Korea’s middle class has steadily decreased from 74.47 percent of the population in 1990 to 67.33 percent in 2010, while the percentages of high-income and low-income earners have increased 2.23 and 4.9 percentage points, respectively, to 20.43 percent and 12.24 percent over the last 20 years, according to a report released by the Korea Institute for Health and Social Affairs Monday.