inequality in total wealth, with the top 1% of the population owning 42.7%, the next 19% of Americans owning 50.3%, and the bottom 80% owning 7%. However, after the Great Recession which started in 2007, the share of total wealth owned by the top 1% of the population grew from 34.6% to 37.1%, and that owned by the top 20% of Americans grew from 85% to 87.7%. The Great Recession also caused a drop of 36.1% in median household wealth but a drop of only 11.1% for the top 1%, further widening the gap between the 1% and the 99%. Dan Ariely and Michael Norton show in a study (2011) that US citizens across the political spectrum significantly underestimate the current US wealth inequality and would prefer a more egalitarian distribution of wealth, raising questions about ideological disputes over issues like taxation and welfare. Wealth concentration Wealth concentration is a process by which created wealth, under some conditions, can become concentrated by individuals or entities. Those who hold wealth have the means to invest in newly created sources and structures of wealth, or to otherwise leverage the accumulation of wealth, and are thus the beneficiaries of even greater wealth. Economic conditions The first necessary condition for the phenomenon of wealth concentration to occur is an unequal initial distribution of wealth. The distribution of wealth throughout the population is often closely approximated by a Pareto distribution, with tails which decay as a power-law in wealth. (See also: Distribution of wealth and Economic inequality). According to PolitiFact and others, the 400 wealthiest Americans had "more wealth than half of all Americans combined." Inherited wealth may help explain why many Americans who have become rich may have had a "substantial head start". In September 2012, according to the Institute for Policy Studies, "over 60 percent" of the Forbes richest 400 Americans "grew up in substantial privilege". The second condition is that a small initial inequality must, over time, widen into a larger inequality. This is an example of positive feedback in an economic system. A team from Jagiellonian University produced statistical model economies showing that wealth condensation can occur whether or not total wealth is growing (if it is not, this implies that the poor could become poorer). Joseph E. Fargione, Clarence Lehman and Stephen Polasky demonstrated in 2011 that chance alone, combined with the deterministic effects of compounding returns, can lead to