Absolute Risk Reduction versus Relative Risk Reduction: Is One Better for COVID vaccines?

In this video, Dr. Roger Seheult of MedCram explains what the difference is between absolute risk reduction (ARR) versus relative risk reduction (RRR). Dr. Seheult provides examples on how to calculate the relative risk reduction and how to calculate the absolute risk reduction.

How to calculate ARR vs RRR

The relative risk reduction is calculated by the difference between the placebo group and the intervention group divided by the total number of occurrences in the placebo group. The absolute risk reduction is calculated by taking the difference between the placebo group and the intervention group but this time dividing it by the total number in the placebo group. It must be noted and cannot be emphasized enough that the absolute risk reduction is very much dependent on the prevalence of a disease unlike the relative risk reduction. 

Number needed to treat calculation

The number needed to treat (NNT) is the reciprocal of the absolute risk reduction, i.e.1 divided by the ARR.

How does prevalence affect ARR vs RRR

If a disease has a prevalence that is not changing frequently, it is reasonable to use either ARR or RRR depending on what is trying to be emphasized when reporting statistics.  However, ARR is very heavily dependent on the prevalence of a disease and can vary especially if the disease prevalence is changing frequently such as in a pandemic. The higher the prevalence of the disease or risk, the greater the ARR will be in comparison to a lower prevalence of disease or risk,  where the ARR can be lower. This occurs despite the RRR remaining the same for both cases.   

From the University of Western Australia, they have a diagram that states, “the absolute risk reduction is dependent upon the baseline risk of the study population or the individual patient.”  

Example of ARR and RRR

An example is using a 20% off coupon. This 20% can be viewed as the relative risk. If you apply this to a $1 item you save 20 cents, but if you apply it to a $1000 item you can save $200. These cost savings or absolute risk reduction can be as little as 20 cents or as high as $200 depending on the cost (or prevalence) of an item (or disease). 

Vaccines and ARR vs RRR

In regards to vaccines, the Pfizer studies were done during a low prevalence of COVID-19 whereas the J&J studies were done during a higher prevalence. As a result, understanding ARR, you can already surmise that the ARR in the J&J studies will be higher than in the Pfizer studies due to the increased prevalence of the disease.  However, the RRR would be expected to remain consistent across the board as it relates to the intervention. 

This is the reason why ARR is not a good measure of an intervention in a disease that changes prevalence frequently such as in a pandemic.  ARR is great to use in static diseases such as diabetes, stroke, coronary artery disease, vascular disease, etc. With vaccines, it takes time to get immunized. Vaccines are taken to prevent a disease somewhere down the line. In a pandemic, you will get absolutely different ARR depending on the prevalence of the disease during that time i.e. during a surge, you can expect a high ARR but lower ARR in low prevalent times.

Many individuals who use these terms may be using them incorrectly and in an inappropriate context, so it is important for you to understand how these terms work so you can better understand the issue. 

LINKS / REFERENCES:

Importance of understanding relative vs. absolute risk reduction regarding COVID-19 vaccines (Peter Attia MD) | https://youtu.be/u1wEruG4jys

Incidence and relative risk of stroke in the diabetic and the non-diabetic population between 1998 and 2014: A community-based stroke register (PLOS) | https://journals.plos.org/plosone/art…

Relative Risk Reduction vs. Absolute Risk Reduction – Dr Malhotra – A CNM Talk Highlight (College of Naturopathic Medicine) | https://youtu.be/hb_oQox1YqE

Another Bit of Pandemic Fallout: The Weaponization of Absolute Risk Statistics (Absolutely Maybe) | https://absolutelymaybe.plos.org/2022…

Safety and Efficacy of Single-Dose Ad26.COV2.S Vaccine against Covid-19 (NEJM) | https://www.nejm.org/doi/full/10.1056…

Fact Check-Why Relative Risk Reduction, not Absolute Risk Reduction, is most often used in calculating vaccine efficacy (Reuters) | https://www.reuters.com/article/factc…

Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine (NEJM) | https://www.nejm.org/doi/full/10.1056…

Coronavirus (COVID-19) Cases (Our World in Data) | https://ourworldindata.org/covid-cases

 

All coronavirus updates are at MedCram.com (including more discussion on delta variant covid, COVID Delta, COVID children, natural immunity COVID 19, and more).

MedCram Update 46: https://youtu.be/EFRwnhfWXxo

MedCram Update 47: https://youtu.be/H1LHgyfPPQ8

MedCram Update 132: https://youtu.be/9OZZ6_M4OB0

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