Absolute Risk Reduction (ARR) - Definition and Calculation

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Our 2x2 sample table allows for quick calculations of up to 25 different biostatistics. Simply enter the required data into the highlighted boxes and the solution will appear. All of the most important equations are here – from absolute risk reduction to odds ratio to specificity.

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Key Concept:

So you want to change a patient’s current therapy because a new medication has a decreased risk of a particular side effect. That sounds reasonable, but have you taken other issues into consideration (e.g., efficacy, other adverse reactions, cost, etc.)? And how about the number needed to treat? Do you know how many patients would need to receive the new therapy as opposed to the old one before one patient less experiences the side effect? Determining the number needed to treat can be useful in clinical practice when analyzing the risk versus benefit between two therapies.

Absolute Risk Reduction
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Definition
Absolute risk reduction is the decrease in incidence of a condition or illness due to an activity, lifestyle modification, or therapy.

Equation
[ C / (C + D) ] - [ A / (A + B) ]

Calculation
It is calculated by subtracting the incidence of a condition in individuals in one treatment group by the incidence of the condition in individuals in another group.