Founded in 1964, the Palestine Liberation Organization (PLO) is an umbrella organization for groups that represent the Palestinian people before international states. The Palestinian National Authority, officially established in 1994 as a result of the Oslo Accords, is an interim administrative body nominally responsible for governance in Palestinian population centers in the West Bank and Gaza Strip. Since 1978, the United Nations has observed an annual International Day of Solidarity with the Palestinian People. According to Perry Anderson, it is estimated that half of the population in the Palestinian territories are refugees and that they have collectively suffered approximately US$300 billion in property losses due to Israeli confiscations, at 2008–09 prices.