More on the Age of Gymnasts: A Reply to Chris Bourdon
By ET
Photo of Yang Yilin, One of the Gold Medal Winning Gymnast
After I wrote a post and complained about Levitt’s un-scientific way of making ungrounded statements, I received a comment from the original data analyst Chris Bourdon. To make the reply more visible, I put it here, and it gives a little bit more about how I look at this issue.
Chris, thanks very much for the comment. The original purpose of writing that blog post was to show my disappointment with Prof. L. From your original analysis and your comment, I can say you are very scientific and possess the quality of an inquisitive thinker.
I did not spend too much time writing down my thoughts on this in the original post, here I’d like to add my two cents to the discussion.
There are two types of explanations on why gymnasts are smaller (in terms of size, not age) than their peers.
1. when young girls practice gymnastics, their bodies receive a trigger to stop growing (this may well be caused by injuries, etc.)
2. smaller girls enjoy an advantage in performing better.
Both explanations introduce some possible reasons that cannot be directly observed and verified in the Chris Bourdon analysis.
Explanation 1 may tell us that maybe due to the poor training conditions, etc. Chinese girls suffer more injuries than their US counterparts, and therefore look smaller. Or, maybe some special technique they use gives the necessary trigger to stop their growth. Of course, simply by comparing the girls with the national growth chart does not give us enough evidence to suggest that they are smaller than they should be. A better measure would be comparing these gymnasts with girls from other countries (Japan, Russia, etc.) and see if gymnast girls are also smaller in these other countries. Japan may give us a control for race (Asians), and Russia may give us a control for way of training (government supported intensive training).
Explanation 2 introduces an issue of self-selection. Those girls who are smaller enjoy a benefit, therefore, good gymnasts are smaller. If you do better (and in the case of Olympics, you do exceptional), you are, by-definition, not average. So compare these girls with the national chart is not the right way to control for this self-selection problem. I’m not sure about the gymnasts, but from what I hear on TV, I know that one of the Chinese gold medalist for diving did not eat dinner for 3 years. Her weight is only 28kg (61 lb). (Wang Xin: http://results.beijing2008.cn/WRM/ENG/BIO/Athlete/3/235963.shtml).
Also, think about SUMO wrestlers, if you do the same charting thing, they would appear awkwardly large compared to the Japanese average. It is simply determined by the profession, and you just cannot compare these athletes with the national chart to make any meaning inference.
Overall, I agree with you on that there should be no limitations on the age. But as there is such a de facto limit, out of academic prudence, I would hesitate to point fingers at these small girls before I have good evidence to suggest that they mis-report their ages.
