https://www.infirmiere-canadienne.com/blogs/ic-contenu/2015/05/02/terminologie-101-reduction-du-risque-dans-les-ecr
May 02, 2015, By: Maher M. El-Masri, RN, PhD
Risk reduction: The percentage of reduction in the risk of an outcome as a result of the intervention in an RCT
Source: Guyatt, G., Rennie, D., Meade, M. O., & Cook, D. J. (Eds.). (2008). Users’ Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice (2nd ed.). New York: McGraw-Hill
The goal of randomized controlled trials (RCTs) is to examine the effect of a treatment on an outcome by comparing the difference in the rate of the outcome in an intervention group and in a control group. If the goal of the RCT is to reduce the likelihood of a negative outcome, such as infection, the effect is reported within the context of risk reduction. If the goal of the RCT is to increase the likelihood of a positive outcome, such as successful discharge, the effect is calculated within the context of benefit increase. Given that the difference between risk reduction and benefit increase is a semantic one, our discussion will focus on risk reduction.
A common way to report risk reduction is in terms of either absolute risk reduction (ARR) or relative risk reduction (RRR). ARR is the simple arithmetic difference resulting from subtracting the rate of the outcome in the intervention group (i.e., the experimental event rate or EER) from the outcome rate in the control group (i.e., the control event rate or CER). RRR, in contrast, is a proportional measure: it is the product of dividing the ARR by the CER.
Let us assume that an RCT examines the impact of discharge teaching on the risk of hospital readmission among patients with congestive heart failure. The CER of readmission among patients who received standard discharge teaching (the control group) is 15 per cent, while the EER of hospital readmission among patients who received individualized discharge teaching (the intervention group) is 10 per cent. One can calculate the ARR of hospital readmission by subtracting the EER from the CER, yielding an ARR of five per cent. The RRR, in contrast, is 33 per cent (ARR/CER = 0.05/0.15 = 0.33). The RRR of 33 per cent means that a patient who receives the treatment should expect a 33 per cent reduction in his/her likelihood of readmission in comparison to a patient who doesn’t receive the treatment. Note that the ARR (5%) constitutes one-third (33%) of the 15 per cent readmission rate in the control group. The ARR is useful to inform patients of the reduction they should expect in their pre-treatment rate of the outcome as a result of the treatment, while the RRR is useful to help patients gauge the proportional reduction in this rate relative to the rate among those who do not receive the treatment.
ARR and RRR are equally important measures of risk reduction in RCTs. However, as can be seen from our example, the RRR can yield a more impressive number than the ARR, and researchers have misused it to exaggerate the true effect of an intervention. Thus, proper interpretation of these measures is vital.
NurseONE.ca resources on this topic
MyiLibrary
- Crosby, R. A., DiClemente, R. J., & Salazar, L. F. (Eds.). (2006). Research Methods in Health Promotion.
- Maltby, J., Williams, G. A., McGarry, J., & Day, L. (2010). Research Methods for Nursing and Healthcare.
- Mateo, M. A., & Kirchhoff, K. T. (Eds.). (2009). Research for Advanced Practice Nurses: From Evidence to Practice.
Maher M. El-Masri, RN, PhD, is a full professor and research chair in the faculty of nursing, University of Windsor, in Windsor, Ont.
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