Assessing risk, vol I: Doctors’ orders.

by Andreas Baumann

Humans seem to be immutably bad at assessing risk. Some risks are routinely underestimated, while others routinely are overestimated. People tend to differ, not only with respects to what risks they’re willing to take, but also to how they assess these risks.

Think about an offer of some cash reward for a one in a thousand chance of certain, immediate death. How much money would you take for that risk? When you ask people about this, many of them wouldn’t consent to a million dollars for a one-in-a-million-chance, despite the fact that those of us who regularly bike around in large, trafficked cities take far more intensive risks everyday (and with a lot lower compensation!).

It’s not that we’re unaware of the risks associated with everyday behaviour; they might not be very salient to us, but nonetheless we’re aware of them. People don’t smoke because they’re unaware of the numerous risks associated with this; they just disregard these risks (see for example CMAJ 2000)^1.

But, this is all a question of habit. What’s more interesting is that even professionals relatively often display a limited understanding of the distribution of risk within their own field of expertise ^2. One such example may be doctors and their evaluation and recommendations on provoked (medically indicated) abortions in response to teratogenic risks.

A teratogenic risk is a risk to the føtus under pregnancy. A lot of things poses teratogenic risks – smoking, drinking larger amounts of alcohol, some pharmaceuticals.

What’s interesting about this is – in surveys of physicians, it has been found that they tend to overestimate the teratogenic risk and recommend abortion more often than would be indicated under the current best assessment of the risk (Amer. J. Roentgenol. 2004; Teratology 1992; Pharmacy Practice 2008).

Why do the physicians overestimate these risks? One reason might be that they prefer to err on the side of caution: rather than face a patient given birth to a handicapped child (and the physician maybe facing a malpractice lawsuit for not advocating an abortion), they recommend that the patient have an abortion and begin a new pregnancy. If this is the case, one should expect the rate of overestimating teratogenic risk to be highest for drugs particularly potent in the first trimester because of the time discounting invoked^3. That, of course, invokes rational considerations on the part of the physician – which could be a debatable frame. I haven’t had the chance to assess whether or not the overestimation of teratogenic risk in the surveys referenced conform to this pattern.

However, another reason for overestimating might be that the same cognitive bias as with the example in the bet of one million dollars against a tiny chance of certain death: we tend to be more risk-averse to behaviour that we don’t know than to behaviour we face every day, because we update our risk models based on our experience. This would explain why people seem to downplay the adverse health effects of acetaminophen (Tylenol / Paracetamol) for pregnant mothers, while grossly overestimating the teratogenic and føtotoxic effects of cocaine use in pregnant mothers.

^1) Why do people then smoke? Maybe they lie when surveyed and they really don’t believe that smoking poses these risks. Maybe they don’t have the character to quit. Maybe they discount their future risk against present utility and choose to smoke. Or maybe, they’re just stupid.
^2 ) One obvious field is of course investors, but I feel that the example offered above gives a better illustration.
^3) It’s generally considered more invasive and traumatic to abort late in the pregnancy than early in the pregnancy.