Subsamples are chosen carefully so that groups of related subsampled questions are asked of the same respondents, to allow cross-analysis between those related questions.
Dewisir yr is-samplau yn ofalus fel bod grwpiau o gwestiynau cysylltiedig gael eu gofyn i'r un ymatebwyr, er mwyn medru croes-ddadansoddi rhwng y cwestiynau hynny.