To differing extents, technology, trade, diminished union power and changes in industrial structure are all thought to have played roles in the increase in income inequality over the last 25 years. Changes in these factors alter the earnings opportunities available to workers, imposing constraints upon workers' earnings. But not all causes of increasing income inequality are related to market constraints.
Research suggests that choices made by workers are just as important.
Since single parent families earn less than two parent families, income inequality is closely connected to individuals' choices to marry, divorce and have children. Between 1970 and 1995, the share of families with children under 18 headed by two parents fell from 87 to 69 percent, while the share of families with children headed by single parents rose from 13 to 31 percent. Over the same period, Robert Lerman of the Urban Institute estimates that these changes in family structure can account for almost half the increase in income inequality between 1971 and 1989. A second important choice factor is the number of hours individuals work. Professor Chinhui Juhn of the University of Houston points to the increased number of hours worked by wives of high income males.