The study, by Peter Cunningham, a senior fellow at the CSHSC, found that from 2001 to 2006 the number of families below the federal poverty level (FPL) and with private insurance who faced high-burden health costs increased 17 percent. (The 2010 FPL for a family of four is $22,050.) However, the number of middle-class and high-income families facing such a challenge increased by 56 percent and 98 percent, respectively. Among the 11 million people with private insurance whose health care costs rose above 10 percent of their gross income in those six years, 39 percent were in high-income families and 48 percent were in middle-income families. Although the FPL is adjusted annually for inflation, at the current FPL, the study defined low-income households as families of four with combined pre-tax earnings of from $22,050 to $44,100; middle-income families as those earning from $44,101 to $88,200; and high-income families as those earning more than $88,200.