According to a study by the National Community Reinvestment Coalition, D.C. has experienced more "intense" gentrification than any other American city, with 40% of neighborhoods gentrified. Approximately 17% of Washington, D.C. residents were age 18 or younger as of 2010, lower than the U.S. average of 24%. However, at 34 years old, the district had the lowest median age compared to the 50 states as of 2010. , there were an estimated 81,734 immigrants living in Washington, D.C. Major sources of immigration include El Salvador, Vietnam, and Ethiopia, with a concentration of Salvadorans in the Mount Pleasant neighborhood. As of 2010, there were 4,822 same-sex couples in the city, about 2% of total households, according to Williams Institute. Legislation authorizing same-sex marriage passed in 2009, and the district began issuing marriage licenses to same-sex couples in March 2010. Approximately a third of Washington, D.C. residents were functionally illiterate as of 2007 compared to a national rate of about one in five. The city's relatively high illiteracy rate is attributed in part to immigrants who are not proficient in English. , 85% of D.C. residents age5 and older spoke English at home as a primary language. Half of residents had at least a four-year college degree in 2006. In 2017, the median household income in D.C. was $77,649; also in 2017, D.C. residents had a personal income per capita of $50,832 (higher than any of the 50 states). However, 19% of residents were below the poverty level in 2005, higher than any state except Mississippi. In 2019, the poverty rate stood at 14.7%. , more than 90% of Washington, D.C. residents had health insurance coverage, the second-highest rate in the nation. This is due in part to city programs that help provide insurance to low-income individuals who do not qualify for other types of coverage. A 2009 report found that at least three percent of Washington, D.C. residents have HIV or AIDS, which the Centers for Disease Control and Prevention (CDC) characterizes as a "generalized and severe" epidemic. Of the district's population, 17% are Baptist, 13% are Catholic, 6% are evangelical Protestant, 4% are Methodist, 3% are Episcopalian or Anglican, 3% are Jewish, 2% are Eastern Orthodox, 1% are Pentecostal, 1% are Buddhist, 1% are Adventist, 1% are Lutheran, 1% are Muslim, 1% are Presbyterian, 1% are Mormon, and 1% are Hindu. The city is populated with many religious buildings, including