We examine the mobility of individuals in the United States based on equiva
lent family income-that is, total income of all family members adjusted for
family size according to the equivalence scale implicit in the U.S. povert
y line. Our analysis, which tracks movements across quintiles, centers on f
our questions: How much movement is there across the family income distribu
tion? How has this mobility changed over time? To what extent are the movem
ents attributable to factors related to changes in family composition versu
s events in the labor markets? In light of major socioeconomic changes occu
rring in the quarter-century under study, have the determinants of mobility
changed over time? Our findings indicate that mobility rates in the 1980s
differed little from those in the 1970s. However individuals in families he
aded by a young person or a person without a college education were less li
kely to experience upward mobility in the 1980s than in the 1970s.