Reply to the Comments by Prof. Yomoyuki Kawada

[4] . It is extremely difficult to obtain large cohorts prospectively, especially based on susceptibility-weighted imaging, which is relatively new and has so far not been regularly performed in routine clinical practice [5] . Thus, as we have previously discussed [2] , we may emphasize here again that due to the limited sample size, the conclusion that there is a relationship between intraventricular hemorrhage and cerebral microbleeds should be regarded with caution and is not suggested to be used as the basis for clinical practice without further confirmatory studies. We are grateful to Prof. Tomoyuki Kawada for these statistical comments [1] . He suggested that there was no detailed description of the variable selection in the Cox proportional hazards regression model and the insufficient sample size precluded our study from constructing stable multivariable regression models to arrive at solid conclusions. In the Cox proportional hazards regression model of our study, the confounder profile for subsequent intraventricular hemorrhage in moyamoya disease was selected from risk factors which had previously been reported or considered rational. They were simultaneously included for multivariate analysis. However, due to the limited events during the 23-month follow-up, it indeed could not reach the threshold of 10 events for each variable. It has been recognized as the major limitation of our study, which was fully addressed in the Discussion section on p. 474 [2] . We are totally aware that the optimal way to keep the statistical validity in multivariate analysis is to create a larger cohort [3] . However, as this is an uncommon disease, the incidence of moyamoya disease ranges from 0.02 to 0.41 per 100,000 people in Asia Received: August 10, 2013 Accepted: August 12, 2013 Published online: October 30, 2013