Note [u2]: The data item for those aged 17 and 20 is based on between 25 and 39 responses and is categorised as being of limited quality.
Nodyn [u2]: Mae'r eitem ddata ar gyfer y rhai 16 i 18 oed sy’n anabl yn seiliedig ar rhwng 25 a 39 ymateb ac wedi'i dosbarthu fel ei bod o ansawdd cyfyngedig.