Saturday, May 28, 2016

Risky Business: Framing Statistics

The Gist: Medical literature frequently frames effect size using relative and absolute risks in ways that intentionally alter the appearance of an intervention, an example of framing bias. Effect sizes seem larger using relative risk and smaller using absolute risk [1,2].

Part of our 15 Minutes - 'Stats are the Dark Force?' residency lecture series
Risk from Lauren Westafer on Vimeo.

Perneger and colleagues surveyed physicians and patients about the efficacy of 4 new drugs. They were presented with the following scenarios:
While these numbers reflect the same data, patients and physicians selected that the drug that "reduced mortality by 1/3" was "clearly better" [3].  This indicates both parties are susceptible to the cognitive tricks statistics, particularly the way that relative risk make numbers appear larger and the ways absolute risk makes numbers appear smaller.  Authors can consistently switch between relative and absolute risk to maximize the appearance of benefit and minimize risks, as seen in the following abstract:

Perhap authors should be encouraged to report statistics consistently, using relative OR absolute rather than switching between the two to give the appearance of maximum benefit and minimal risk.

References:
1. Barratt A. Tips for learners of evidence-based medicine: 1. Relative risk reduction, absolute risk reduction and number needed to treat. Canadian Medical Association Journal. 171(4):353-358. 2004
2. Malenka DJ, Baron JA, Johansen S, Wahrenberger JW, Ross JM. The framing effect of relative and absolute risk. Journal of general internal medicine. 1993;8(10):543-8.
3. Perneger TV, Agoritsas T. Doctors and patients' susceptibility to framing bias: a randomized trial. Journal of general internal medicine. 26(12):1411-7. 2011.

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