Beware the Ice Cream!

Are these darling boys in imminent danger of drowning?  You might think so, if you don’t understand correlational coefficients, one of the cornerstone concepts of research, especially important in the behavioral sciences.  Beginning a lecture with “Today we are going to discuss correlational coefficients” is a guaranteed buzzkill.  So, present this scenario: “It has been shown that the number of drownings and the amount of ice cream consumed can be correlated.  Does this mean that if I eat ice cream, I am likely to drown?”

I see a lot of surprised and puzzled faces. I continue, “A correlational coefficient means that as one variable (ice cream eating) increases, the second variable (death by drowning) also increases. Why would this be?”  Typically, students are still mystified.  I turn to the board and write, “When do people consume the most ice cream?”  Students reply, “Summer.”  A few light bulbs begin to flicker.

Next question: “When do most people go swimming…including the ones who aren’t very good at it?”  Aha! (I love the ahhhhh moment, don’t you?) Finally, students realize that ice cream consumption and swimming are related by the time of year in which they occur.  The fact that they happen at the same time does not mean that one causes the other. Bingo!

Understanding the difference in correlation and causation is now an achievable challenge, and one that will have value for them as they continue to study not only psychology but other disciplines as well.  They are proud of owning some “special knowledge,” and are able to come up with their own examples, some of them quite funny.  Students regularly tell me that this is the most memorable concept in Introduction to Psychology.

In his bestseller Drop Dead Healthy, A.J. Jacobs mentions our confusion about causation and correlation: “To cite a famous example: Diabetes rates are much lower in areas where people own passports. Therefore, you might conclude that owning a passport prevents diabetes. Right? Wrong. It’s more likely that passport owners are wealthier, and wealthier people can afford healthier food.”

Do you have favorite strategies or examples for helping students understand the difference in causation and correlation?  We wish that you would share them here!

—Anne

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