The gap had previously been relatively stable at around 14.7 percentage points between 2015/16 and 2018/19 before widening in the most recent 2 years.
Cyn hynny roedd y bwlch wedi bod yn gymharol sefydlog ar tua 14.7 pwynt canran rhwng 2015/16 a 2018/19 cyn ehangu yn ystod y 2 flynedd ddiweddaraf.