April 30th, 2014
Thinking About Risk
The new ASCVD risk and lipid guidelines created quite a stir. People have questioned the accuracy of the risk calculator and the wisdom of giving statins to people above the 7.5% 10-year risk threshold. We have had a very robust and good discussion. But I have been wondering about how our patients will perceive their risk. Will they truly understand what we mean when we give them an estimate of their 10-year risk? It is conceptually easy to talk about an LDL target, but it is much harder to understand one’s 10-year risk of a cardiovascular event. The difficulty of wrapping one’s head around the concept of risk may be part of what is driving the controversy over the risk guidelines.
One way to visualize the idea of individual risk is to use an image of a roulette wheel. Imagine that each of us has one spin of our own roulette wheel and that spin will determine our 10-year cardiovascular outcome. We can change the design of our own roulette wheel to reflect our own 10-year cardiovascular risk.
Imagine a wheel with 50 spaces, some dark, representing bad outcomes, and the others red, representing good outcomes. Increasing the risk increases the number of dark spaces. If we stop smoking, we can reduce the number of dark spaces by roughly half. If we start a statin, we can reduce the number of dark spaces by about 20%.
Figure A shows the roulette wheel for a 59-year-old African-American man with a total cholesterol of 220, HDL of 40, with untreated systolic blood pressure of 120, without diabetes, who smokes. The 10-year ASCVD risk is around 13%. If he stops smoking, his risk drops to 8%, as shown in Figure B. With statin treatment, the risk drops further to about 6%, as shown in Figure C. The roulette wheels give a visual demonstration of the absolute and relative risks. If you had just one spin of the wheel, which wheel would you prefer to use? Are you willing to take a statin for 10 years to go from the wheel in Figure B to the one in Figure C?
Figure A Figure B Figure C
Risk is another word for probability, something that isn’t always easy for people to think about. Some consider it to be the observed frequency of an outcome, measured repeatedly over the long-run. Pictorial displays of little icons can visually show this notion of probability, but they don’t display what is really going on with the risk calculator. Others use a Bayesian or subjective notion, where probability is one’s degree of belief that a particular outcome will occur. A third example is to view probability from a design point of view. How we design a roulette wheel, a coin, a die, or a lottery can determine the frequency of events over the long-run, or our degree of belief about the outcome for a single individual. We can design our own roulette wheel through risk factor modification. As the saying goes, we can make our own luck.
The roulette wheel analogy may help us wrap our heads around the concept of individual risk and explain this concept to our patients. To read more about risk, I highly recommend a new book called Risk Savvy: How To Make Good Decisions by Gerd Gigerenzer.
How do you think about risk?