Number needed to treat: A primer for neurointerventionalists

Background: The number needed to treat is a commonly used statistical term in modern neurointerventional practice. It represents the number of patients that need to be treated for one patient to benefit from an intervention. Given its growing popularity in reflecting study results, understanding the basics behind this statistic is of practical value to the neurointerventionalist. Methods: Here, we review the basic theory and calculation of the number needed to treat, its application to stroke interventions, and its limitations. In addition, we demonstrate several simple methods of calculating the number needed to treat utilizing recent thrombectomy trial results. By presenting the number needed to treat as a universal metric, we provide a comprehensive comparative of the number needed to treat for key stroke therapies, including mechanical thrombectomy, tissue plasminogen activator, carotid endarterectomy, and prevention with antiplatelet and statin drugs. Conclusions: In comparison with available stroke therapies, mechanical thrombectomy stands out as the most effective acute intervention in patients with emergent large-vessel occlusions. Understanding how the number needed to treat is derived and its implications helps provide perspective to clinical trial data, identify health-care resource priorities, and improve communication with patients, health-care providers, and additional key stakeholders.