GOV.WALES uses cookies which are essential for the site to work. Non-essential cookies are also used to tailor and improve services. By continuing to use this site, you agree to our use of cookies.
Y gymhareb rhwng amrywiant samplu y sampl cymhleth a sampl syml a ddewiswyd ar hap o'r un maint yw'r 'deff' (design effect - sy'n cyfateb i'r deft wedi ei sgwario).