the primary source of capital for the ultra-wealthy. Retired people also have little income, but may have a high net worth, because of money saved over time. Additionally, income does not capture the extent of wealth inequality. Wealth is most commonly obtained over time, through the steady investing of income, and the growth of assets. The income of one year does not typically encompass the accumulation over a lifetime. Income statistics cover too narrow a time span for it to be an adequate indicator of financial inequality. For example, the Gini coefficient for wealth inequality increased from 0.80 in 1983 to 0.84 in 1989. In the same year, 1989, the Gini coefficient for income was only 0.52. The Gini coefficient is an economic tool on a scale from 0 to 1 that measures the level of inequality. 1 signifies perfect inequality and 0 represents perfect equality. From this data, it is evident that in 1989 there was a discrepancy in the level of economic disparity; the extent of wealth inequality was significantly higher than income inequality. Recent research shows that many households, in particular, those headed by young parents (younger than 35), minorities, and individuals with low educational attainment, display very little accumulation. Many have no financial assets and their total net worth is also low. According to the Congressional Budget Office, between 1979 and 2007, incomes of the top 1% of Americans grew by an average of 275%. (Note: The IRS insists that comparisons of adjusted gross income pre-1987 and post-1987 are complicated by large changes in the definition of AGI, which led to households within the top income quintile reporting more of their income on their individual income tax form's AGI, rather than reporting their business income in separate corporate tax returns, or not reporting certain non-taxable income in their AGI at all, such as municipal bond income. In addition, IRS studies consistently show that a majority of households in the top income quintile have moved to a lower quintile within one decade. There are even more changes to households in the top 1%. Without including those data here, a reader is likely to assume households in the top 1% are almost the same from year to year.) In 2009, people in the top 1% of taxpayers made $343,927 or more. According to US economist Joseph Stiglitz the richest 1% of Americans gained 93% of the additional income