The fall in household size and the rise of the primary individual in the United States.

The long-term fall in household size in the United States is discussed within the framework of the aging of the population, continuing as the effects of fertility and mortality decline accumulate. Using distributions of households by size from U.S. census data 1790-1970 and a components of change analysis on primary individuals for 1950-1974, household changes are related to demographic change for the periods 1790-1900, 1900-1950, and 1950-1974. Fertility and mortality declines have unambiguous impact on household size until the increases in primary individuals begin. But these, too, have a theoretically interesting, if indirect relationship to population structure.