However, in some of the education systems where the PISA standards were not met, such adjustments may be less effective and some results may therefore be somewhat higher than they might otherwise be.
Fodd bynnag, yn rhai o'r systemau addysg lle na fodlonwyd safonau PISA, gall addasiadau o'r fath fod yn llai effeithiol ac felly gall rhai canlyniadau fod ychydig yn uwch nag y byddent fel arall.