Ladders, Cats, and Ice Cream

You can’t prove walking under a ladder won’t sometimes cause bad luck. No hard evidence rules out the chance that seeing a black cat brings misfortune. Scientists ignore reported cases of accidents during the week after such events. Enough people attribute unexpected trouble to walking under ladders or seeing black cats, it’s surely worth more study. Right?

Science hasn’t proved vaccines don’t cause autism, nor could it. You can’t prove a negative. A new web page by the Centers for Disease Control and Prevention is correct in saying that “studies have not ruled out the possibility that infant vaccines cause autism.” It’s not clear whether the CDC plans to keep studying vaccines and autism forever if no relationship is found.

Ice cream may be dangerous, too. During the polio epidemics of the 1940s, people noticed that outbreaks coincided with increased consumption of ice cream. Some public health campaigns recommended cutting ice cream from children’s diets to slow the spread of polio. Correlation does not imply causation. Both polio and ice cream cone sales peaked in the heat of summer. Both vaccinations and early signs of autism are concentrated in the first few years of childhood.

As CDC focus shifts from evidence to political messaging, many scientists on its staff face a tough choice: to resign or to adapt? Neither option will help make America healthy again.

​Images (left to right): Photos by Nick Page, Gio Bartlett, and Ian Dooley on Unsplash.