On the other hand, an NNT of 1 might be seen when treating a sensitive bacterial infection with antibiotics, whilst an NNT of 40+ might still be beneficial in other situations where the clinical endpoint is severe, such as using aspirin to prevent a heart attack. For example, an NNT of between 2 and 5 would normally indicate an effective therapy, such as a pain killer for acute pain. However, the value of an NNT should be interpreted in light of the clinical context. In theory, the higher the NNT, the less effective the treatment, because more people need to receive the treatment for one person to benefit. The ideal NNT would be 1, where all the patients in the treatment group have benefitted, but no one has in the control arm. There are also methods available for deriving NNT using odds ratios and relative risk reduction. Insert Equation re Number needed to treat
#5E HEALTH CALCULATOR TRIAL#
The number needed to treat from this trial is calculated as follows: The following 2×2 contingency table was obtained in a randomised controlled trial: The worked example below is taken from the examiners’ comments from the June 2001 sitting of the MFPH Part A Examination. Insert Equation re Number needed to treat here: Insert Equation re Absolute Risk Reduction here: The NNT is the reciprocal of the absolute risk reduction – the difference between the proportion (or rate) of events in the active treatment intervention group (Pa), and the proportion (or rate) of events in the control group (Pc): 2 Similar measures are reported in vaccination and screening studies (number needed to vaccinate/screen) and their values are derived in a similar fashion to the NNT. It provides an attractive means of summarising the results of a clinical trial in a single figure, because the meaning of a sentence such as ‘20 patients need to be treated to avoid one additional death over a five-year period’ is easily understood by both doctors and patients. We are currently in the process of updating this chapter and we appreciate your patience whilst this is being completed.įirst described in 1988 1, the number needed to treat (NNT) can be thought of as the number of patients that need to be treated in order for one to benefit.
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