More Americans are struggling to pay for housing, even as the economy improves and unemployment falls, according to a new summary of the housing market published Wednesday.

More than one-third of U.S. households, or 39.8 million people, paid enough for housing — more than 30 percent of their incomes — in 2014 to be deemed officially cost “burdened,” the analysis published by the Harvard Joint Center on Housing Studies found. And 16.5 percent of households were “severely burdened,” meaning that they paid half their income on housing.