We can divide everyone into two types of people — those of us who have diabetes or those who don’t. Or we can divide us into men and women. Or into people who can read and write compared with those who can’t.
“Wait a minute!” you might exclaim. “That’s already a lot more than two types.”
Precisely. And that’s just the problem with all those studies that purport to show that two situations that occur today have a cause-and-effect relationship.
A greater proportion of people in those countries with a high rate of literacy have diabetes than in those countries where people are less educated. That’s a correlation between diabetes and literacy. It doesn’t prove that education causes diabetes.
Maybe the rate of diabetes has gone up in this country because more people live in homes that have air conditioning. Those two variables do correlate. But that doesn’t prove that one caused the other.
We have so many types of people in fact that each of us is unique. And no study can possibly control for every type of difference among us.
Yet scientific researchers continually bring forth new studies correlating one sort of change with another. These studies do have a real value.