The Growth incidence curve from 1988 to 2008, also known as the Elephant Graph, shows the income growth by percentile of global income distribution. It shows two things: global inequality has declined and the middle class (80th and 90th percentile of global income) stagnated.
Lower income groups made large increases in income due to globalization (manufacturing shifted to cheaper labor and exports). The top income group benefited from an expansive global market (more people could be their customer) and advantages accrue to the leader. Middle income groups benefited from cheaper consumption, but other goods became more expensive—housing, education, and health care.
- How people get rich and income inequality argues that the income growth of the top percentile is mostly fine