Lloyd Christmas: What do you think the chances are of a guy like you and a girl like me ending up together?
Mary Swanson: Not good.
Lloyd Christmas: You mean, not good like one out of a hundred?
Mary Swanson: I’d say more like one out of a million.
Lloyd Christmas: So you’re telling me there’s a chance….
—From Dumb and Dumber
My last column described the Identifiable Victim Effect and how people are heavily influenced by even a single anecdote. This human tendency to focus on a single anecdote can be especially problematic when doctors tell patients not to worry about rare, but severe, side effects of medication, for example, that only one patient in 1,000, or even one in 10,000, experience the rare event. Patients will focus on that one, not the 1,000 or 10,000. They will heavily overweight the probability of the rare event and may be too scared to take your otherwise wonderful medication.
A patient of mine who needed a potent medication for his severe skin disease best illustrates this problem. He would not consider taking the needed medication. He had in his mind that the medication might cause liver disease despite the lack of any real known risk of liver disease. I asked him if he would take the medication if there were only a one in 1,000 risk of liver disease. Slamming his hand down on a table, he stated vociferously, “No! You’re not listening to me! I would NOT take it. I had a relative who died of cirrhosis. It was a horrible death. I would not take the risk!” I said, “Okay,” and asked, “If I had another medication in which 99 out of 100 don’t get liver disease, would that be acceptable?” And he said, thoughtfully, “Yes, I would take that.”
What “Sounds” Safer?
What an odd, but typically human way to view numbers! A drug for which 99 out of 100 don’t have a problem is 10-fold more risky than a drug that has a one in 1,000 risk of a severe event. Yet the “99 out of 100 don’t have a problem” presentation sounds safer to the human brain than saying one in 1,000 do have a severe, bad outcome.
When presented with a one in anything chance, the human mind grabs onto that “one,” especially when it is something laden with emotion, such as a devastating side effect or the chance (however miniscule it is mathematically) of winning the billion dollar Powerball lottery. With the graphic mental picture of that event standing out in the mind, the risk (or benefit) seems totally out of proportion to reality—as when Jim Carrey asks Lauren Holly about the potential for getting together in the movie Dumb and Dumber dialogue presented at the top of this column.
People imagine what life would be like to win the lottery, or to have that truly horrible rare side effect. They frame a detailed mental picture of it; and it ends up seeming much, much more likely to happen than the true probability. Human brains just aren’t made for making good probability judgments, especially for rare events.
The solution to patients’ excessive fears of rare, but severe, adverse events is easy, if the compliance attorney will let you do it. Instead of telling patients (or doctors) there’s a one in 1,000 risk, let them know that 999 out of 1,000 don’t get the problem. The math is identical, but the effect on human perception is completely different.