From May 2020 onwards telephone interviews were carried out with a random sample of people who had previously taken part in a full-year, face-to-face National Survey.
O fis Mai 2020 ymlaen, cynhaliwyd cyfweliadau dros y ffôn gyda hapsampl o bobl a oedd wedi cymryd rhan mewn Arolwg Cenedlaethol blwyddyn lawn, wyneb yn wyneb.