Speaking of misleading health information, Barbara Delinsky has a gem in her book Sweet Salt Air. A woman in the story asks an overworked man, “When do you sleep?”

“When I’m tired,” he replies.

“Studies show that the less sleep you get, the greater your chance of stroke,” she warns.

“Studies get it backward,” he counters. “Insomnia is caused by stress, which causes high blood pressure, which causes stroke. I’m not stressed.”

This is another example of health information that “everyone knows,” but it’s not completely accurate. Even though a large percentage of people who have strokes might also have insomnia, the relationship between the two conditions is a correlation, not a cause-and-effect finding. The same is true of the studies that report people with more education have more migraine headaches. Education does not cause migraines, but it can provide a pathway to more stressful jobs, and stress causes migraines.

One of my great and useful take-aways from grad school was learning to be aware of the difference between correlation and cause-and-effect. All that tuition money wasn’t wasted.