This has meant a slight revision to the percentage of the population aged three or older who can speak Welsh fluently for 2019-20, and some revisions to the data for 2013-15.
Mae hyn yn gyson dros amser ond mae canran y plant a phobl ifanc 3 i 15 oed sy’n gallu siarad Cymraeg wedi bod yn gostwng yn gyffredinol ers dechrau 2019.