A Cochrane Collaboration Review Confirms that People Overestimate the Benefits of Medical Interventions, When those Are Expressed Solely in Relative Terms — Using Absolute Numbers Enhances Understanding among Patients and Doctors

22 March 2011

Identical statistical data can be truthfully worded in ways that deceive

In my experience, medical studies and medical interventions often deceptively use relative risk reductions to mask the fact that the absolute risk of falling ill (or being cured) is already very low.

Pharmaceutical companies are perhaps the biggest culprits in this semantic deception. Wording medical study findings in terms of relative risk reduction makes their drugs seem far more effective among the population at large than they really are.

Medical professionals, like patients, regularly fall for the relative risk ruse.

What the Cochrane Collaboration review of literature said about this —

A recent Cochrane Collaboration review of medical literature concluded that:

Health professionals and consumers may change their choices when the same risks and risk reductions are presented using alternative statistical formats.

Based on the results of 35 studies reporting 83 comparisons, we found the risk of a health outcome is better understood when it is presented as a natural frequency rather than a probability.

On average, people perceive risk reductions to be larger and are more persuaded to adopt a health intervention when its effect is presented in relative terms (eg using relative risk reduction which represents a proportional reduction) rather than in absolute terms (eg using absolute risk reduction which represents a simple difference).

We found no differences between health professionals and consumers.

© 2011 Elie A. Akl et al., Using alternative statistical formats for presenting risks and risk reductions, Cochrane Database of Systematic Reviews, DOI: 10.1002/14651858.CD006776.pub2 (2011) (from “Summary”)

A good example of what these terms mean

Publisher Wiley-Blackwell and ScienceDaily provided an example:

[Y]ou could read that a drug cuts the risk of hip fracture over a three year period by 50%. At first sight, this would seem like an incredible breakthrough.

In fact, what it might equally mean is that without taking the drug 1% of people have fractures, and with the drug only 0.5% do.

Now the benefit seems to be much less.

Another way of phrasing it would be that 200 people need to take the drug for three years to prevent one incidence of hip fracture. In this case, the drug could start to look a rather expensive option.

Statisticians have terms to describe each type of presentation. The statement of a 50% reduction is typically expressed as a Relative Risk Reduction (RRR).

Saying that 0.5% fewer people will have broken hips is an Absolute Risk Reduction (ARR).

Saying that 200 people need to be treated to prevent one occurrence is referred to as the Number Needed to Treat (NNT).

Furthermore, these effects can be shown as a frequency, where the effect is expressed as 1 out of 200 people avoiding a hip fracture.

The review authors concluded that people understand frequencies better than relative and probability measures

Wiley-Blackwell and ScienceDaily quoted two of the study authors in this regard:

"People perceive risk reductions to be larger and are more persuaded to adopt a health intervention when its effect is presented in relative terms," said Elie Akl . . . first author on the review.

"Relative risk statistics do not allow a fair comparison of benefits and harms in the same way as absolute values do," said lead researcher Holger Schünemann . . . .

"If relative risk is to be used, then the absolute change in risk should also be given, as relative risk alone is likely to misinform decisions."

Conclusion — even when true, statistics can be used to obscure and deceive

As I have written before, much of medical research and some medical practice have been taken over by people who do not have patients’ best interests at heart.

Since we are mostly geared to think in absolute numbers, insist on getting your medical data that way. You might actually open your medical professional’s eyes, as well. Together, we can cut through some of the semantic nonsense that the disingenuous greedy try to foist on us.

The more you know and understand, the more sensibly you can choose what is best for you.

PeteFree.com

A Cochrane Collaboration Review Confirms that People Overestimate the Benefits of Medical Interventions, When those Are Expressed Solely in Relative Terms — Using Absolute Numbers Enhances Understanding among Patients and Doctors