[1] Columbia Univ, Dept Epidemiol, Mailman Sch Publ Hlth, New York, NY USA
[2] Univ San Carlos, Fac Ciencias Med, Guatemala City, Guatemala
[3] Tulane Univ, Sch Publ Hlth & Trop Med, New Orleans, LA USA
[4] Univ Chile, Fac Med, Sch Publ Hlth, Santiago, Chile
[5] Harvard Med Sch, Dept Hlth Care Policy, 180 Longwood Ave, Boston, MA 02115 USA