This variation is both in terms of the relationship of the proxy to the subject (parents were much better than spouses or children) and also by the level and type of qualifications held.
Mae’r amrywiad hwn yn nhermau perthynas y dirprwy â’r gwrthrych (roedd rhieni’n llawer gwell na gŵyr/gwragedd priod neu blant) a hefyd yn nhermau’r lefel a math o gymhwyster oedd gan bobl.