Modeling the Origin and Possible Control of the Wealth Inequality Surge

The rapid increase of wealth inequality in the past few decades is a most disturbing social and economic issue of our time. In order to control, and even reverse that surge, its origin and underlying mechanisms should be revealed. One of the challenges in studying these mechanisms is to incorporate realistic individual dynamics in the population level in a self-consistent manner. Our theoretical approach meets the challenge by using interacting multi-agent master-equations to model the dynamics of wealth inequality. The model is solved using stochastic multi-agent iterated maps. Taking into account growth rate, return on capital, private savings and economic mobility, we were able to capture the historical dynamics of wealth inequality in the United States during the course of the 20th century. We show that the fraction of capital income in the national income and the fraction of private savings are the critical factors that govern the wealth inequality dynamics. In addition, we found that economic mobility plays a crucial role in wealth accumulation. Notably, we found that the major decrease in private savings since the 1980s could be associated primarily with the recent surge in wealth inequality and if nothing changes in this respect we predict further increase in wealth inequality in the future. However, the 2007–08 financial crisis brought an opportunity to restrain the wealth inequality surge by increasing private savings. If this trend continues, it may lead to prevention, and even reversing, of the ongoing inequality surge.过去数十年来财富不平等的急剧加剧，是我们这个时代最令人不安的社会与经济议题。为了管控甚至扭转这一恶化趋势，我们需要揭示其起源与内在机制。研究此类机制所面临的挑战之一，是能够以自洽的方式将个体的真实动态纳入种群层面的分析。我们的理论方法通过采用交互多智能体主方程（interacting multi-agent master-equations）对财富不平等的动态演化进行建模，以此应对这一挑战。该模型借助随机多智能体迭代映射（stochastic multi-agent iterated maps）完成求解。通过考量经济增长率、资本回报率、私人储蓄占比与经济流动性（economic mobility），我们得以还原20世纪美国财富不平等的历史演化轨迹。研究表明，国民收入中的资本收入占比与私人储蓄占比，是支配财富不平等动态演化的关键因素。此外，我们发现经济流动性对财富积累发挥着至关重要的作用。尤为值得注意的是，我们发现自20世纪80年代以来私人储蓄占比的大幅下滑，主要与近期财富不平等的加剧相关；若在此方面不采取任何改变措施，我们预测未来财富不平等程度还将进一步攀升。然而，2007至2008年的金融危机为我们提供了通过提升私人储蓄占比以遏制财富不平等加剧的契机。倘若这一趋势得以延续，或可预防甚至扭转当前的财富不平等恶化态势。