[1] Harvard Univ, Sch Publ Hlth, Dept Hlth Policy & Management, Boston, MA 02115 USA
[2] Massachusetts Gen Hosp, Dept Surg, Boston, MA 02114 USA
[3] Brigham & Womens Hosp, Dept Surg, Ctr Surg & Publ Hlth, Boston, MA 02115 USA
[4] WHO, Patient Safety Programme, CH-1211 Geneva, Switzerland