New York (CNN Business) Income inequality in the United States worsened in 2019. Earners at the top of the income ladder received the largest increase in their paychecks, according to a report from the Economic Policy Institute.

Wages at the 95th percentile grew by 4.5% last year, while the median increase was just 1%.

That's nothing new : The median hourly wage climbed about 15% between 1979 and 2019, but pay for workers in the 95th percentile grew more than 63% over the past 40 years.

"Wage growth for low- and middle-wage workers continues to be slower than would be expected in an economy with relatively low unemployment," said EPI Senior Economist Elise Gould.

Economists have struggled to explain the sluggish wage growth for average and low earners. America's labor market is healthy and the unemployment rate sits near a 50-year low. The Bureau of Labor Statistics' latest jobs report showed the American labor force participation ticked up in January to its highest level since 2013

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