Quantifying clinical relevance.

Communicating clinical trial results should include measures of effect size in order to quantify the clinical relevance of the results. P-values are not informative regarding the size of treatment effects. Cohen's d and its variants are often used but are not easy to understand in terms of applicability to day-to-day clinical practice. Number needed to treat and number needed to harm can provide additional information about effect size that clinicians may find useful in clinical decision making, and although number needed to treat and number needed to harm are limited to dichotomous outcomes, it is recommended that they be considered for inclusion when describing clinical trial results. Examples are given using the fictional antipsychotic medications miracledone and fantastapine for the treatment of acute schizophrenia.