Changes in living arrangements and the age structure of the population have drastically changed the allocation of Income among various groups of Americans. These changes include, among others, passage of the baby boom generation through the life cycle, increases in life expectancy, postponement of marriage, increases in divorce and separation, and the entry of women into the work force.

This Brief shows how demographic, social, and economic changes over the past two decades have altered the share of the market held by various demographic groups. "Market share" is defined as the aggregate income of a particular demographic group as a proportion of the aggregate income of all households. These data were obtained by means of the March 1970 and March 1990 Current Population Surveys. Household income figures are for the previous calendar year and are in 1989 dollars.