Over the longer term, the rate has decreased by 2.4 percentage points over the last five years and by 4.7 percentage points over the last decade.
Dros y tymor hirach, mae’r gyfradd wedi gostwng 2.4 pwynt canran dros y pum mlynedd diwethaf a 4.7 pwynt canran dros y degawd diwethaf.