Under the ie system, only a minority of households included three generations at a time because nonsuccessor sons (those who were not heirs) often set up their own household. From 1970 to 1983, the proportion of three-generation households fell from 19% to 15% of all households, while two generation households consisting of a couple and their unmarried children increased only slightly, from 41% to 42% of all households. The greatest change has been the increase in couple-only households and in elderly single-person households.