Number needed to harm should be measured for treatments

EDITOR—The concept of number needed to treat was an attempt to introduce both simplicity and objectivity into the evaluation of treatment. It is helpful both on a large scale when treatments are compared and care is commissioned and on the personal level when doctor and patient choose the management for the individual. The number needed to treat gives a comparison of treatments and outcomes that both doctors and patients should understand.

One problem of this unimodal numerical scale for measuring the likely outcome of a treatment is that it …