[ 4 ] See ' Mixing modes within a social survey: opportunities and constraints for the National Survey for Wales ', section 3.2.3 for a fuller review.
[ 4 ] (Gweler ' Cymysgu dulliau mewn arolwg cymdeithasol: cyfleoedd a chyfyngiadau ar gyfer Arolwg Cenedlaethol Cymru ', adran 3.2.3 i gael adolygiad mwy cyflawn)