In order to test the new two-adult interviewing process, additional random numbers for each address in a quota were added to the table.
Cesglir data'n barhaus drwy gydol pob blwyddyn arolwg i adlewyrchu patrymau teithio tymhorol, gyda chriw newydd o ymatebwyr yn cael eu gwahodd i gymryd rhan bob wythnos.