[Using "number needed to treat" to interpret treatment effect]

Evidence-based medicine (EBM) has rapidly emerged as a new paradigm in medicine worldwide. The clinical medicine in twenty-first century could be the era of EBM. Randomized controlled trial has been regarded as the gold standard for evaluating the treatment effect of a new drug or a new therapy. The effect of a treatment versus controls may be expressed in relative or absolute measures. Relative measures include relative risk, relative risk reduction, and odds ratio. Absolute risk reduction and number needed to treat are absolute measures. For rational decision-making, absolute measures are more meaningful because they have taken baseline risk and the amount of clinical benefit into account. The number needed to treat (NNT), the reciprocal of the absolute risk reduction, is a useful estimate of treatment effect. Interpreting a NNT should be very cautious accompanied by information about the experimental treatment (including drugs and surgical procedures), the control treatment for comparison, the baseline risk of the study population, the length of the follow-up period, and an exact definition of the endpoint.