I’ve shown on numerous occasions previously that, at the team level in the Premiership, sh%, sv%, and PDO are more driven by luck than by talent.
For a sample size of >150 data points, sh% was found to be 39% due to talent and 61% due to luck, sv% was found to be 31% due to talent and 69% due to luck, and PDO was found to be 38% due to talent and 62% due to luck. Furthermore, this post gives a visual illustration of how each of these regress from extreme values over teh course of a season.
The sample size is larger now, standing at 204 back-to-back team seasons (where a team was in the Premiership for two straight seasons), so lets reproduce those original plots and see how they look. The average Premiership team takes 240 shots on target over the course of a season so in other words ~100,000 shots on target have been used in producing each of these plots.
Sh%
Sv%
PDO
So, the inreased sample size suggests that, at the team level in the Premiership, the variation from the mean of a teams sh% is 43% due to talent and 57% due to luck, it’s sv% is 38% due to talent and 62% luck, and it’s PDO is 44% due to talent and 56% due to luck. All of these are slight revisions upwards from the previous data, but also still make any of these metrics a pretty poor indicator as to a teams true talent.
To move quickly and go one step further, I’ve recently been using some penalty data provided to me by Infostrada (twitter, website), to look at whether removing penalties has an effect on the repeatability of sh%, sv%, or PDO. Those posts can be found here and here.
So if we remove penalties from sh%, sv%, and PDO, does their repeatability change? In this case the sample size is 170 back-to-back seasons between 2001-02 and 2011-12.
Sh%
Sv%
PDO
So, removing penalties lowers the correlation coefficient for both sh% and sv%, yet somehow leads to an increase for PDO.
Across the plots put up in both this post, and those linked at the top, the variation from the mean over the course of a Premiership season in terms of:
sh% is found to be 36-43% talent,
sv% has been found to be 31-38% talent, and
PDO has been found to be 38-46% talent.
In summary, luck dominates for each of these metrics at the team level over the course of a Premiership season.
James' Blog 