Just how dramatic the changes have been can be seen from Figure 1 . As recently as 1960, nearly three-quarters of all households were married couple families, but by 1996 that share had fallen below 54 percent. Most of the decline in the share of married couple families was counterbalanced by the rapid growth in non-family households during this period, whose share doubled to 30 percent. As this discussion illustrates, understanding the somewhat arcane distinction between households and families as defined by the Census Bureau, is central to Samuelson's argument. Households consist of single individuals living alone, and people living in the same housing unit, whether or not they are related.
Families consist of people living together who are related by marriage or birth.
In 1996, there were 30 million fewer families than households. Our focus, therefore, is on Census data for families, and changes between 1979 and 1996. It does mean that the average real standard of living of families has increased much more during the intervening 17 years than officially reported. For example, the increased share of single-head families between 1979 and 1996 depressed family income by nearly 10 percent, because this family type had average income 60 percent less than married couple families in 1996. By 1996, only one-quarter of married couple families had just one working spouse.