Working Paper Article Version 2 This version is not peer-reviewed

# Are Models Useful? Reflections on Simple Epidemic Projection Models and the Covid-19 Pandemic

Version 1 : Received: 10 June 2020 / Approved: 12 June 2020 / Online: 12 June 2020 (10:10:59 CEST)
Version 2 : Received: 4 July 2020 / Approved: 7 July 2020 / Online: 7 July 2020 (08:51:10 CEST)

How to cite: Artzrouni, M. Are Models Useful? Reflections on Simple Epidemic Projection Models and the Covid-19 Pandemic. Preprints 2020, 2020060148 Artzrouni, M. Are Models Useful? Reflections on Simple Epidemic Projection Models and the Covid-19 Pandemic. Preprints 2020, 2020060148

## Abstract

In this paper we provide an expository overview" of classic epidemic projection models. Starting with the simple case of an epidemic that grows exponentially we then investigate compartmental" models. These assume that the growth of an infected population is limited endogenously by the size of the underlying pool of susceptibles. We then describe a new family of so-called "Exo-r" statistical models, which hinge on an exogenously driven growth rate of the infected population. This family, which can be used to model both infections and deaths, captures parsimoniously both the depletion of susceptibles and the effect of interventions such as lockdowns and social distancing". The model is used to fit numbers of Covid-19 infections in China. It is also used to model and project deaths in the United States. Results are used to inform a discussion on i) the challenges at hand and ii) the extent to which epidemic projection models may be useful despite being wrong.

## Supplementary and Associated Material

http://bit.ly/3bAYFZr: Supplementary material related to Exo-r model

## Subject Areas

epidemic model; covid

Comment 1
Commenter: Marc Artzrouni
Commenter's Conflict of Interests: Author
Comment: minor typos, corrections for final accepted version
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