Who are the EPL's most injury-prone teams? And why?


So Arsene Wenger has finally decided that there is no room for Jack Wilshere in the Arsenal midfield this season and sent him off to Bournemouth on loan. Or maybe he just wanted to free up space in another Arsenal department: their treatment room. With Wilshere having missed more games than he has played in the last few years, Arsenal’s over-burdened medical staff probably feel like they are due a break. 

Many Arsenal fans that feel that their team have suffered more than their fair share of injuries, but is it really just a few unlucky seasons – and a few particularly fragile players – that stick in the mind? Or is it true that some EPL teams are really more injury prone than others? And if so, why?

The Treatment Table


To investigate this I looked at the total number of injuries suffered by EPL teams each year since the 2004/5 season (taken from here), providing me with 12 years of data encompassing 37 teams. In this dataset, an injury is defined as any condition that put a player out of action for at least two weeks, so minor niggles are not counted.[1]

Table 1 shows a list of these teams, ordered by the average number of injuries they suffered over the twelve-year period. To cut it down, I’ve only included teams that played in the EPL in at least three of the twelve seasons (if you’re curious, Leicester would be very near the bottom of the table, averaging 15 injuries per season in the two years since they were promoted).

Newcastle are the clear winners (or losers?), suffering a whopping 33 injuries per season. Man Utd bump Arsenal into third place, who – surprise, surprise – finish just above Spurs. Looking further down, it’s interesting how few injuries Chelsea players get – 19 per season, which is significantly below the EPL average of 23.

Table 1: Average number of injuries EPL teams have suffered in the twelve seasons since 2004/5.

Chronically Crocked


Of course, the number of injuries a team suffers varies from season to season. Arsenal, for example, went from 35 in the 2014/15 season to 24 last season. So did they just go through a particularly unlucky period, a few bad years, or are some EPL teams more injury prone than others?

To answer this, I broke my data set into two non-overlapping 6-year periods. The first period included the seasons from 2004/5 to 2009/10, the second from 2010/11 to 2015/16. I then calculated the average number of injuries suffered by each EPL team during each period. The results are shown in Figure 1.
Figure 1: Average number of injuries suffered by each EPL team during two six-year periods: the 2004/5-2009/10 seasons (x-axis) and the 2010/11-2015/16 seasons (y-axis). Only teams that played in the EPL in both periods are plotted.

The injury records of Arsenal, Manchester United, Newcastle and Spurs aren’t just bad, they’re consistently bad. Chelsea players, on the other hand, seem to be consistently good at avoiding injuries. In general, there is a clear correlation between the average number of injuries teams picked up in the two periods (the Pearson coefficient = 0.65, which is statistically significant).  Some teams are good at avoiding injuries, while others are particularly vulnerable.[2]

It’s difficult to find a clear explanation for this. Many of the EPL’s established teams are found near the top of Table 1 (with the notable exception of Chelsea), while the smaller teams seem to have a better injury record. You could argue that the better teams are more likely to receive injuries as they tend to control possession in matches and so opposing teams are forced to make more tackles. But then why are Newcastle, Portsmouth and Middleborough so high up? 

Alternatively, you could argue that the best teams play in Europe and get further in the cup competitions; they therefore play substantially more games. But again, why are Chelsea so low, and Newcastle – who have neither regularly played in Europe nor done well in the cups – so high? Squad size also doesn’t appear to be a factor.

However, squad age does seem to hold a clue to the puzzle. Arsenal have consistently had one of the youngest squads in the Premier League, with an average age of just over 24 over the last 12 years[3]. Spurs, Man Utd and Newcastle also tend to have young squads; all four teams have a history of promoting youth players to their first team. Generally, most big EPL teams have well-developed youth academies -- the average age of teams that have played in all twelve of the last 12 EPL seasons is 25. 

On the other hand, newly promoted clubs often try to consolidate their position in the highest echelon by recruiting experienced EPL players. Therefore, they tend to have older squads -- the average age of teams that have played less than six of the last twelve EPL seasons is over 26. 

The obvious implication is that older, more experienced players are better at avoiding injuries. However, there may also be a selection effect: if a young player can’t withstand the rigours of playing regularly in the EPL he won’t make it, no matter how talented he is. Only those that can withstand the constant battering will continue to play at the highest level.

Jack Wilshere may well be a case in point.



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[1] I prefer this measure to total number of days lost through injury – which physioroom.com also collect – as it isn’t dominated by a small number of serious injuries.
[2] The outlier to the right of the plot is Southampton. In 2004/05, the season in which they were relegated, they picked up 33 separate injuries. In the 4 years since their return to the EPL, they’ve substantially improved their injury record.
[3] Data taken from http://www.football-lineups.com/

Comments

  1. Interesting analyses - something in the water at Chelsea! Re smaller clubs recruiting older players, isn't there a selection bias or an automatic filter whereby injury prone players don't really make it

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