The relative reduction in risk (RRR) for an intervention, usually expressed as a percentage reduction from the risk of the comparison intervention, is commonly used as the primary result of clinical trials. The anticipated reduction in the primary outcome measure for the trial will be used to calculate the study sample size, in order to achieve a RRR that rejects the null hypothesis of no difference (RRR=0) at a required level of significance. The RRR is calculated as the difference in risks between the two interventions, divided by the risk of the comparison therapy (x 100 to convert it into a %). In modelled economic evaluations RRRs are frequently used as the measure of effect (and the confidence intervals for RRR provide a distribution for this measure, usually assumed to be Normal), however the RRRs need to be associated with absolute levels of risk in order for incremental values (health outcome or cost) to be calculated.

How to cite: Relative Risk Reduction [online]. (2016). York; York Health Economics Consortium; 2016. https://www.yhec.co.uk/glossary/relative-risk-reduction/

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