CASES is a mathematical model of dynamic relationships among industrial sectors of several major economic regions within the state of California, and simulate the impact of an unmitigated outbreak of COVID-19 on the health and employment of the employed labour force at the beginning of March, 2020. Those impacts are estimated by coupling the dynamic economic model to a SIR (Susceptible, Infected, Recovered) epidemiological model, parameterized with real disease and demographic data. CASES addresses a counterfactual situation in which California did not implement an economic shutdown in 2020, but instead weathered the first wave of the pandemic with an open economy.
The model assumes that the number of employed workers in a sector is a function of sufficient supply of necessary materials or services to the sector, and the demand for its products and services. Those supplies and demands are thus also functions of employment levels in all sectors. The inter-dependencies are described with a set of coupled ordinary differential equations. If a model SES is isolated from variations of external input and output variables, such as external subsidies and consumer demand, the system will reach an equilibrium in which employment within sectors remains constant. Our approach is thus to isolate an SES in this manner, and to then introduce a perturbation representing the loss of workers to COVID-19 infection, specifically disabling disease or death. The system of ODEs then measures, over time, the cascading consequences of the outbreak as workers are lost to infection, or jobs are lost because of the impact on inter-sector supply and demand. Such cascades are well recognized and unavoidable consequences of both networked systems (the inter-industry network) and their internal feedback processes (e.g. the partial regulation of sector activity by the activities of other sectors). The timing, frequency and magnitude of a cascade are often hard or impossible to predict in complex systems on the basis of input data alone, and forecasting can only be done with the analysis or simulation of models that capture the salient features of such systems.
CASES is coded in Julia, and the code should work for Julia version >=1.0. Scripts are provided for simulation of ten different California systems, including: San Francisco-San Mateo-Redwood City MD (metropolitan division), Oakland-Berkeley-Livermore MD, San Jose-Sunnyvale-Santa Clara MSA (metropolitan statistical area), Stockton-Lodi MSA, Fresno MSA, Los Angeles-Long Beach-Glendale MD, Anaheim-Santa Ana-Irvine MD, Riverside-San Bernardino-Ontario MSA, Oxnard-Thousand Oaks-Ventura MSA, and San Diego-Carlsbad MSA. Required datasets are also provided.
