--  dull sy’n dibynnu ar ddefnyddio data gweinyddol sydd eisoes ar gael o fewn llywodraeth, wedi’i gyfuno gydag arolwg blynyddol gorfodol o bedwar y cant o’r boblogaeth.
--  an approach that depends on the use of the administrative data already held within government, combined with a compulsory annual survey of four per cent of the population.