From 2014 there has been some divergence in estimates for 16 to 18 year olds which has widened further in the last few years.
Ar gyfer pobl ifanc 16 i 18 oed, cynyddodd y gyfran ychydig rhwng 2008 a 2012, ac mae wedi amrywio ar tua 89-90% yn ystod y blynyddoedd diwethaf.