Doping pops up in the news

Thanks to the Olympics, doping has once again popped up in the news.

Some American athletes (and journalists) harshly criticized WADA (link), the international anti-doping authority, accusing it of covering up about 20 positive drug tests of swimmers from China who were subsequently exonerated and continue to compete; the Chinese investigators submitted evidence that these athletes unknowingly ingested the banned substances at a hotel. These accusations were flying around for months prior to the Paris Olympics, and created a situation in which any Chinese medalist in swimming would be viewed suspiciously, regardless of whether the athlete failed a drug test during these Olympics.

To someone who's not familiar with the landscape or history of doping in sports, the facts looked damning. But if you know anything about this subject, or have read Chapter 4 of Numbers Rule Your World (link), you should know better. The WADA process as described by these complainers is exactly how it has always been handled, even when the accused are U.S. athletes.

The vast majority of athletes who have tested positive for performance enhancing drugs have denied doping, and used a variety of excuses to explain away the test findings. There are even official "therapeutic use exceptions" (link) that permit athletes to use banned drugs if they suffer from some conditions. TUEs should be controversial. It has been previously noted that many swimmers have been granted exceptions due to asthma, making them much, much more likely than the general population to suffer from the condition.

Eventually, the Chinese authorities struck back, pointing to the case of an American track athlete who, you guessed it, failed a drug test, and was allowed to continue to compete after the American investigators submitted evidence that he ingested the substance unknowingly from contaminated meat (link).

This post was prompted by long-time reader Antonio R. who sent me an article about Jannik Sinner, the current world No. 1 tennis player from Italy, who has recently failed drug tests, and, you guessed it, was allowed to continue to compete after the Italian investigators accepted evidence that suggested that the banned substance could have entered his body through a spray used by his physiotherapist (link).

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As outside observers, it's impossible for us to judge who's lying and who's not. In my book, I made some observations about the anti-doping program:

1. It is far more likely that dopers are getting away with false negatives than innocent athletes who are wrongfully flagged with false positives. (Hence, the reference to "timid testers" in the title of Chapter 4.)
   
   
   
2. To come up with your own judgment of the effectiveness of antidoping, you can start by guessing what percentage of Olympics athletes might be doping. Is it 30%, 10%, 1%? Then, all you need to do is to look up what percent of tests have come back positive. When I did this exercise, the proportion of positives is way below the proportion of athletes who could be doping, which tells you that most of the dopers have been tested and tested negative.
   
   
3. The book was published before the fall of famous American cyclist Lance Armstrong, who, prior to admitting guilt, had always insisted that the hundreds of negative test results during his career represented a mountain of evidence that he was not a doper.
   
   
4. We should distinguish between a "chemical positive" and a "real positive". The chemical positive reveals that a banned substance was found to exceed the allowable level in the test. Crucially, the test finding itself cannot prove that the accused athlete doped, even if we want to believe it. Such a conclusion would require the assumption that the only way by which such substance could have entered the athlete's sample is via intentional doping.
   
   The history of athletes submitting alternative explanations for their positive tests is really very long. It ranges from the relatively boring such as eating contaminated meats to the extremely creative such as "the vanishing twin" (link).
   
   To nail down a "real positive," investigators have to locate actual evidence of doping, such as drug supplies or paraphernalia. Needless to say, it's very hard to prove such a thing. Armstrong was ultimately brought down by one of his former lieutenants.
   
   
   
5. It is equally hard for the accused athlete to prove that s/he has eaten a contaminated piece of meat. At best, they could show that meat purchased from some vendor contains the forbidden substance. But that tested meat isn't the meat that was eaten.
   
   It appears that the anti-doping agencies are quite willing to accept these explanations, and whether it's China, US, or Italy, they have been exonerating positive results based on these theories. Note that these athletes have not proven that the chemical positive was a false positive; by their response, they concede that the test was indeed positive, they just argue that it's not a "real positive".

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This topic fascinates me as it relates to statistical thinking. There are the measures (via tests) used as indicators of hypothesized causes. Then there is the causal gap, because the indicators themselves don't prove a cause.

For further thoughts on this topic, see Chapter 4 of Numbers Rule Your World (link).