So, everyone agrees that Ole Solskjær has been a breath of fresh air at Man United and is largely responsible for their remarkable turn around this season. But here’s a great article by the guys at StatsBomb that adds perspective to that view. Sure, there’s been a change in results since Solskjær arrived, but more importantly xG – the expected goals – have also improved considerably, both in terms of attack and defence. This suggests that the results are not just due to luck; United are genuinely creating more chances are preventing those for the opposition at a greater rate than under Mourinho.
Nonetheless, United’s performance in terms of actual goals is out-performing that of xG: at the time of the StatsBomb report, total xG for United over all games under Solskjær was 17.72, whereas actual goals were 25; and total xG against United was 10.99, with actual goals at 8. In other words, they’ve scored more, and conceded fewer, goals than their performance merits. This suggests that, notwithstanding the improvement in performance, United have also benefited from an upsurge in luck, both in attack and defence.
But more generally, what is the value of a good manager? This recent article references a statistical analysis of data from the German Bundesliga, which aimed to quantify the potential effect a manager could have on a team. It’s not a completely straightforward issue, since the best managers tend to go to the best clubs, who are bound to have a built-in tendency for success that’s not attributable to the manager. Therefore, the research attempted to distinguish between team and manager effects. Their conclusions were:
- The best 20% of managers were worth around 0.3 points per game more than the weakest 20% of managers. This amounts to 10.2 points over a 34-game season in the Bundesliga.
- A manager’s estimated performance proved to be a valuable predictor in team performance when a manager changed clubs.
- The best and worst managers have a strong impact on team performance. For teams with managers having closer to average ability, team performance is more heavily impacted by other factors, such as player quality and recruitment strategy.
In summary, on the basis of this research, there is value in aiming for the best of managers, and avoiding the worst, but not much evidence to suggest it’s worth shopping around in the middle. There are some caveats to this analysis though, and in particular about the way it’s described in the Guardian article:
- The analysis uses data from German leagues only up to 2013-14.
- This amounts to a total of just 6,426 matches, and includes relatively few managers.
- The Guardian article states ‘budget per season’ was accounted for. It wasn’t.
- The Guardian article refers to ‘statistical wizardry’. This consists of simple linear regression on points per half season with separate effects for managers and teams. This might be a sensible strategy, but it’s not wizardry.
So, it’s best to treat the precise conclusions of this report with some caution. Nonetheless, the broad picture it paints is entirely plausible.
And going back to Solskjær: there are good reasons to believe he is partly responsible for the overall improvement in performance at United, but a comparison between goals and xG suggests that the team have also been a bit on the lucky side since his arrival, and that their results have flattered to deceive a little.