Bootstrap statistics of ECASS II data: Just another post hoc analysis of a negative stroke trial?

The results of the Second European-Australasian Acute Stroke Study (ECASS II) were negative with respect to the primary endpoint. This post hoc analysis of ECASS II data was designed to make the least number of a priori assumptions. This is accomplished by a bootstrap-based hypothesis test on a non-parametric test statistic. No assumptions are made on shape or variance of population distributions and the method does not suffer from the disadvantages of dichotomization. By reducing the number of a priori assumptions, the possibilities to modify the test result by adjusting the test procedure are minimized. Results: If rt-PA does not improve the outcome (null hypothesis), the probability of observing a difference of modified ranking scale equal or larger than the one observed in ECASS II is 0.047. We therefore rejected the null hypothesis. Copyright (C) 2001 S. Karger AG, Basel.