Estimation of injury costs: financial damage of English Premier League teams’ underachievement due to injuries

Introduction

Decision-makers in both the private (eg, stakeholders, CEOs, managers) and public (eg, officials in the Ministry of Health, Social Security analysts) sectors are interested in the overall financial loss caused by injuries, and also in the potential cost savings resulting from injury prevention.1 Financial loss is an outcome measure that enables quick comparisons among different types of injuries across a variety of industries. In this regard, the industry of professional sports requires its employees to perform at high intensities and at the highest limit of their physical capacity. As a consequence, professional athletes often suffer from injuries of various types and diverse severity.2

Football (soccer) is a team contact sport which requires intense physical demands (high speed running, jumping, tackling, changing directions), and as such its players are prone to both contact (eg, concussion) and non-contact (eg, hamstring strain) injuries.3 4 The assessment of the overall effect of a single player’s absence caused by injury in team sports is not an obvious pursuit, however, in recent years, attempts have been made to examine this issue. The most straightforward approach for assessment of the financial burden of injuries is to record time-loss injuries and to count the total number of days lost due to these injuries. The literature commonly defines time-loss injury as any physical complaint which was sustained during a competitive match or in training that resulted in a player being unable to take part in, at a minimum, the player’s next practice or official match.4

For example, Mosler et al5 reported that a professional football club can expect 6.6 groin injuries per season, resulting in a total of 85 days lost. Roe et al,6 in a longitudinal study of hamstring injury rates, found that Gaelic teams typically sustained 9.0 hamstring injuries per season, resulting in 299 time-loss days.

A more comprehensive approach would be to account not only for time loss by injured players but also for team performance, as reflected by accumulated wins and by annual ranking. Applying this approach, Hägglund et al7 showed that lower injury incidence and higher match availability were associated with higher final league ranking and with increased points per match in European football. Similar findings were reported by Williams et al,8 who recorded all time-loss injuries incurred by English Premiership rugby players during seven consecutive seasons.

A number of researchers went beyond the assessment of time loss and wins ‘left on the table’ due to injuries, and were able to assess the financial impact of injuries on the organisation. Hickey et al9 reported on the significant increase of financial costs due to hamstring strains, after combining the athletes’ annual salary for the 2003–2012 seasons with publicly available information on injuries in the Australian Football League (not the common association football also known as soccer). Donaldson et al10 performed a retrospective analysis of publicly available media sources to collect injury and salary data and to assess the amount of salary paid by clubs to injured players.

Similar cost analyses have also been published by various media outlets for the English Premier League (EPL) teams. For example, according to the 2016–2017 seasonal injury report published by ‘Physioroom’ (https://www.physioroom.com/), Premier League clubs suffered an average of 1410 days lost (SD=554) and 58 injuries (SD=16). Combining days out due to injury with the injured players’ annual salaries enabled the analysts to measure the teams’ injury-related wage bill. As reported by ‘Physioroom’, the total EPL injury-related wage bill for the 2016–2017 season was £181 million, meaning an average of £9 million per team in one season.

In the current article, we attempt to go one step further—beyond the existing measurements of the salary paid to injured players. Our aim is to estimate the effect of injuries on the performance of teams in the EPL, and to account for detrimental influences of injuries on the teams’ income. The EPL is one of the most popular football leagues globally. Live matches are aired in more than 212 countries and territories, reaching approximately 4.7 billion viewers.11 The EPL restricts access to the television (TV) market by not allowing broadcasters to negotiate with individual clubs, and instead forcing them to buy a package from the central negotiating body. To estimate the financial impact of injuries on team performance in the EPL, we used a prize money breakdown by season-end ranking (TV rights included), alongside deficits in prize money between the bottom three places in the Premier League and the top three places in the English Football League (EFL) Championship (one tier lower), as an assessment of the financial impact that relegation has on a club. Furthermore, we also considered the prize money for achievements in European competitions.

Methods

Results

Examples of the impact of injuries on team performance based on the difference between expected and actual season-end rank are presented in table 1.

The data presented in table 1 serve as an example for the analysis performed for each season in order to determine the difference between a team’s expected and actual seasonal outcome. We proceed to assess the explanatory power of days lost due to injuries on the difference between a team's expected and actual finishing rank.

In figure 1, a statistically significant relationship (r=−0.46, 95% CI −0.6 to −0.28, p<0.0001) can be seen between the number of days out due to injury that a team suffers per season and the place difference between its expected and actual rank. Using a linear regression model, we can interpolate that approximately 271 days out due to injury may cost a team one place in the table. Taking into account, for example, that in the 2016–2017 season Premier League clubs suffered an average of 1410 days out due to injury, and given the statistical model described above which translates to 271 days out to a loss of one league place, we can estimate that a Premier League club drops an average of six places in the table, in comparison to their expected finish according to the squad’s worth. This six-place drop translates to an estimated average of £36 million.

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A similar procedure was applied to assess the explanatory power of days lost due to injuries on the difference between the expected number of annual points based on the team squad’s worth and the actual number of points collected.

Figure 2 displays the statistically significant relationship (r=−0.38, 95% CI −0.54 to −0.2, p=0.001) between the amount of days out due to injuries a team suffers during a season, and the point difference between their actual and expected (according to the overall players’ worth) finishing place in the EPL. Based on the linear regression model, we can interpolate that approximately 136 days lost due to injury causes a team the loss of one league point.

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Discussion and conclusion

In line with the existing literature, the current analysis suggests that player injuries impose a major impact on team performance. This impact can also generate substantial financial damages, some of which we tried to estimate in our current investigation. Based on the relationships we found in our study between injuries and a team’s performance, we estimate that an average EPL team lost approximately £45 million per season due to injury-related decrements in performance. This estimation is based on the assessment of the team’s underachievement due to injured players (£36 million) and on a direct calculation of salaries paid to injured players (£9 million). Losses associated with transfer fees and a drop in the players’ worth due to injuries were not taken into account in the current study, but are expected to be substantial as well. Therefore, professional football clubs are increasingly investing in injury-prevention programmes and enhanced return-to-play protocols.12

The club’s investment in injury prevention and rehabilitation is reflected by the establishment of extensive sports science departments, and the hiring of scientific experts in various domains, such as physiology, biomechanics, sport medicine and nutrition. Hence, alongside a growing investment in technology that monitors various aspects of player performance and well-being (eg, Global Positioning System (GPS) tracking, camera-based tracking, biomechanical screening, isokinetic testing), analytical tools are being used to enable the gathering of insights from the collected data.

However, as illustrated by the data presented in our study, the current methods used in professional football seem to be insufficient when attempting to reduce injury rates and magnitude. As can be observed from our data, the increased volume of injuries in the EPL was a visible trend throughout the period examined in the current study. However, formidable scientific teams are at work on the clubs’ behalf to reduce injury rates.13 Although football clubs have been spending substantial portions of their budget on technology aimed at improving injury prevention and return-to-play protocols, it seems that there are still missing links in the effort to better mitigate this problem.

There are various possible assumptions as to what these missing links might be. One could consist of additional data sources that are not currently being collected which are highly correlated with injury occurrence and risk, or perhaps there is a need for improvement in the measurement accuracy of the current technology. Additionally, due to the multifactorial nature of injuries in professional football, a missing link might be the need to use powerful analytical tools, such as machine learning and artificial intelligence, which are frequently used in other industries but as of yet not in professional sport performance (eg, in basketball or football).

Limitations

Our calculations in this study can be used to form an interesting estimation of the impact that injuries may have on a team's performance and the financial effect this impact may imply. However, the correlation coefficients found in the current study showed that days out due to injury accounted for 21% of the variance in place in the EPL table, and for 14% of the variance in points achieved. This is to say that the remaining portion of variance was associated with other factors.