rare occurrence in football when taken into account for a 90 minute game, with goals being an even rarer occurance, hence the soaring costs of strikers. Therefore do the number of shots a team concedes actually relate to the number of goals or is it luck/skill of the specific player taking it?
I have collected the number of total goals conceded (GC), total shots conceded (TSC) and the SC in the box (SCB) for each team playing in the EPL between the 2008/09 season and 2011/12 season (props to @dankennett for the data). This has provided a sample of 80 teams over 4 seasons and 1520 games, making the sample size reasonably robust in terms of carrying out statistical analysis.
From this data as with the previous posts I have used a simple correlation to determine the strength of relationship between the different variables.
Looking at the relationship between TSC and GC there is a moderately strong correlation (r2 = 0.51) which indicates that 51% of GC are as a result of the total number of shots conceded by a team. As you can see this is quite a strange finding which indicates that because a team concedes a large number of shots it doesn’t necessarily mean they will concede lots of goals.
Presumably however there will be a significantly stronger relationship between the number of shots conceded in the box and the number of GC as this is what we’re told by the experts? Well as you can see the r2 value has increased to 0.64 (rounded up) which shows that 64% of goals conceded are as a result of shots conceded from inside the box. The relationship is stronger but again you would assume it shots in this key area should account for closer 80%.
So what does this data tell. Firstly that conceding or having lots of shots does not mean your team will score/concede lots of goals. This leads to the several potential conclusions:
1. Luck plays a large part in goals being scored
2. The standard of shooting is extremely poor outside of goal scoring experts
3. Only a minority of players have the ability to convert chances
4. Defences are extremely efficient at preventing high quality goal scoring opportunities
5. Teams are extremely wasteful of opportunities or lack the patience to create a ‘genuine’ goal scoring opportunity.
The next step to add more clarity to this position will be to collect total shots on target data, who takes the shots and where are they taken from. This will then allow us to understand just how much of a waste a time shots actually are.