## Externalities, Expectations, and Epidemiology

OK, we are going to hit the ground running with some basic theory and background material. Marginal Revolution University has two short videos on what “externalities” are and how we can use this concept to think about contagion.

Next up, the IGM experts panel from the University of Chicago polls superstar economists on issues of the day. Notice what question is being asked and whether economists tend to agree or not. Also out of the University of Chicago we have a short piece by Michael Greenstone. Take a peek at what questions his colleagues are looking into. Is there anything there that interests you?

From there, we move to some epidemiological concepts. Scott Page walks us through a simple derivation of R_{0}, the Basic Reproduction Number you’ve undoubtedly been hearing about. What are the key parameters of these models? Are they exogenous or endogenous? Why does that matter? Once we have seen that, the 495 students should read the Gonclaves piece and 295 can choose between Gonclaves and Yates, flattening the curve and all that. There is also a handout that contains some basic definitions, and I will quiz you to make sure you know what these mean.

Finally, * I highly recommend* the short piece on herd immunity (you should be able to calculate the percentage of the population that needs to be immune using R

_{0}). I have also included the comprehensive, controversial, and wildly variable IMHE projections for your perusal.

**Economics: Theory & Data**

- “Intro to Externalities,” Marginal Revolution University
- “External Benefits,” Marginal Revolution University

- Policy for the COVID-19 Crisis, IGM Forum
- Michael Greenstone, “Key Economic Facts About COVID-19,” Becker-Friedman Institute, March 31, 2020

**Basic Epidemiology and R _{0}**

- Short video introducing R
_{0 } - Scott E. Page, “Contagion Models 1: Diffusion,” Model Thinking*
- Scott E. Page, “Contagion Models 2: SIS Model,” Model Thinking

- Basic definitions from Imperial College and elsewhere
- Bruno Goncalves, “Epidemic Modeling 101: Or why your CoVid-19 exponential fits are all wrong,” (light mathematics)
- Christian Yates, “How to Model a Pandemic,”
*The Conversation*, March 25, 2020 - Short piece on R
_{0}and herd immunity

**Some Basic Arithmetic**

- Compound growth and the Rule of 70 (it’s actually the Rule of 72, but whatevs)
- Natural logs in economics

**Materials for the Week**