Below is a guest post written by Paula Teander (@Sober_Sociology) from Wake Technical Community College.

“Why do you think the number of women having babies outside of marriage has increased?” I asked my Sociology of Family class. Knowing that students often blame pesky teenagers for these increases, I set the trap and waited for the first one to take the bait. The students were surprised that only 7.7% of out-of wedlock births (in 2008) occurred to girls under age 18. Then I brought up that non-marital births were actually higher in Scandinavian countries. “Is that because they’re all cold countries?” asked a particularly adept student. “What an excellent observation,” I said seeing a golden opportunity to point out the difference between correlation and causation.

In my excitement to draw the connection to causation I quickly said, “Did you know that ice cream sales and the incidents of rape are positively correlated.” A stunned silence came over the class; I thought they were mesmerized by my counter-intuitive gem. I went on, “It’s true, as ice cream sales go up more people are raped.” I went up to the whiteboard and drew out the relationship on a xy graph. I spent the next few minutes describing what a spurious correlation was, and how in this particular example it was the heat of summer affecting the increase in both.