With the Dutch Eredivisie taking its usual winter break, the opportunity arises to apply some of the most promising metrics in football analysis to other leagues around Europe. The driving force behind this initiative, as is true for most of the work on this site, is curiosity. In this case, it is curiosity to compare the Eredivisie to other leagues in terms of Relative Shot Rates (RSR) and PDO. But before we come to such comparisons, let’s study the findings in other leagues, starting with the most prominent league in the world, the English Premier League.
For those unaware of the terms RSR and PDO, let’s start with the latter for a short summary. A more extensive description can be found in the post on separating luck and skill, which introduced the concept of PDO on this site. The term PDO is adapted from ice hockey analysis, where it was introduced by Brian King (whose internet alias happened to be ‘PDO’) and picked up by James Grayson, who first applied it to football and has taken it further from there.
PDO is the sum of a team’s saves percentage and shot percentage, where saves percentage is the fraction of conceded shots that don’t result in a goal, and shot percentage is the fraction of shots created that results in a goal scored. For convenience, PDO is multiplied by 1000 to get rid of the decimals.
The RSR is an extension to the TSR, which stands for Total Shot Rate. A team’s TSR is computed as the fraction of shots created from the total number of shots in all matches played by the team. The RSR is a slight adaptation, which compares a team’s number of shots created and conceded with the league average against the same opposition. More details on the method behind TSR and RSR are found here.
Without further ado, here’s the EPL league table, updated with Match Day 22 results, including RSR and PDO. Remember, a high RSR signifies a relatively high ratio of shots created, and is a strong characteristic of sustainable good performance. A high PDO signifies a high ratio of shots converted and/or saved, which has proven to be a lot less sustainable over the longer term.
In general, high PDO teams are found in the top half of the table, and low PDO teams in the bottom half. The team with the highest PDO (1062) is Manchester United, mostly due to their immense conversion rate of 17.4%, which is over 50% better than the league average of 11.1%. The other exceptionally high PDO is Chelsea, but also Stoke, West Ham and Swansea punch above their weight, with PDO’s at a level that could only be sustainable by top teams. From a recent long term PDO analysis, we’ve learned that PDO’s outside of the 980-1020 zone seem unsustainable beyond the scope of a single season, while inherent differences in team quality may account for variations within this zone. So, we may expect Manchester United, Chelsea and to a lesser extent Stoke, West Ham and Swansea to drop off a bit in the remaining part of the season.
Remarkably low PDO teams are clustered near the bottom, where all of Newcastle, Aston Villa, Southampton, Wigan and QPR look set for an improvement on their points-per-game haul so far. Also, Liverpool and Tottenham rank low in terms of PDO, which means an improvement in terms of points-per-game is just around the corner.
In terms of RSR, there is quite a clear top-3, with Manchester City, Liverpool and Tottenham the only teams above the 0.600 mark. This means that, with hypothetical equal conversion rates, these three teams would be in a close fight for the title. And, since shot rates are a lot more sustainable on the long term than conversion rates and saves rates, these three teams reflect the best underlying performance level. Behind them, Everton and Arsenal are a close 4th and 5th, with Chelsea at 6th place. Perhaps remarkably, league leaders Manchester United come in just 7th in terms of RSR. This indicates that Sir Alex Ferguson’s team is highly reliant on substantially higher conversion and/or saves rates, which seems a precarious base for future success. However, so far, their exceptional PDO has earned them a gracious seven point lead over rivals Manchester City, which may well be enough to win the league.
Based on these parameters, the top-3 will most likely be United, City and Tottenham, with a close battle for fourth between Chelsea, Everton, Arsenal and Liverpool.
A the bottom of the table, both RSR and PDO spell doom for recently promoted Reading. They are the bottom team in terms of RSR, and by a distance, but their PDO of 1017 indicates that their shots and/or saves percentage has been above the average EPL level, which is more than can realistically be expected of this side. A PDO at the low side of the 980-1020 zone seems more realistic and a disconnection with the pack battling for survival seems imminent for Reading.