By Josh Boak, AP Economics Writer

WASHINGTON (AP) — Financial inequality became even wider in the United States last year, with average income for the top 1 percent of households surging 7.7 percent to $1.36 million.

Income for the richest sliver rose twice as fast as it did for the remaining 99 percent of households, according to an updated analysis of tax data by Emmanuel Saez, an economics professor at the University of California, Berkeley.

Still, the incomes of households outside the top 1 percent appear finally to be recovering from the Great Recession, which officially ended seven years ago. After accounting for inflation, their average income rose 3.9 percent last year to $48,768 — the strongest annual gain since 1998. Contrast that with the period from 2008 to 2011, when the economy remained in a rut and inflation-adjusted income for the bottom 99 percent of households was falling.

"It is indeed the best growth year for the bottom 90 percent and bottom 99 percent since the late 1990s," Saez said. "At the same time, top incomes grow even faster, leading to a further widening of inequality, which continues an alarming trend."

Income inequality has been a rallying cry of the 2016 election, with more Americans turning fearful and angry about a shrinking middle class. Donald Trump has pledged to restore prosperity by ripping up trade deals and using tariffs to return manufacturing jobs from overseas. Hillary Clinton has backed a debt-free college option and higher minimum wages to help the middle class.

Much of the debate has been fueled by research conducted over the years by Saez and his collaborator Thomas Piketty.

The IRS data reviewed by Saez shows that income growth last year was greatest among the super-wealthy — the top 0.1 percent of households. Their incomes climbed nearly 9 percent to an average of $6.75 million.

The tax data helps capture income inequality more fully than government surveys, which often fail to include the tiny fraction of ultra-rich Americans who play professional sports, star in Hollywood blockbusters, manage global corporations or trade successfully in the financial markets.

To Learn More:

U.S. Top One Percent of Income Earners Hit New High in 2015 amid Strong Economic Growth (by Emmanuel Saez, Washington Center for Equitable Growth)

U.S. Leads Developed World…in Income Inequality (by Noel Brinkerhoff and David Wallechinsky, AllGov)

Income Inequality in U.S. Reaches Record High (by Noel Brinkerhoff, AllGov)