The other day I watched CBS News medical contributor Dr. Celine Gounder report new findings that drinking caffeinated coffee reduces the likelihood of dementia. She warned that this may be due to correlation, not causation—creating puzzled looks from the hosts. Then Dr. Gounder explained that individuals in poor physical and mental health will often be put on a diet that restricts caffeine. Aha!
It never ceases to amaze me how often people fall for correlation being causation. Here are some of my favorite examples:
- As I reported in a blog a few days before Christmas of 2012,* partygoers took advantage of a buy-one-get-one-free (BOGO) sale on a fine wine—paying $17 for one bottle and a nickel ($0.05) for the other. They drank the first bottle and thus worried greatly if it would be OK to bring the cheap wine to the party.
- Per Google’s AI, the most popular example of correlation versus causation is that ice cream sales and shark attacks both increase during the summer months. While they correlate, eating ice cream does not cause shark attacks; rather, a third variable—hotter weather—causes both, leading people to eat more ice cream and swim. Banning ice cream (addressing the correlation) would not reduce shark attacks (the causation), highlighting the mistake of assuming one directly causes the other.
- Most popular with statistics teachers—Umbrellas and wet streets both increase on rainy days, but umbrellas do not cause the streets to get wet.
- Being called in to troubleshoot processes at our manufacturing sites the operators explained to me that performance varied due to the phase of the moon.
“Cars with flames painted on the hood might get more speeding tickets. Are the flames making the car go fast? No. Certain things just go together. And when they do, they are correlated. It is the darling of all human errors to assume, without proper testing, that one is the cause of the other.”
― Barbara Kingsolver, Flight Behavior
But don’t become too skeptical about seemingly spurious connections between cause and effect, such as me questioning my daughter’s assertion that the color of otherwise identical flying disks affect their performance.
*Correlation of price of wine with the fineness of its taste–an absurd example