Why lockdown? Simplified arithmetic tools for decision-makers, health professionals, journalists and the general public to explore containment options for the novel coronavirus

Gerry Killeen; Samson Kiware

Here we introduce a simplified arithmetic modelling tool for predicting COVID-19 transmission dynamics and how it is likely to respond to different containment, delay or mitigation strategies. We coin the term arithmetic modelling, as distinct from the ubiquitously used term mathematical modelling, to convey the fact that it uses only addition, subtraction, multiplication, division, rounding off, a few conditional statements (eg. if, less than/greater than, and/or), and two unavoidable power terms, to make the necessary calculations. This tool includes no differential equations, calculus, limits, distributions, stochastic simulations or agent-based approaches that would render it opaque to most non-specialist readers, such as medical and public health practitioners, decision-makers, journalists and the general public. The model is presented in userfriendly Excel® and Shiny® formats that allow non-specialists to explore, query, critique and understand the containment decisions facing their country and the world at large. For those who wish to satisfy themselves that the calculations make intuitive sense, the Excel® version provides a complementary spreadsheet format in which the formula for each cell can be critically examined. For those content to accept the underlying arithmetic, the Shiny® format provides a convenient interactive web application that can be used on any device. While a formal mathematical description of this model has been critically reviewed by specialist experts, it is provided only as an online supplement because none of the principles, assumptions or predictions are entirely new, and because in our experience nothing deters non-specialists from reading an article faster than equations do.