On 2015 Jan 20, E DAVID KLONSKY commented:

MMA Fighters Experience Less Head Trauma Compared to Hockey and Football: A Re-Analysis of Data in Hutchison et al. (2014)

E. David Klonsky PhD, Department of Psychology, University of British Columbia

Hutchison et al. (2014) present the most detailed and authoritative analysis to date of head trauma in mixed martial arts (MMA) competitions. The study is a valuable contribution to the literature on the frequency and predictors of head trauma in combat sports. This comment was written to suggest a reinterpretation of a particular aspect of the paper.

Hutchison et al. estimate the number of concussions that occur per 100 ‘athlete exposures’ in MMA, and compare their finding to data from other sports, including hockey and football. The figures reported are: 15.9 per 100 exposures for MMA, 8.8 for football, and 2.2 for hockey. Reported this way, the numbers imply that participating in MMA results in significantly more head trauma than hockey or football.

However, the authors’ choice to standardize concussion figures per 100 athlete exposures overlooks a key consideration: it is not only the rate per exposure that matters, but the sheer number of exposures. It is significant, then, that the number of exposures per year and per career varies systematically across sports.

Consider that a National Hockey League (NHL) regular season consists of 82 games, and that a National Football League (NFL) regular season consists of 16 games. In contrast, MMA fighters average approximately 3 fights per year. If we adjust the Hutchison et al. figures for number of exposures per year, concussion rates become highest for hockey and lowest for MMA: 1.80 for hockey, 1.41 for football, and 0.48 for MMA. In other words, a typical year of competition in professional football or hockey results in 3 to 4 times more concussions than a typical year of competition in MMA.

It is also important to consider head trauma experienced over the course of a career. To do so we must first consider the number of career exposures typical for each sport. As a rough barometer of career exposures, let us consider players recently inducted into each sport’s Hall of Fame. The four 2014 NHL player inductees competed in an average of 1201 career games. The seven 2014 NFL player inductees competed in an average of 206 career games. In contrast, the last four fighters to be inducted into the UFC Hall of Fame competed in an average of 33 career matches.

Notice the massive discrepancy in average career exposures across sports: 1201 (hockey) vs. 206 (football) vs. 33 (MMA).

If we use these differences in career exposures to adjust the concussion figures reported by Hutchison et al., we get the following: 26.4 for hockey, 18.1 for football, and 5.25 for MMA. In short, the concussion rate for an MMA career is 3 to 5 times lower than that of a hockey or football career.

This analysis, like the Hutchison et al. analysis, has limitations. First, the Hutchison et al. figures for MMA concussions were based on official bout results and video analysis rather than medical diagnosis. Second, the figures for hockey and football cited by Hutchison et al. were taken from previous studies using different methodologies and sampling procedures. Third, my analysis focuses on professional sports, which have longer seasons (i.e., more exposures) than sports at collegiate, high-school, or recreational levels. Fourth, I roughly rather than precisely estimated the average numbers of career exposures. Finally, a full understanding of head trauma risk in sports requires data on concussions that occur during practice and training, not just competition.

In sum, understanding the risks of head trauma in sports is critical. Some have been quick to associate MMA with disproportionately high risk of head trauma compared to other sports. However, when the stakes are high, it is important to get the science right. And the available data suggest that professional MMA fighters will experience less, not more, head trauma compared to professionals competing in hockey and football.

On 2015 Jan 20, E DAVID KLONSKY commented:

MMA Fighters Experience Less Head Trauma Compared to Hockey and Football: A Re-Analysis of Data in Hutchison et al. (2014)

E. David Klonsky PhD, Department of Psychology, University of British Columbia

Hutchison et al. (2014) present the most detailed and authoritative analysis to date of head trauma in mixed martial arts (MMA) competitions. The study is a valuable contribution to the literature on the frequency and predictors of head trauma in combat sports. This comment was written to suggest a reinterpretation of a particular aspect of the paper.

Hutchison et al. estimate the number of concussions that occur per 100 ‘athlete exposures’ in MMA, and compare their finding to data from other sports, including hockey and football. The figures reported are: 15.9 per 100 exposures for MMA, 8.8 for football, and 2.2 for hockey. Reported this way, the numbers imply that participating in MMA results in significantly more head trauma than hockey or football.

However, the authors’ choice to standardize concussion figures per 100 athlete exposures overlooks a key consideration: it is not only the rate per exposure that matters, but the sheer number of exposures. It is significant, then, that the number of exposures per year and per career varies systematically across sports.

Consider that a National Hockey League (NHL) regular season consists of 82 games, and that a National Football League (NFL) regular season consists of 16 games. In contrast, MMA fighters average approximately 3 fights per year. If we adjust the Hutchison et al. figures for number of exposures per year, concussion rates become highest for hockey and lowest for MMA: 1.80 for hockey, 1.41 for football, and 0.48 for MMA. In other words, a typical year of competition in professional football or hockey results in 3 to 4 times more concussions than a typical year of competition in MMA.

It is also important to consider head trauma experienced over the course of a career. To do so we must first consider the number of career exposures typical for each sport. As a rough barometer of career exposures, let us consider players recently inducted into each sport’s Hall of Fame. The four 2014 NHL player inductees competed in an average of 1201 career games. The seven 2014 NFL player inductees competed in an average of 206 career games. In contrast, the last four fighters to be inducted into the UFC Hall of Fame competed in an average of 33 career matches.

Notice the massive discrepancy in average career exposures across sports: 1201 (hockey) vs. 206 (football) vs. 33 (MMA).

If we use these differences in career exposures to adjust the concussion figures reported by Hutchison et al., we get the following: 26.4 for hockey, 18.1 for football, and 5.25 for MMA. In short, the concussion rate for an MMA career is 3 to 5 times lower than that of a hockey or football career.

This analysis, like the Hutchison et al. analysis, has limitations. First, the Hutchison et al. figures for MMA concussions were based on official bout results and video analysis rather than medical diagnosis. Second, the figures for hockey and football cited by Hutchison et al. were taken from previous studies using different methodologies and sampling procedures. Third, my analysis focuses on professional sports, which have longer seasons (i.e., more exposures) than sports at collegiate, high-school, or recreational levels. Fourth, I roughly rather than precisely estimated the average numbers of career exposures. Finally, a full understanding of head trauma risk in sports requires data on concussions that occur during practice and training, not just competition.

In sum, understanding the risks of head trauma in sports is critical. Some have been quick to associate MMA with disproportionately high risk of head trauma compared to other sports. However, when the stakes are high, it is important to get the science right. And the available data suggest that professional MMA fighters will experience less, not more, head trauma compared to professionals competing in hockey and football.