Research Topics

In a seminal 1972 paper, Robert M. May asked: “Will a Large Complex System Be Stable?” and argued that stability (of a broad class of random linear systems) decreases with increasing complexity, sparking a revolution in our understanding of ecosystem dynamics. Twenty-five years later, May, Levin, and Sugihara translated our understanding of the dynamics of ecological networks to the financial world in a second seminal paper, “Complex Systems: Ecology for Bankers.” Just a year later, the US subprime crisis led to a near worldwide “great recession,” spread by the world financial network. In the present paper we describe highlights in the development of our present understanding of stability and complexity in network systems, in order to better understand the role of networks in both stabilizing and destabilizing economic systems. A brief version of this working paper, focused on the underlying theory, appeared as an invited feature article in the February 2020 Society for Chaos Theory in Psychology and the Life Sciences newsletter (Hastings et al. 2020).

Don’t Forget Finance

Given the economy’s complex behavior and sudden transitions as evidenced in the 2007–08 crisis, agent-based models are widely considered a promising alternative to current macroeconomic practice dominated by DSGE models. Their failure is commonly interpreted as a failure to incorporate heterogeneous interacting agents. This paper explains that complex behavior and sudden transitions also arise from the economy’s financial structure as reflected in its balance sheets, not just from heterogeneous interacting agents. It introduces “flow-of-funds” and “accounting” models, which were preeminent in successful anticipations of the recent crisis. In illustration, a simple balance-sheet model of the economy is developed to demonstrate that nonlinear behavior and sudden transition may arise from the economy’s balance-sheet structure, even without any microfoundations. The paper concludes by discussing one recent example of combining flow-of-funds and agent-based models. This appears a promising avenue for future research.