Comments on number-needed-to-treat derived from ordinal scales

A well-known effect size measure in evidence-based medicine is the number-needed-to-treat (NNT) in order to get one more responder or one more patient with improvement. It is defined as the reciprocal of the simple risk difference of the two groups being compared (test group with innovation product and control group). The NNT effect size measure has been largely accepted in the scientific c…