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The truth about medicine: we usually overestimate the benefits and underestimate the harms

harms benefits medicine

The proportion of study participants providing a correct estimate, underestimate, or overestimate of the benefit of a medical Intervention. (Via JAMA Internal Medicine)

With every pill we swallow, with every operation and screening test we endure, there's a chance that the benefits we get might not outweigh the harms we expose ourselves to. Usually, though, we don't think about that. We focus on help rather than harm, and think more health care is better than less or no health care.

Now, a new JAMA Internal Medicine systematic review — of dozens of studies on patients' expectations — quantifies exactly how unrealistic we are when it comes to our medical care. It turns out we almost always see the glass as half full, despite the evidence that suggests we actually shouldn't.

Looking at 36 studies on a range of medical interventions — from cancer screening tests to medications and surgeries — a pair of Australian researchers discovered that, overwhelmingly, patients overestimated the benefits and underestimated the harms.

In the 32 studies that looked at how patients perceived the benefits of a medical intervention, most (65 percent) overestimated them. On the other hand, the studies that looked at patients' perceptions of harms found a majority (67 percent) underestimated them.

This means when we walk into hospitals and clinics and sign up for tests, treatments, and procedures, we are unrealistically optimistic. And we too often forget about the possible downsides of the things we're exposing ourselves to.

The researchers found this was as true for our notions about the accuracy and helpfulness of mammograms and Pap smears as it was for our ideas about the medications — like hormone therapy — we take, and even the usefulness of ultrasounds to detect fetal problems in pregnancy.

"Participants rarely had accurate expectations of benefits and harms," the study authors wrote, "and for many interventions, regardless of whether a treatment, test, or screen, they had a tendency to overestimate its benefits and underestimate its harms."

This "optimism bias" is driven by several factors, the study authors contend: the marketing practices of industry, doctors' failure to communicate with patients about risk-benefit ratios, and the hopefulness and trust we place in health care and the medical profession.

Unrealistic expectations are having knock-on effects, the authors continue, driving our desire for more care instead of less, even when it confers no help and it may in fact hurt us. They suggest that this is "undoubtedly contributing to the growing problem of overdiagnosis and overtreatment."