Although each rate is available for the two population bases, as well as for several other age groups, there is an official standard population base used for each of the rates, as follows:
Er bod pob cyfradd ar gael ar gyfer y ddwy sail poblogaeth, yn ogystal ag ar gyfer sawl grŵp oedran arall, defnyddir sail poblogaeth safonol swyddogol ar gyfer pob un o’r cyfraddau, fel a ganlyn: