Risk Perception

Two Pathways

Expert quantifications of morbidity or mortality risks posed by medical conditions or procedures are based on objective data and/or theoretical models. The general public can evaluate the same options very differently, sometimes with serious consequences. Public perception of an autoimmune disease risk of silicone breast implants, for example, resulted in bankruptcy for the manufacturer, despite no scientific evidence of implant-related illnesses. Neuroscience and behavioral research show that risk perception is determined by both analytic and emotional processes. The relative balance of these two pathways is affected by professional training and cognitive capacity. While emotional processes are hardwired and automatic, analytic evaluations are effortful and need to be learned.

Risk as a Statistic

Actions that result in a guaranteed, known outcome are typically described as riskless. The more disparate the range of possible outcomes, the more risky the action. This greater sense of unpredictability of outcomes is captured by the variance as a statistical index of degree of risk:

where x denotes the possible outcomes, p(x) the probability that each outcome will occur, and EV(x) the expected value of these outcomes.

Take the hypothetical example of two cancer treatments, surgery and radiation, which offer different prospects of extending life. Surgery entails a 10% chance of death during the procedure but a 90% chance of extending life by 10 years. The average or expected life extension of surgery therefore is EV(Surgery) = .10(0) + .90(10) = 0 + 9 = 9, and its variance is Variance(Surgery) = (0 − 9)2(.1) + (10 − 9)2(.9) = 81(.1) + 1(.9) = 8.1 + .9 = 9. Radiation has no chance of immediate death but offers shorter life extensions. Half of the patients live for 2 additional years, and the other half for 5 additional years, so the expected life extension is EV(Radiation) = .50(2) + .50(5) = 1 + 2.5 = 3.5, and its variance is Variance(Radiation) = (2 −3.5)2(.5) + (5 − 3.5)2(.5) = 2.25(.5) + 2.25(.5) = 2.25. While radiation offers a shorter average life extension than surgery (3.5 years as opposed to 9 years), it also has a smaller variance (2.25 vs. 9), that is, less uncertainty or risk about the outcome.

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