Daniel's message for doctors

THE RESEARCH ON THE PSYCHOLOGY of decision-making by Daniel Kahneman (joint Nobel Prize Winner in Economic Sciences, 2002) is apposite to clinical practice. In parallel with Herbert Simon (winner of the same prize in 1978), Kahneman linked behavioural sciences with decision-making in economics. Intriguingly, experts in the dry science of economics are slowly becoming aware that human choices are not based on numbers alone. In conducting studies of decision-making, Kahneman found people’s choices often differed from those that would be expected based on numerical probabilities alone. He examined the influence on the decision-making process of risk perception, risk-avoiding and risk-seeking behaviour, aversion to loss, distortion by hindsight, lack of statistical awareness, framing of choices, previous memories, and worries about the future. In the sphere of clinical medicine, teasing apart the factors that influence choices is necessary if we are to understand what goes through the minds of both doctors and patients. In life-and-death situations, survival overrides all other factors, and choices are based on the highest chance of survival. But Kahneman (with his colleague Amos Tversky) showed that, when the likely outcomes are less momentous, human factors can weigh more heavily than probabilities. In some situations, for example, the threat of a loss has a greater impact on choices than the chance of an equivalent gain. Patients may be “loss-averse” in avoiding losing something important, such as their independence or their right to stay in their own home. In other situations, patients are not necessarily “risk-averse” — they may be willing to “take a chance on it” if the anticipated gain is large. Clinicians and patients accept high risks with low probabilities of success (say, in radical head-and-neck surgery for cancer) when the payoff from success is high.4 Such behaviour parallels chasing jackpots and buying lottery tickets “against the odds”. Quite apart from any health or financial motive, risk-taking has its own psychological payoff, which adolescent males relish.5 Losses disturb us emotionally, as we agonise retrospectively over whether they could have been avoided (“if only . . .”). We regret losses that flow from actions we have taken, such as buying shares that drop in value, more than from actions we could have taken but didn’t, like not buying shares that rose in value. Clinicians use many devices (eg, prophylactic antibiotics and anticoagulants) to reduce the threat of possible therapeutic loss from complications of treatment. They protect themselves from the threat, the regret and the losses from litigation by adopting defensive medicine and medical insurance. Humans don’t think probabilistically, especially at the upper and lower ends of the probability scale. For example, we are unable to meaningfully assess differences between 1% and 5%, or between 90% and 95%, in weighing our decisions. Kahneman and Tversky also showed that humans usually weight low probabilities too high and high probabilities too low relative to certainty. People tend to categorise some factors in “either/or” terms (say, that vaccination is either “safe” or “dangerous”), without incorporating any numerical likelihood in their choice. Another factor that can bias risk perception is fear and “imaginability” of a disaster. If you fall out of a boat, you may react dramatically to your fear of being attacked by a shark, even though you know the probability is extremely low. Kahneman was Professor of Psychology at Princeton University, where John von Neumann and Oskar Morgenstern had developed “expected utility theory” in 1944. This theory of decision-making, incorporating all the outcomes and consequences of a decision, provided mathematical frameworks for “game theory”, which underpinned strategic thinking during the Cold War.6 This quantification of risks, costs and benefits of medical decisions is still used in healthcare today, but may lack credibility with patients, who are expected to assign a number, or betting odds, to the relative benefit of an outcome of treatment they haven’t yet experienced. Rather than measuring outcomes, Kahneman and Tversky shifted the focus to measuring change — the gains and losses each individual experiences. Gains and losses have personal meanings to each of us, and are not objective, calculable units. Patients have difficulty assessing the value of a hypothetical treatment outcome, but they understand the known and the familiar. They don’t wish to lose what is predictable and comfortable in their lives for the sake of a potential gain that they are unable to visualise. The relative importance of gains and losses was further demonstrated when Kahneman and Tversky tested the effects on decision-making of how questions were “framed”. Phrasing a question around the concept of “saving lives” shifted choices towards risk-taking; the same probabilities phrased around “lives lost” induced risk-averse choices. Both patients’ and doctors’ perceptions of risk shifted according to how the choice between alternatives was phrased. Kahneman’s belief that numerical probabilities are the correct determinants of decision-making was one side of a “clinical versus statistical” war within the psychology of Daniel's message for doctors