Florence Jaumotte and Carolina Osorio Buitron pen this article for International Monetary Fund's March Finance and Development volume.
The decline in unionization in recent decades has fed the rise in incomes at the top
Inequality has risen in many advanced economies since the 1980s, largely because of the concentration of incomes at the top of the distribution. Measures of inequality have increased substantially, but the most striking development is the large and continuous increase in the share of total income garnered by the 10 percent of the population that earns the most—which is only partially captured by the more traditional measure of inequality, the Gini coefficient (see Chart 1).
The Gini is a summary statistic that gauges the average difference in income between any two individuals from the income distribution.
Read the full report here: http://www.imf.org/external/pubs/ft/fandd/2015/03/jaumotte.htm