Fig. 1: The trend of income quantile of 286 cities at the prefecture level and above in China in 2000, 2010, and 2018.

Note: ① The data on per capita disposable income of urban residents from 2000 to 2018 was derived from the China Urban Statistical Yearbook from 2001 to 2019. ② The decile curve corresponds to the main vertical axis (left), indicating that the income levels of all prefecture-level and above cities in 2000, 2010, and 2018 are divided into 10 equal deciles, forming a trend of the change in income quantiles over time. This trend is shown for the years 2000, 2010, and 2018. From the gradual rise of the three decile curves in 2000, 2010, and 2018, it can be seen that the income level at each percentile has increased. This indicates that residents’ income has generally increased over time. However, the curve has also gradually steepened, which suggests that in the same year, the difference between the income levels of higher and lower-income individuals has increased. This means that the income gap has widened. ③ The quartile curve corresponds to the secondary vertical axis (right) and represents the difference in income levels between 2018 and 2000 at each subpoint. The slope of the quartile spread curve is positive. In 2018, compared to 2000, the difference in income levels for the lower quartile was smaller, while the difference in income levels for the higher quartile was larger. This resulted in an increased degree of dispersion in the income gap, leading to an expansion of the income gap.