Differences in the number of people able to speak Welsh could be due to several reasons, including changes in the population over time, and changes in people’s ability between censuses.
Gallai gwahaniaethau yn nifer y bobl sy'n siarad Cymraeg fod am nifer o resymau, gan gynnwys newidiadau yn y boblogaeth dros amser, a newidiadau i allu pobl rhwng cyfrifiadau.