Understanding Risk – Ordered Weighted Averaging and Relative vs Absolute Risk Reduction – GIS2 at Ryerson

Now, think of the corona crisis. Are we pursuing a balanced response, as recommended by a group of Canadian infectious disease experts in July 2020? Many readers will probably think of government restrictions as a risk-averse strategy—designed to slow the spread of SARS-CoV-2 and reduce the expected strain on the health-care system. Given that large-scale lockdowns are an unprecedented public health measure, and the collateral damage was either not expected or willingly taken into account, this approach however appears more risk-taking than risk-averse to me. The obvious inefficiency and illegitimacy of lockdowns, and the mission creep from “flattening the curve” to achieving the unattainable goal of #CovidZero, support their assessment as an extremely risk-taking strategy.

Calculation of relative and absolute risk reduction for COVID-19 vaccine trials. Data source: https://blogs.bmj.com/bmj/2020/11/26/peter-doshi-pfizer-and-modernas-95-effective-vaccines-lets-be-cautious-and-first-see-the-full-data/

…but in terms of publicly presenting and discussing the vaccine trial results, a 2019 article in the Drug and Therapeutics Bulletin is revealing. Box 3 explains the difference between absolute and relative risk reduction. Note the author’s statement “Relative risks, then, can exaggerate the perception of difference, and this is especially prominent when the absolute risks are very small.” What would you think if the headlines about the trial successes had read “Shot Reduces COVID-19 Risk by 0.7%” instead of “COVID-19 Shot 95% Effective”? The author of “How to communicate evidence to patients”, Dr. Alexandra Freeman, advocates for reporting multiple metrics for better context. With respect to the ongoing pandemic, the powers that be should ensure transparent communication of scientific evidence. This also includes a host of other issues with the vaccine trials that Dr. Peter Doshi raises in the above-cited BMJ commentary.

Understanding Risk – Ordered Weighted Averaging and Relative vs Absolute Risk Reduction – GIS2 at Ryerson