Table 2.

Grade-specific information about school children and the study sample

School grades	Total children in 13 schools, n	Size of selected classes,† 1st class + 2nd class = total	Examined children, n	Consent rate in 1st class (%)
6th	3831	484 + 475 = 959	556	360/484 (74.3)
7th	3323	438 + 446 = 884	554	323/438 (73.7)
8th	2769	419 + 408 = 827	560	324/419 (77.3)
9th	2964	384 + 358 = 742	568	321/384 (83.5)
Total	12,887	1,725 + 1,687 = 3,412	2,238	1328/1725 (77.0)

^†Attendance rate was above 95% in each school.