There has been a notable fall in this measure, with an initial sharp drop at the start of the year, followed by a steady fall over the whole of 2020 to 2021.
Bu gostyngiad nodedig yn y mesur hwn, gyda gostyngiad cychwynnol sydyn ar ddechrau'r flwyddyn, ac yna gostyngiad cyson trwy gydol 2020 hyd 2021.