How a Serious Finger Infection Got Me Questioning the Difference Between Causation and Correlation

We often assume that “A” caused “B” when the linkage only coincides.

Photo of my finger that the author took.

I know it looks gnarly. I was filleting a grouper we caught about ten days ago and got a dorsal spine stuck into my finger. I washed it with fresh water, but it got infected. For those unfamiliar with the spines on a grouper (and why would you?), they are akin to metal bbq skewers, only sharper. This has happened to me before, but it has never got infected.

This infection is called paronychia. Since I am immunosuppressed and on a biologic for my Crohn’s disease, my risk of infection is higher than normal. It could be a coincidence that I have just started a new medication (Skyrizi). One of the side effects of the drug is an increased risk of infections. Or it could be unrelated. Which one is true is anyone’s guess. In my case, it doesn’t affect how I treat it. Warm vinegar soaks, antibiotics, and, if no better, surgery to release the pus under the nail.

Since the pandemic, many writings have been about the difference between correlation and causation. The distinction is important but often takes more work to discern. Knowing the difference is the cornerstone of science, statistics, and medicine and has led to countless arguments about treating Covid-19…