Fig. 1: Kaplan–Meier curves for event-free survival with and without carotid endarterectomy. The curves show the probability of avoiding an ipsilateral stroke of any degree of severity (left-hand panels) and a disabling or fatal ipsilateral stroke (right-hand panels) among patients with carotid stenosis of at least 70% (top panels) or 50% to 69% (bottom panels) who were randomly assigned to undergo carotid endarterectomy (surgical group) or to receive medical therapy alone (medical group). Also shown are the p values from the Mantel–Haenstzel χ² test used to compare the survival curves, with the 95% confidence interval for each curve and the overlap between the confidence intervals indicated by bands of color. The numbers along the horizontal axis are the numbers of patients in each group who were still at risk during each year of follow-up. Reproduced with permission from Barnett HJM, Taylor DW, Eliasziw M, Fox AJ, Ferguson GG, Haynes RB, et al, for the North American Symptomatic Carotid Endarterectomy Trial Collaborators. Benefit of carotid endarterectomy in symptomatic patients with moderate and severe stenosis. N Engl J Med 1998;339:1415-25. Copyright © 1998 Massachusetts Medical Society. All rights reserved.