“Number needed to treat”: A tool for summarizing treatment effect, and its application in anaesthesia and pain management

Number needed to treat (NNT) has become an increasingly used method of reporting study outcomes. It incorporates baseline risk as well as relative risk reduction to provide a whole number that indicates the effort which must be expended to obtain one additional beneficial outcome. Variations of NNT have been developed to account for harmful effects of treatment, and to improve the clinical utility of NNT. NNT provides clinicians with a means of comparing efficacy of different treatments which is more clinically useful and can help guide the provision and distribution of health resources. However, NNT has the potential to mislead the clinician if its limitations are not appreciated. NNT has been increasingly used in the reporting of outcomes from trials and systematic reviews in anaesthesia, pain management, and clinical medicine.