There was an increase to a peak from 2018 to 2019, a downward trend in 2020 and 2021, followed by an upward trend in 2022 and 2023.
Cafwyd cynnydd i uchafbwynt rhwng 2018 a 2019, tuedd ar i lawr yn 2020 a 2021, ac yna tuedd ar i fyny yn 2022 a 2023.