How well do we understand and act on probabilities that something will happen? A 30 percent chance of this or an 80 percent chance of that?
As it turns out, making decisions based on the odds can be an extremely difficult thing to do, even for people who study the science of how we make decisions.
Brian Zikmund-Fisher would know. He teaches about risk and probability at the University of Michigan School of Public Health. Back in 1998, when he was studying behavioral decision theory in graduate school, he was diagnosed with myelodysplastic syndrome. People with the disorder can't produce blood cells the way they should, making them much more susceptible to bleeding and infection.
Zikmund-Fisher was told that without treatment he'd have about 10 years to live. The other option was a bone marrow transplant that had a 70 percent chance of curing him and ensuring a normal life.
"But the transplant itself — because of the chemotherapy, because of the infection risks — had roughly a 25 to 30 percent chance of killing me within six months to a year," Zikmund-Fisher says.
At the time, Zikmund-Fisher was 28, married, and had a child on the way. Ultimately, he made his life-or-death decision based on factors even he couldn't quantify.
He concluded that with no transplant and 10 years of life, he would get to know his then-unborn daughter, but she would remember him as a father in and out of hospitals. Those were not the 10 years he wanted. So he chose to gamble on the transplant.
"My experience, my outcome has been very positive," Zikmund-Fisher says. "I was on a hospital floor with 20 other patients, going through very similar procedures. Four of them never left the floor. I was one of the lucky ones."
What became apparent to Zikmund-Fisher was that probabilities, while useful, are quite limited in their ability to predict what will happen to any one person.
"We're never 95 percent alive. We either live or die. We experience outcomes," he explains. "On a population level, I can have 100 people in a room, and some will have something happen to them and some will not. And that's the hard part because if you happen to be the unlucky one who has that rare event happen to you, you still have the bad thing happen to you in its full awfulness."
Still, Zikmund-Fisher says, when it comes to medical treatment, it's important that doctors think about the overall numbers — not individual cases.
"A doctor doesn't see one patient. They see hundreds of patients — thousands of patients — over their career. We want doctors to make choices that give all of their patents the best possible outcomes regardless of whether that particular choice turned out well in the last time they tried it, or turned out poorly," he says. "We want doctors to take the long view, to give us the best chances of success, knowing that sometimes it's going to work well, and sometimes it's not."
On a personal level, Zikmund-Fisher acknowledges there's a harder reality.
"I only have one hand in this poker game. I only get one life," he says. "I can play the odds. I can try to give myself the best opportunities. But risk is a part of our everyday life, and rare things do happen, and we have to accept that."
This is part one of an All Things Considered series on Risk and Reason.
ROBERT SIEGEL, HOST:
Every day we confront choices that have been quantified for us - expressed as probabilities. Little choices like do you take an umbrella or do you buy a lottery ticket? And big choices - imagine facing this kind of choice - do one thing and it might mean you will die very soon or it might mean you'll live for decades in good health. Do another thing and it might mean that your health will decline and you'll die in a few years. And to each of those possibilities there is a percent likelihood attached. That's the kind of choice Brian Zikmund-Fisher faced.
BRIAN ZIKMUND-FISHER: My story begins with being discovered while I was in graduate school actually with a blood disorder called Myelodysplastic Syndrome that causes your body to fail to produce blood cells the way it should and in my case, made me be much more susceptible to bleeding. We found it because I got a huge bruise up and down my left arm after I was playing racquetball.
SIEGEL: Brian was 28. For months he got platelet transfusions every eight days. That helped but the benefit was limited without major treatment, Brian was told, he had about 10 years to live. At the time, his wife was pregnant with their first child. The major treatment he could take was a bone marrow transplant and his doctor said the probability was good that the transplant would cure him.
ZIKMUND-FISHER: And that that good probability was about 70 percent chance. So if I did the transplant I would have a 70 percent chance of having a long life but the transplant itself - because of the chemotherapy, because of the infection risks - had roughly a 25 to 30 percent chance of killing me within six months to a year.
SIEGEL: At the time, you said you were a graduate student.
SIEGEL: Your field of study?
ZIKMUND-FISHER: I was a graduate student in social and decision sciences, studying how to make complex decisions.
SIEGEL: Brian Zikmund-Fisher says he applied his own intellectual discipline to the biggest choice of his life - with all the numbers in-hand.
ZIKMUND-FISHER: But even with those numbers it was an incredibly difficult task. It was going to be decided based upon truly understanding my own values and whether I could live with the possible outcome of having the transplant not work.
SIEGEL: And his dying within a year. Brian Zikmund-Fisher decided on the basis of factors that you just can't quantify - it was all about his family. He concluded that with no transplants and 10 years of life he would get to know his then unborn daughter but to her he would likely be an invalid - a father in and out of hospitals and those weren't the 10 years that he wanted. So rather than the sure but unsatisfying course, he chose to gamble. He had the bone marrow transplant 15 years ago.
ZIKMUND-FISHER: My experience, my outcome has been very positive. I was on a hospital floor with 20 other patients going through very similar procedures. Four of them never left the floor, I was one of the lucky ones.
SIEGEL: That experience drove home the reality that probabilities while useful are limited in their ability to predict what will happen to any one person.
ZIKMUND-FISHER: We're never 90 percent alive. We either live or die. We experience outcomes. On a population level, of course, I can have 100 people in a room and some will have something happen to them and the others will not. And so it's that population level idea of risk that we try to apply to an individual when we talk about probability.
SIEGEL: Which as you say is essentially ill fitting at some level since I am not a population.
ZIKMUND-FISHER: No you're not. And that's the hard part because if you happen to be the unlucky one who has that rare event happen to you, you still have the bad thing happen to you in its full awfulness.
SIEGEL: Regardless of whether that was a 2 percent chance or an 80 percent chance.
ZIKMUND-FISHER: Exactly, right.
SIEGEL: All this week, we're going to explore question - how well do we understand and act on the probabilities we're presented with? Can numbers have a president make a life or death policy decision? Can they help us weigh medical options less drastic than one Brian faced? Brian Zikmund-Fisher now teaches about risk and probability at the University of Michigan school of Public health. The influence of his personal experience on his own academic work...
ZIKMUND-FISHER: Oh, I think the first thing it left me with was an understanding of how challenging it is for a doctor - who is by their very nature playing with risk over time - right? A doctor doesn't see one patient, they see hundreds of patients, thousands of patients over their career. And we want doctors to make choices that give all of their patients the best possible outcomes regardless of whether that particular choice turned out well in the last time they tried it or turned out poorly. We want doctors to take the long view to give us the best chances of success knowing that sometimes it's going to work well as sometimes it's not. I also took away from it the reality that I only have one handedness poker game. I only get one life and I can play the odds. I can try to give myself the best opportunities - but risk is a part of our everyday life. And rare things do happen. And we have to accept that.
SIEGEL: That's Brian Zikmund-Fisher of the University of Michigan. Tomorrow, what does it mean that there's a 20 percent chance of rain? Transcript provided by NPR, Copyright NPR.