1. a Department of Biostatistics and Injury Prevention Research Center , University of North Carolina at Chapel Hill , USA
2. b Department of Behavioral Sciences and Department of Clinical Epidemiology , University of the Philippines , Manila, Philippines
3. c Department of Social Medicine , University of North Carolina at Chapel Hill , Manila, USA
4. d Escola Paulista de Medicina , Universidade Federal de São Paulo , Manila, Brazil
5. e Injury Prevention Research Center , University of North Carolina at Chapel Hill , Manila, USA
6. f Department of Biostatistics , University of North Carolina at Chapel Hill , Manila, USA