From "Efficacy versus Effectiveness of Carotid Endarterectomy" Effective Clinical Practice, January/February 1999. 1:30-36.
Figure 2. The number of carotid endarterectomy procedures needed to prevent one major stroke or death in patients with severe asymptomatic stenosis, moderate symptomatic stenosis, and severe symptomatic stenosis. Efficacy is calculated from trial data; effectiveness accounts for the higher surgical mortality rates likely to be encountered in clinical practice.>