# Absolute risk reduction  Main Article Discussion Related Articles  [?] Bibliography  [?] External Links  [?] Citable Version  [?] This editable Main Article is under development and subject to a disclaimer. [edit intro]

In clinical epidemiology and evidence-based medicine, the absolute risk reduction is a measure that compares the frequency of a clinical outcome in group of patients exposed to a factor compared to a control group of patients. This measure should be contrasted with the relative risk reduction.

Most scientific journal articles fail to report absolute measures which may lead to exaggerated perceptions of results.

## Calculations

Two-by-two table for a randomized-controlled trial or cohort study
Outcome
Present Absent
Experimental group Cell A Cell B Total in the experimental group
Control group Cell C Cell D Total in the control group
Total with the outcome Total without the outcome
$\displaystyle \mbox{Experimental event rate EER)} =\left (\frac{\mbox{ Cell A}}{\mbox{Total in the }experimental\mbox{ group}}\right )$
$\displaystyle \mbox{Control event rate (CER)} =\left (\frac{\mbox{Cell C}}{\mbox{Total in the }control\mbox{ group}}\right)$
$\displaystyle \mbox{Absolute risk reduction} =\left (\mbox{CER - EER}\right)$

### Confidence intervals

The confidence intervals can be calculated using the method of Daly:

$\displaystyle \mbox{Standard error} =\sqrt{\left(R_1 \times\frac{1-R_1}{N_1}\right) + \left(R_2 \times\frac{1-R_2}{N_2}\right)}$
$\displaystyle \mbox{Confidence intervals} = \mbox{Absolute risk reduction} \pm 1.96 \times \mbox{Standard error}$