Data are inconclusive as to the impacts that reliefs, discounts, and exemptions are having on taxpayer behaviour, as well as the extent to which they are appropriate and necessary.
Nid oedd y data yn ddiamheuol ynghylch yr effeithiau mae rhyddhadau, disgownt ac esemptiadau yn eu cael ar ymddygiad trethdalwyr, nac ynghylch y graddau maent yn briodol ac angenrheidiol.