Through blogs and comments, patients and experts explore what it takes to find good health care and make the most of it.

Understanding Risk: It's All Relative


Red meat consumption is associated with an increased risk of total, cardiovascular disease and cancer mortality' stated a study released by the Archives of Internal Medicine in April 2012. What do results like that mean for individuals? Should we all become vegetarians? A problem, states physician Jose Hernandez, M.D., is that 'in much of the media coverage of Harvard's red meat study, not once was an absolute number provided in interpreting the study's findings.'

Carolyn Thomas, of The Ethical Nag, helps clarifies the difference between absolute and relative risk and explains that knowing the difference could help us understand the significance of study results:

"Absolute risk is risk stated without any context. For example, you have a 50 percent chance of flipping a coin and getting heads. This risk is not compared to any other risk; it's just the actual probability of something occurring.

Relative risk is a comparison between different risk levels. For example, your relative risk for lung cancer is (approximately) 10 if you have ever smoked, compared to a non-smoker. This means you are 10 times more likely to get lung cancer. But the relative risk (or risk ratio) is not the same as an increase in risk. In fact, [increased risk] tells us nothing about the actual risk."

Gerd Gigerenzer, Ph.D., author of Calculated Risks: How to Know When Numbers Deceive You, adds that often 'patients do not understand the difference between relative and absolute risk reduction, and that they evaluate a treatment alternative more favorably if benefits are expressed in terms of relative risk reduction.

H. Gilbert Welch agrees that The Problem Is Relative: 'Numerous studies have shown that the general public has exaggerated perceptions of health risks they face ' as well as exaggerated expectations of the benefit of medical care.' Welch blames the confusion on how messages are framed by the media, that is, by using relative change: ''Forty percent higher' and '50 percent lower' are statements of relative change. While they are easy to understand, they are also incomplete. Relative change can dramatically exaggerate the underlying effect. It's a great way to scare people.

In What Are the Chances We Need to Understand Probability, CFAH President Jessie Gruman describes why understanding probability is essential if people are to find good health care and make the most of it:

Without an appreciation of probability, we are unable to make informed decisions: we can't understand what our risks are or their magnitude or what the chances are that a treatment will help or hurt us. Without some grasp of probability, the provisional nature of science and uncertainty of disease progression appear as merely products of luck'?¦Many people do not now possess these skills. Each of us eventually must.

But understanding risk is not just about numbers. The way that risk information is presented to patients by their health care team can influence their decisions about medical treatment. Alex Smith, M.D., of GeriPal cites a study in the Annals of Internal Medicine that found variation in what people think it means when a doctor tells them someone "has a 5 percent chance of surviving," or, that they "will definitely not survive,' with many people interpreting even these strong statements optimistically. The authors of the study acknowledge that 'there is much more to communicating accurate information than misunderstanding of numerical risks. Psychological factors play a huge role in how patients hear and interpret information.


More Blog Posts by Conversation Continues

author bio

Conversation Continues feature ongoing discussions or news on current health topics with links to related materials.  They are part of the Center for Advancing Health’s portfolio of free, evidence-based coverage of what it takes to find good care and make the most of it.

Tags for this article:
Inside Healthcare   Conversation Continues   Make Good Treatment Decisions  

Comments on this post
Please note: CFAH reserves the right to moderate all comments posted to the Prepared Patient® Blog. Any inappropriate postings will be removed.

No comments have been entered yet.