WASHINGTON (AP) — A Federal Reserve survey shows that despite an ultra-low 3.9 percent unemployment rate, about one-third of U.S. adults faced financial insecurity last year and often struggled to pay unexpected expenses.

For three in 10 adults, their monthly incomes fluctuated — often because their work schedules changed at short notice — and that caused about one in ten Americans to miss some bill payments. Forty percent of adults would have had to borrow money or sell something to pay an emergency expense of just $400.

At the same time, the survey finds the improving economy is benefiting more Americans, including at all education and income levels. Nearly three-quarters of U.S. adults say they are either living comfortably or doing OK financially, up from 71 percent in 2016.