The Survey of Personal Incomes (SPI) is a set of income tax data, produced annually by HMRC from the information it holds on a large sample group of UK individuals.
Mae’r Arolwg o Incwm Personol (SPI) yn set o ddata treth incwm, a gynhyrchir bob blwyddyn gan CThEF o’r wybodaeth sydd ganddo am grŵp sampl mawr o unigolion yn y DU.