In a study where Rivaroxaban was compared to enoxaparin to find total VTE following HIP replacement surgery, there were 17 total VTE out of 1513…

The Relative Risk Reduction (RRR) quantifies the percentage by which the risk of an outcome is reduced in the intervention group compared to the control group.

1. Calculate the event rate (risk) in each group:

Risk in Rivaroxaban group (intervention): 17 / 1513 ≈ 0.0112 (1.12%)

Risk in Enoxaparin group (control): 57 / 1473 ≈ 0.0387 (3.87%)

2. Calculate the Relative Risk (RR):

RR = (Risk in intervention group) / (Risk in control group) = 0.0112 / 0.0387 ≈ 0.29

3. Calculate the Relative Risk Reduction (RRR):

RRR = 1 - RR = 1 - 0.29 = 0.71

As a percentage, RRR is 71%.

A. 39%: This is an incorrect calculation, potentially resulting from misapplication of the risk values in the formula.

C. 29%: This value represents the Relative Risk (RR), which is the ratio of the risks, not the reduction in risk.

D. 14%: This is an incorrect calculation and does not correspond to a standard biostatistical measure in this context.

E. 42%: This is an incorrect calculation, possibly confusing RRR with another statistical measure like absolute risk reduction.

1. Guyatt

G.

Rennie

D.

Meade

M. O.

& Cook

D. J. (2015). Users' Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice (3rd ed.). McGraw-Hill Education. Chapter 13

"Therapy (Harm)

" section on "Measures of Association

" discusses the calculation of Relative Risk and Relative Risk Reduction.

2. Barratt

A.

Wyer

P. C.

Hatala

R.

McGinn

T.

et al. (2004). Tips for Learners of Evidence-Based Medicine: 1. Relative risk and odds ratios. Canadian Medical Association Journal

171(4)

353–358. https://doi.org/10.1503/cmaj.1021196. (This article defines RRR as 1 - RR on page 354).

3. University of California

San Francisco. (n.d.). Interpreting Proportions and Risk. UCSF School of Medicine

Training in Clinical Research Program Courseware. Retrieved from https://ticr.ucsf.edu/courses/briefcourses/docs/Proportions.pdf (This document provides the formula for RRR = 1 - RR on page 4).