Due to small sample sizes, when looking at sub-groups it has been necessary to use estimates based on the average of 3 periods and therefore should be used to compare groups or regions only.
Gan fod y samplau’n fach, wrth edrych ar is-grwpiau bu’n rhaid defnyddio amcangyfrifon yn seiliedig ar gyfartaledd y 3 chyfnod ac felly dylid eu defnyddio i gymharu grwpiau neu ranbarthau’n unig.