Michael Phelps’ hickies

Ok, they’re not hickies, but NPR referred to them as such, so I’m going with it… I’m talking about the cupping marks.

The NPR story can be heard (or read) here. There were two points made in this story that I think would be useful and fun to discuss in a stats course.

The first is the placebo effect. Often times in intro stats courses the placebo effect is mentioned as something undesirable that must be controlled for. This is true, but in this case the “placebo effect from cupping could work to reduce pain with or without an underlying physical benefit”. While there isn’t sufficient scientific evidence for the positive physical effect of cupping, the placebo effect might be just enough to give the edge to an individual olympian to outperform others by a small margin.

This brings me to my second point, the individual effect on extreme cases vs. a statistically significant effect on a population parameter. I briefly did a search on Google scholar for studies on the effectiveness of cupping and most use t-tests or ANOVAs to evaluate the effect on some average pain / severity of symptom score. If we can assume no adverse effect from cupping, might it still make sense for an individual to give the treatment a try even if the treatment has not been shown to statistically significantly improve average pain? I think this would be an interesting, and timely, question to discuss in class when introducing a method like the t-test. Often in tests of significance on a mean the variance of a treatment effect is viewed as a nuisance factor that is only useful for figuring out the variability of the sampling distribution of the mean, but in this case the variance of the treatment effect on individuals might also be of interest.

While my brief search didn’t result in any datasets on cupping, the following articles contain some summary statistics or citations to studies that report such statistics that one could bring into the classroom:

PS: I wanted to include a picture of these cupping marks on Michael Phelps, but I couldn’t easily find an image that was free to use or share. You can see a picture here.

PPS: Holy small sample sizes in some of the studies I came across!