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Background and Purpose-Recruitment rate is a major determinant of the duration, cost, and feasibility of acute stroke trials. Methods-We performed a meta-analysis of all randomized, controlled trials of Ն300 subjects that were designed to evaluate the efficacy of a medical intervention for the treatment of acute ischemic stroke. Data about trial recruitment, organization, and inclusion/exclusion criteria were abstracted independently by 2 reviewers who applied predefined criteria. Recruitment efficiency was defined as the number of subjects enrolled per study center per month of recruitment. Results-Of 32 trials meeting inclusion criteria, the average recruitment efficiency was 0.79 subjects per center per month (range 0.08 to 3.7). Recruitment efficiency did not vary by geographic region (Pϭ0.36), but trials conducted in 1 country had more efficient recruitment than international studies (Pϭ0.03), and recruitment efficiency declined with each percentage increase in the total number of study centers (Pϭ0.002). The primary study entry criteria that predicted reduced recruitment efficiency were the maximum allowable time from stroke to study enrollment (Pϭ0.002) and the exclusion of mild strokes (Pϭ0.009). Trials with a treatment window Ͼ6 hours had approximately double the recruitment rates of trials that used treatment windows Յ6 hours (1.03 versus 0.52 patients per center per month). Conclusion-Recruitment rates for acute stroke trials are influenced by organizational structure and study entry criteria.Characterizing predictors of recruitment may help optimize future trial design. (Stroke. 2006;37:123-128.)

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