Not long ago I thought I had discovered the worst misinterpretation of a study on Covid vaccines, but I have just encountered another contender for the title. It was a study about vaccination and traffic crashes.

The authors explain that “[They] tested whether COVID vaccination was associated with the risks of a traffic crash,” and they concluded that “COVID vaccine hesitancy is associated with significant increased risks of a traffic crash.”

They meant much more than “associated.” They meant that vaccine hesitancy increases the risk of a traffic crash, a causal claim, just like the claim that Covid vaccines reduce the risk of death.

How do I know that that was their claim? They remarked that the study was not a randomized trial, and they used statistical methods to support inference on cause-and-effect relationship from an observational study.