RLO: Relative Risk Reduction (RRR) and Absolute Risk Reduction (ARR)

Interpreting the Results

Let us take a look at the data for the 2 trials more closely.

Consider the RRR for both trials. Would you be likely to recommend the use of Curit to prevent the occurrence of a heart attack in both population groups?

The RRR is the same for both trials and looks pretty impressive so we probably would.

Let us look at the ARR for both trials. Would you still recommend the use of Curit to prevent the occurrence of an outcome in both population groups?

Probably not. The results for trial 2 do not look quite as impressive.

Interpretation of results and subsequent decisions in patient care may differ depending on how they are presented. The RRR looks more impressive and can be more persuasive than the ARR.

This is because the RRR does not take into account the initial baseline risk of the outcome event, making an insignificant finding appear significant.

In order to be meaningful, the RRR should always be reviewed in context with the underlying incidence (baseline risk) of the event. A large difference between the RRR and the ARR occurs when the outcome is rare, ie: the baseline risk is low.

Data expressed as the RRR is popular with sales representatives and journal articles. Be aware and do not be fooled! Always check the ARR too.

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