[1] Tehran University of Medical Sciences,Department of Epidemiology and Biostatistics
[2] I.R.Iran,undefined
[3] University of London,undefined
[4] Medical Statistics Unit,undefined
[5] London School of Hygeine and Tropical Medicine,undefined
[6] University of London,undefined
[7] Cancer and Public Health Unit,undefined
[8] London School of Hygiene and Tropical Medicine,undefined
[9] University of London,undefined