Why doctors are so bad at predicting how long their patients will live.

Health and medicine explained.
Aug. 18 2010 11:37 AM

The Worst Fortune Tellers

Why doctors are so bad at predicting how long their patients will live.

Lockerbie bomber Abdelbaset Ali Mohmet al-Megrahi. Click image to expand.
Lockerbie bomber Abdelbaset Ali Mohmet al-Megrahi (center)

A year ago, U.K. officials released convicted Lockerbie bomber Abdelbaset Ali Mohmet al-Megrahi to Libya on humanitarian grounds, after doctors predicted that he had just three months to live. The British cancer expert whose opinion heavily influenced the decision, Karol Sikora, recently owned up to his miscalculation, telling a London paper, "There was always a chance he could live for ten years, twenty years. ... But it's very unusual." Lockerbie victims'families blasted the decision to release al-Megrahi, and the issue was placed on a short list of U.S. concerns in a recent meeting between President Obama and new British Prime Minister David Cameron. This week, Sikora acknowledged his flawed assessment to the U.K.'s Observer. "If I could go back in time I would have probably been more vague and tried to emphasize the statistical chances and not hard fact," he said, later adding, "Initially I thought he had 18 months, but when I saw the data, the blood tests and X-ray reports and spoke to the prison doctor, who had observed the pace of the disease, I thought it would be much quicker."

Which raises the obvious question: How did Dr. Sikora get it so wrong?

Doctors are notoriously poor at predicting life span, even when they're dealing with the terminally ill (defined as a prognosis of six months or less). In the case of al-Megrahi, the governments of the United Kingdom and Libya were both interviewing experts to determine how much longer the prisoner had to live. Under normal circumstances, however, it takes some badgering to even get a doctor to offer a prognosis. Doctors prefer not to prognosticate for three reasons: We don't like to be wrong; we don't want to take away hope for survival or good quality of life in the time that remains; and we just aren't adequately trained to do it. And our reluctance to make such guesses means that when we do try to predict the future, we're pretty lousy at it.

Almost every doctor can tell you a story of a patient living months or even years longer than expected. An oncologist colleague of mine, for example, sent a patient with prostate cancer to hospice with "a prognosis of less than six months. … Almost two years later, I saw him at his son's wedding." This was no doubt a joyous occasion. Yet these results are not typical: In the few studies that have investigated physicians' abilities to prognosticate death, doctors usually overestimate survival time by at least twice as much. There are many theories to explain this, chief among them that doctors tend to be overly optimistic with patients they've known and treated for a long time.

Call us actuarially-challenged. Data on survival are available, especially for chronic and well-studied conditions like  cancer  or  heart disease. Al-Megrahi, the Lockerbie bomber, is reported to have metastatic (advanced) prostate cancer, a diagnosis with a median survival of 18 months, but one with a variance as wide as half a decade or more. Since doctors typically avoid making predictions, these tools are infrequently dusted off and put to use. Our collective reluctance to offer patients a prognosis makes us less accurate in the rare instances we actually do it.

In his seminal book  Death Foretold: Prophecy and Prognosis in Medical Care, Nicholas Christakis, a medical doctor and sociologist, argues that medical science has given the processes of diagnosis and treatment disproportionate emphasis in the educational curricula of doctors. He examined major medical textbooks that have been used by medical students (and practicing physicians) for decades and determined that the relative percentage of space for each disease entity devoted to prognosis diminished with each subsequent edition, often to a paragraph or less. Furthermore, he writes that avoiding prognosis is a professional norm for doctors at all levels of training. In our research, teaching, and communication, we focus almost exclusively on the ever-expanding sciences of diagnosis and treatment, leaving prognosis almost entirely to the side.

Making predictions about the lives of al-Megrahi and other cancer patients can be particularly tricky. William Dahut, clinical director of the Center for Cancer Research at the National Cancer Institute, blames "a general lack of understanding of the specific biology of the cancer as well as a general lack of understanding of the biology of the individual." Doctors and scientists often refer to an individual's biology as "host factors," making allowances for the fact that patients are indeed different—in immunity, resilience, and attitude. The difficulty in accounting for such differences is another reason that predictive accuracy is so low.

About the only time that doctors seem to accurately be able to prognosticate impending death is near the very end of life. Predictions at this stage range from hours to days. To paraphrase Justice Potter Stewart, a doctor can tell you when a patient is very near death because "we know it when we see it." This usually involves a patient's choice (or a family member's, if the patient is incapacitated) to forgo life-sustaining technology like a mechanical ventilator ("breathing machine").

Such technology can complicate predictions further: Take former Vice President  Dick Cheney, who last month had a left ventricular assist device implanted in his chest to augment the pumping of his weakened heart. By conventional measures, given the severity of his reported  congestive heart failure, the likelihood of his surviving past one year would be only 50 percent. But don't yet file his obituary: Doctors not involved with his treatment have given optimistic projections that carefully selected patients with LVADs can live more than an additional year with the device; one patient survived more than five.

So how do we become better at prognostication?

Christakis argues that studying and delivering prognoses to patients is part of the ethical obligation of doctors to their patients. "Furthermore," he writes, "physicians should legitimate discussions regarding prognosis not only with their patients but with each other." As such, doctors would recast the professional norm to include open and frank discussion of prognosis in medical care.

In so doing, we need to strive for honesty and avoid "hanging crepe," the idea of delivering a poor prognosis simply to combat our tendency to be overly optimistic and to keep our hands clean: If the patient dies, I predicted it and therefore appear accurate; if the patient outlives my prediction, everyone is pleasantly surprised and thus I'm not held accountable. Dahut reminded me of the oncologist's rule of thumb: If a patient was walking around three months ago and still can, he'll probably be around a little while longer; if he can't get out of bed, "the disease is likely to progress at the same rate." Framing it this way helps patients and families manage expectations, by not giving a limited time interval that can feel like either an immutable sentence or an obstacle to overcome.

Beyond that, there needs to be fundamental change in the way that doctors are educated in prognosis calculation and delivery. Prognosis should not be left to the realm of mordant comments in pathology lectures or sotto voce remarks to students and residents outside a patient's room during ward rounds. Instead, medical education at all levels should feature actuarial information on the major causes of death, with modification for the age of the patient and the various treatment options. Patients will have to more overtly demand prognosis to help spur these changes.

Of course, in an age of patient empowerment, you may well be the ones to lead the charge to make doctors more attuned to answering that fundamental question, which lies at the very heart of medical practice. We can only hope that future doctors will be better prognosticators than old Dr. Sikora.

Like Slate on Facebook. Follow us on Twitter.

TODAY IN SLATE

Foreigners

More Than Scottish Pride

Scotland’s referendum isn’t about nationalism. It’s about a system that failed, and a new generation looking to take a chance on itself. 

What Charles Barkley Gets Wrong About Corporal Punishment and Black Culture

Why Greenland’s “Dark Snow” Should Worry You

Three Talented Actresses in Three Terrible New Shows

The Human Need to Find Connections in Everything

It’s the source of creativity and delusions. It can harm us more than it helps us.

Jurisprudence

Happy Constitution Day!

Too bad it’s almost certainly unconstitutional.

Is It Worth Paying Full Price for the iPhone 6 to Keep Your Unlimited Data Plan? We Crunch the Numbers.

My Father Was James Brown. I Watched Him Beat My Mother. Then I Married Someone Like Him.

  News & Politics
Weigel
Sept. 17 2014 12:02 PM Here It Is: The Flimsiest Campaign Attack Ad of 2014, Which Won't Stop Running
  Business
Moneybox
Sept. 17 2014 12:13 PM “For a While Liquidity Led to Stupidity”
  Life
The Eye
Sept. 17 2014 12:19 PM Early Cancer Hospitals Were Modeled on French Castles, Served Champagne
  Double X
The XX Factor
Sept. 15 2014 3:31 PM My Year As an Abortion Doula
  Slate Plus
Slate Fare
Sept. 17 2014 9:37 AM Is Slate Too Liberal?  A members-only open thread.
  Arts
Behold
Sept. 17 2014 11:06 AM Inside the Exclusive World of Members-Only Clubs
  Technology
Future Tense
Sept. 17 2014 11:14 AM How Does That Geometry Problem Make You Feel? Computer tutors that can read students’ emotions.
  Health & Science
Bad Astronomy
Sept. 17 2014 11:18 AM A Bridge Across the Sky
  Sports
Sports Nut
Sept. 15 2014 9:05 PM Giving Up on Goodell How the NFL lost the trust of its most loyal reporters.