I had a patient once who had just been diagnosed with mitral valve prolapse and was very worried about it. Mitral valve prolapse is a minor condition in most cases. The mitral valve in the heart bends inward when it closes instead of straight across. A significant percentage of the population has mitral valve prolapse without any symptoms, in fact, without even knowing that they have the condition. This young woman had read somewhere that it was possible to die suddenly as a complication of mitral valve prolapse.
“You know,” I said to her, “it just happens I looked that up yesterday. The risk of sudden death is almost exactly one in a million.”
“Isn’t that awful,” she said.
This woman did not understand what one in a million means. In fact, it is not so easy to understand what one in a million means. I had the same problem, myself. I was once told by a doctor that something I was worrying about was very unlikely, “about one in a million”; and that did not stop me from worrying either. This is what happened:
At the age of 14, my son, Mickey, was admitted to a hospital with an acute case of ulcerative colitis. Because he had lost a considerable amount of blood, he was given two transfusions. He recovered and was discharged. But a few months later the first cases of AIDS were reported in the medical literature; and it was not long after that that it was recognized that the disease was caused by a virus. The blood supply was known to be contaminated. At that point, and for years afterwards, there was no test for the virus, so I had no way of knowing whether or not Mickey had contracted the disease.
When I asked the head of the New York Blood Bank what the chances were of Mickey’s having received a contaminated pint of blood, he said “about one in a million.” I did not feel reassured for two reasons: it sounded like “one in a million” was a figure of speech, meaning very unlikely. I really wanted to know the exact odds. Secondly, he didn’t really know. It was too soon to know—really know. In the next number of months, I did my own calculations, based on new information that was becoming available. I thought the odds were worse than that, about one in 200,000. I knew this meant that his chance of developing AIDS was really very low; but I worried still every time he got a cold or some other infectious disease. After a while, new reports suggested that the odds were even worse, maybe one in 100,000, I worried more. Then, finally, I figured the worst possible case. The source of blood in New York was more contaminated than elsewhere. He had two transfusions, which doubled the risk, and so on. The very worst odds I could figure suggested that he had a one in two hundred chance of having caught the virus—and at that point I stopped worrying! This was so paradoxical and so striking, it took me a while to figure out what had happened. The fact was, I realized, that one in 200,000 was just a number to me. But I understood on a gut level what one in two hundred meant. I could visualize a statistic like that. And the number seemed really small.
I run a special program for people who are “health worriers,” that is, people who worry all the time about being sick, usually with some hidden, but fatal illness. Consequently, I spend a lot of time trying to get them to understand the real risk of a particular illness. If they discover that the risk of, let’s say, leukemia at their age is one in 15,000, they are not reassured. They cannot visualize a number like that. In general, they are not very good with statistics, anyway. I had a patient who knew that the life-long risk of breast cancer in women was one in eight. What she really wanted to know, of course, was her risk of developing cancer—in the next ten years, at her particular age. When I asked her what she thought the risk was, she said, “One in four.” How could the risk of developing cancer between the ages of 40 and 50 be one in four if they are only one in eight over the course of a lifetime? And, of course, there are those who say firmly that with their luck, no matter the odds, they will be the one stricken. They say this usually with a smile. But these individuals, also, can be reassured if they really come to understand the odds.
Women who are pregnant have a series of tests to determine the likelihood that the child they are bearing will have Down’s syndrome. One laboratory reports the results in a very clever way. They cover a page with 100 small line drawings of a baby. If the odds of giving birth to a Down’s child are one in a hundred, one of the babies is colored red. At a glance, the pregnant woman gets a feel for the chances of this mishap.
So, if a patient is worried about a disease that has a one in a ten thousand chance of striking her, I ask her to cover a very large piece of paper with this mark: IIII with a / across it. (This represents the number five. You have seen this figure in movies where prisoners are keeping track of the days they have been in jail.) She has to make these marks until they total a thousand. (This takes some time) I ask her, then, to paste this large piece of paper on a wall; and then paste nine other large pieces of paper next to it. Then, she has to color one of the marks red. This works. Now she knows what one in ten thousand means.
It turned out Mickey did not develop AIDS. Instead, he picked up another virus, Hepatitis C, through those transfusions. Hepatitis C is an important illness which has infected millions of Americans without their knowing it. It produces no symptoms, for decades. It is, however, the commonest reason for a liver transplant. It can cause cirrhosis, or liver cancer. It was untreatable at the time Mickey contracted the disease, but there was no test for it then, either. By the time I found out he had the illness, about 20 years later, a treatment had been developed. He is now virus-free, although there is still about a one in 200 chance that it will return. I am not worried, though. (c) Fredric Neuman 2012
Follow Dr. Neuman's blog on his web site fredricneumanmd.com/blog