aDepartments of Anesthesiology and Epidemiology, Columbia University Vagelos College of Physicians and Surgeons and Mailman School of Public Health, New York, New York

bDepartments of Neurology and Psychiatry, Harvard Medical School

cDepartments of Neurology and Psychiatry, Boston Children's Hospital

dDepartment of Environmental Health, Harvard T.H. Can School of Public Health, Boston, Massachusetts, USA

Correspondence to Caleb Ing, MD, MS, Associate Professor of Anesthesiology (in Epidemiology), Departments of Anesthesiology and Epidemiology, Columbia University Vagelos College of Physicians and Surgeons and Mailman School of Public Health, New York, 622W. 168th Street, BHN 4-440, New York, NY 10032, USA. Tel: +1 212 305 2413; e-mail: [email protected]