If you are committed to the idea that poor families need to work to earn a living, this has been a great three decades. For households in the bottom 20 percent of earnings in the United States — in 2012, that meant less than $14,687 a year — the share of income from wages, benefits and tax credits has risen from 57.5 percent of their total income in 1979 to 69.7 percent in 2010.

The percentage of their income from public benefits, including Medicaid, food stamps, Social Security and unemployment insurance, has fallen in that time.

The fact that more of poor families’ income is coming from wages doesn’t necessarily mean that they’re getting paid more, though. In fact, based on the E.P.I.'s analysis of data from the Census Bureau, it appears that what income gains they are seeing are coming from working more hours, not from higher hourly pay.

Indeed, if you adjust for the higher number of hours worked, over the 1979 to 2007 period (selected to avoid the effects of the steep recession that began in 2008), hourly pay for the bottom 20 percent of households rose only 3.2 percent. Total, not per year. In other words, in nearly three decades, these lower-income workers saw no meaningful gain in what they were paid for an hour of labor. Their overall inflation-adjusted income rose a bit, but mainly because they put in more hours of work.

The researchers at E.P.I. also looked at demographic factors that contribute to poverty, including race, education levels and changes in family structure (such as the number of one-parent versus two-parent households). This look at the data also shows rising inequality as the biggest factor in contributing to the poverty rate, dwarfing those other shifts.

Debates over what kind of social welfare system the United States ought to have are always polarizing, from the creation of the Great Society in the 1960s to the Clinton welfare reforms of the 1990s to the Paul Ryan budgets of this era. Conservatives tend to attribute the persistence of poverty, even amid economic growth, to the perverse incentives that a welfare state creates against working.