Randomisation was started on April 4 , 2007 , and was stopped on April 15 , 2013 , when a data and safety monitoring board appointed by the National Institute of Neurological Disorders and Stroke of the National Institutes of Health recommended halting randomisation because of superiority of the medical management group ( log-rank Z statistic of 410 , exceeding the prespecified stopping boundary value of 287 ) .