No data was collected in 2020 due to the COVID-19 pandemic response, and 2021 and 2022 data was strongly affected by it.
Nid oes datganiad ystadegol llawn wedi'i gyhoeddi ar gyfer 2019-20 oherwydd bod adnoddau dadansoddol yn blaenoriaethu'r ymateb i bandemig COVID-19.