Income inequality in the United States continues to increase.

New IRS tax data from Emmanuel Saez, a researcher at U.C. Berkeley who studies income inequality — often collaborating with French economist Thomas Piketty — shows that income inequality between the top 1 percent of income earners and the bottom 99 percent increased again in 2015.

Even though the 1 percent are still doing better than the rest of us, seeing 7.7 percent income growth in 2015, there is a little bit of good news in the data: The bottom 99 percent saw the largest real income growth in 17 years. Average people's incomes rose nearly 4 percent last year.

Writing at the Washington Center for Equitable Growth, Saez explains that there's both good and bad for the 99 percent in the data. In 2015, incomes for the 99 percent grew more than in any year since 1988. This just builds on a trend of high growth over the last three years.

However, between the Great Recession and 2013, 99 percent incomes barely moved at all. So even though incomes have been growing a lot recently, most people still haven't dug themselves out of the crater caused by the recession.

The 1 percent don't have that problem, and they continue to march ahead.