The survey is based on the World Health Organization’s cross-national Health Behaviour of School-aged Children (HBSC) survey, in which Wales has taken part since 1985.
Daw data’r rhaglen o’r NCCHD, sy’n cynnwys cofnodion dienw ar gyfer yr holl blant a anwyd yng Nghymru, sy’n byw yng Nghymru neu sydd wedi’u trin yng Nghymru ac a anwyd ar ôl 1987.