Derivation of Number Needed to Treat for Benefit Over Entire Range of Functional Disability

Background and Purpose—The SAINT I trial demonstrated that the neuroprotective agent NXY-059 improves the distribution of acute stroke patient outcomes on the modified Rankin Scale (mRS) of global disability. Standard dichotomized number-needed-to-treat (NNT) analyses for the magnitude of treatment benefit range widely, from 22.7 to infinity, and each capture only a portion of the observed beneficial shift in outcomes. Derivation of an NNT value reflecting the treatment’s benefit over the entire range of the mRS is required to describe the clinical import of the trial results. Methods—The minimum and maximum possible NNTs for benefit over the range of mRS global disability outcomes were calculated by completing a joint distribution outcome table for a model population of 1000 patients, shifting responders by the greatest and smallest possible increments, respectively. The biologically most plausible NNT within this range was derived by having 10 neurologist and emergency-physician acute stroke–care experts independently specify the joint distribution of outcomes in model samples of 1000 patients assigned to placebo and active therapy. Results—The minimum possible NNT for benefit incorporating all mRS state transitions is 7.9 and the maximum is 16.7. The biologically most plausible NNT for 1 additional patient to have a better outcome by 1 or more grades on the mRS outcomes is 9.8 (95% CI, 8.7 to 10.9). Conclusions—Considering improvements in global disability over the entire outcome range, the SAINT I trial results indicate that for every 100 patients treated, 10 will benefit and none be harmed as a result of treatment. (Stroke. 2007; 38:1515-1518.)