Number Needed To Treat - Simple Examples

Simple Examples

There are a number of factors that can affect the NNT. Let's say we have a disease, and a pill to treat the disease, that should work over the course of a week.

  • PA is the probability of still having the disease after taking the pill (i.e. complement of the probability of being cured after taking the pill). The experimental group.
  • PB is the probability of still having the disease even though you didn't take the pill (i.e. complement of the probability of the disease going away by itself). This is the control group, who probably got a placebo pill instead of the real pill.
description PA PB NNT interpretation
Perfect Drug 0.0 1.0 1.0 Everybody is cured with the pill; nobody without
Very Good Drug 0.1 0.9 1.25 Ten take the pill; 8 cured by the pill, 1 cured by itself, 1 still sick.
Satisfactory Drug 0.3 0.7 2.5 Ten take the pill; 4 cured by the pill, 3 cured by itself, 3 still sick.
High Placebo Effect 0.4 0.5 10 Ten take the pill; 6 cured but 5 of those would be cured anyway.
Low Cure Rate 0.8 0.9 10 Ten take the pill, one is cured by the pill, one cured by itself, 8 still have the disease.
Goes Away by Itself 0.1 0.2 10 Ten take the pill and 9 are cured; but 8 would have been cured anyway.
Sabotages Cure 0.9 0.8 -10 Ten take the pill, two would have been cured without it, but with the pill, only one is cured, so really NNH=10.

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