From mid-2019 this percentage decreased most months, reaching a low point in December 2019, before increasing in early 2020, prior to the COVID-19 pandemic.
O ganol 2019 ymlaen, roedd y ganran hon wedi gostwng y rhan fwyaf o fisoedd, gan gyrraedd y pwynt isaf ym mis Rhagfyr 2019, cyn dechrau cynyddu ym misoedd cynnar 2020 cyn pandemig COVID-19.