Guest post: Understanding risk

Originally a comment by Claire on Expertise.

Sigh. Why aren’t people taught risk better in school? I find that many people outside of STEM (and many within it too) just do not understand risk, nor do they understand the difference between the two models

If the probability that a woman is injured in a tackle from a transwoman is 20-30% (as per World Rugby) then the demoninator is the tackle. In Harper’s formulation, it’s more complicated but the answer may not be what she expects.

Let’s propose an imaginary trans woman who had been a short, weedy man and transition made him lose muscle and even bone density to that of a woman’s (unlikely but this is a thought experiment). He’s still going to represent a risk to the women on the field. Because men’s and women’s rugby is played differently. Female physiology means that the style of play involves fewer head-on tackles and shoulder tackles, and more tackles from the side. This actually increases the risk of concussion in women’s rugby.

Add our imaginary transwoman playing in a male style would be unpredictable to the women on the team because she would not attempt tackles (and other maneuvers) in the same way. And if she learns the style, she’s still a risk because biomechanical factors mean that women have a higher rotational speed of their head during a tackle. Rotational speed is very, very bad, as you might imagine. And all the hormones in the world won’t change that. Nice paper here.

So, yes, the number of transwomen on rugby teams is small right now. Currently the top 30 women in women’s rugby average tens to hundreds of tackles per match. Let’s look at Jess Breach at number 30 in the 2018 Sevens – she made only 60 tackles in that entire tournament. If our imaginary trans woman made a similar number of tackles and taking the low end 20% risk per tackle, that means as many as 12 injuries could result from that tournament. And that is assuming one transwoman in the entire tournament.

Those 12 are excess injuries, i.e. the number of additional injuries incurred by having one transwoman in a tournament who made 60 tackles. The number 1 player by tackles in 2018 was Portia Woodman, who made a whopping 215 tackles. You do the math.

So Harper can go take a long walk off a short pier. Claiming that the risk has to be calculated as a function of number of transwomen in a tournament or league is not helpful to her cause because it underlines the disruption just one transwoman makes to injuries resulting from that tournament.

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