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As people become more involved in managing their own health care, they’re increasingly having to assess the risk of taking medications that have side effects. A researcher at the Haskayne School of Business has found that people are terrible at assessing risk when presented with both a high and lower probability of adverse side effects for a drug — a misperception that can have serious consequences for the person’s welfare.

“It's no longer the case that the doctor just tells you what to do,” says Dr. Mehdi Mourali, PhD, associate professor of marketing at Haskayne. “We are in a model of shared decision-making where you're supposed to discuss the risks and benefits of different treatments with your doctor and then ultimately it's the patient who chooses.”

In ","�� Mourali and his colleague, Dr. Zhiyong Yang, PhD, of Miami University found that people often hold mis-calibrated risk perceptions, especially when they have to combine multiple risks.

“We're all pretty good at judging single risks. if you tell me, this treatment has a 50 per cent chance of causing something bad, I know what that means.” But, he says, as soon as you add a second risk and people have to combine the two, their calculus goes off the rails.

“If you take this medication, you have a 50 per cent chance of developing headaches, that's a high risk. But if I told you that in addition to the risk of headaches, there is a one per cent chance that you will experience stomach cramps, that's a second side effect, but it's low risk.”

Rather than adding these risks together, people tend to average them out. This means they consistently judge a medication with one high-probability and one low-probability side effect to be less risky overall than a medication with just the high-probability side effect.

“We find that adding a low-risk side effect to a medication associated with a high-risk side effect increases consumers’ likelihood to start the medication,” says Mourali. “Consumers are more willing to take the objectively riskier drug because they misperceive it to be safer.”

This holds true regardless of people’s skill with numbers. “We measured numeracy, how comfortable people are with numbers, and that didn't seem to affect this problem,” he says.

People across the board seem to evaluate a mixed option slightly lower than one that only has the higher risk.  

The researchers found that presenting multiple risks with graphics can improve risk perception and reduce the willingness to take the medication. “If we show them a graph, for example, with stacked bars — one bar shows the high risk, and then on top of that we stack the low risk — they realize they should be adding these risks, not subtracting or blending them.”

Understanding how people perceive and process numerical risks has important implications for designing effective risk communications and helping people make better decisions about medications.

“In order for you to make an informed decision, you need to understand the risks and the benefits involved,” he says. “And what we found is that it's not really clear people always understand the risks.”