دانلود رایگان مقاله انگلیسی تحرک و بی ثباتی: افزایش نابرابری درآمد در ایالات متحده - الزویر 2018

abstract

Inequality of family incomes in the United States has increased significantly in the past four decades. This is largely interpreted as a result of unequal mobility, e.g., the rich can get richer at a faster pace than the rest of the population. However, using nationally representative data and the Fokker–Planck equation, our study shows that income mobility in the United States has remained stable. Instead, we find another factor – income volatility, which measures the instability of incomes – has increased considerably and caused the surge of income inequality. In addition, the rising volatility is associated with the plummeting of income-growth opportunity, creating the feeling that the American Dream is in decline. Volatility has often been overlooked in previous studies on inequality, partially because mobility and volatility are usually studied separately. By contrast, the Fokker– Planck equation takes both mobility and volatility into consideration, making it a more comprehensive model.

5. Conclusion

Econophysics is an exciting interdisciplinary research field, but it is not free from criticism, partially because the models and methods from statistical physics are not much acknowledged by mainstream social scientists (including economists, sociologists, and political scientists). In order to bridge this gap, we re-define the terms on the right-hand side of the Fokker– Planck equation (Eq. (2)) as income mobility and volatility, which are critical measures of income dynamics. This equation has two implications. (1) Both mobility and volatility affect income distribution, and their effects, which can be of the same significance, are independent and opposite, i.e., inequality is positively correlated with volatility but negatively with mobility. In this sense, the relationship among mobility, volatility, and inequality resembles the association among drift, diffusion, and temperature described by Einstein’s relation. (2) Mobility and volatility influence income distribution through the aid of the distribution itself (i.e., the gradient of Fp or Sp causes the change in p, not F or S themselves). Thus, the Fokker–Planck equation is far more than a physical model that generates matching cumulative distributions. Instead, each building block of this equation has socioeconomic meaning and can provide illuminating insights into the dynamics of economic inequality. Our analyses show that increasing volatility, rather than mobility, is a major contributor to rising income inequality and the feeling about the fading American Dream in recent decades.