https://www.infirmiere-canadienne.com/blogs/ic-contenu/2015/06/03/terminologie-101-nombre-de-sujets-a-traiter-dans-l
Jun 03, 2015, By: Maher M. El-Masri, RN, PhD
Number needed to treat: The number of individuals who need to be treated with the experimental intervention to avoid one negative outcome or produce one positive outcome
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
A statistically significant finding in a randomized controlled trial (RCT) enables one to conclude that the observed difference in the outcome between the study groups is true. However, it is possible for a study to produce a statistically significant result that is associated with a minute effect, which will have little, if any, importance to clinicians. Therefore, the findings of RCTs should be judged on both their statistical significance and their clinical significance. The effect of an intervention needs to be clinically convincing if health-care providers are to endorse it as an alternative to current practice.
Researchers often indicate the clinical significance of their findings by reporting the absolute risk reduction (ARR) and relative risk reduction (discussed in the May 2015 column). The number needed to treat (NNT) is gaining popularity as another measure of clinical significance. The NNT refers to the number of individuals who will need to receive the intervention in order for one individual to experience the positive outcome associated with this intervention. The NNT is the inverse of the ARR: NNT = 1/ARR. You may recall from the May 2015 column that the ARR is calculated by subtracting the rate of the outcome in the intervention group (the experimental event rate, or EER) from the rate of the outcome in the control group (the control event rate, or CER). Thus, NNT = 1/(CER - EER). We always round the NNT up (not down) to the closest whole number, to avoid overstating the effectiveness of the intervention. For instance, an NNT of 4.1 would be reported as 5.
Let us assume that an RCT examines the impact of administering a chlorhexidine gluconate bundle on the risk of developing ventilator-associated pneumonia. The researchers report that the rate of pneumonia among patients who did not receive the bundle (represented by the CER) is 20 per cent and the rate among those who received the bundle (represented by the EER) is five per cent. The NNT is 1/(0.2 - 0.05), which equals 7. The NNT is a measure that can be understood intuitively: the results of our RCT indicate that we would need to treat 100 patients to prevent pneumonia in 15 (remember that 20 out of 100 participants in the control group got pneumonia versus five out of 100 participants in the intervention group), and therefore we would have to treat seven to prevent pneumonia in one.
The smaller the NNT, the more effective the treatment. Determining whether an NNT is clinically significant enough to change practice is a matter of clinical judgment: a small NNT (2 to 5) is typically deemed acceptable for most interventions, but a larger NNT might be acceptable if the treatment prevents a very serious outcome from a common condition, such as cardiovascular disease.
NurseONE.ca resources on this topic
MyiLibrary
Andermann, A. (2012). Evidence for Health: From Patient Choice to Global Policy.
Levin, R. F., & Feldman, H. R. (Eds.). (2005). Teaching Evidence-Based Practice in Nursing: A Guide for Academic and Clinical Settings.
Markle, W. H., Fisher, M. A., & Smego, R. A. (2007). Understanding Global Health.
ProQuest ebrary
D’Cruz, H., Jacobs, S., & Schoo, A. (Eds.). (2009). Knowledge-in-Practice in the Caring Professions: Multidisciplinary Perspectives.
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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