The educational level of American adults is on the rise as more college graduates go on to earn master’s, professional and doctoral degrees.

Since 2000, the number of people age 25 and over whose highest degree was a master’s has doubled to 21 million. The number of doctoral degree holders has more than doubled to 4.5 million.

Now, about 13.1 percent of U.S. adults have an advanced degree, up from 8.6 percent in 2000.