In order to provide this longer run comparison, the older data were linked onto the post 2004-05 data before indexing onto the 1998-99 database.
Er mwyn creu’r gymhariaeth hon dros gyfnod hwy cafodd y data hŷn eu cysylltu â’r data ar ôl 2004-05 cyn mynegeio ar gronfa ddata 1998-99.