TO THE EDITOR

Abstract

Division of Neurosurgery, University of Toronto, Toronto, Canada Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada Acknowledgment date: March 20, 2012. Acceptance date: June 19, 2012. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.