Odds and Evens: A Strategy for Safely Exiting Lockdown 2

Large Controlled Experiment
How could controlled policy experiments be conducted to help inform policies on how to end the current lockdown? One approach would be to alternate between periods of lockdown and removal of restrictions for different groups in the population.

A variety of such cyclic policies have already been tried by several governments in the first wave of the pandemic (see the table below). The idea is that only half the usual population numbers are out mixing at any one time, which reduces the risk of transmitting the virus.

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Summary of some cyclic policies employed during COVID-19 pandemic

·  Colombia — In Bogota, males (females) allowed out on odd (even) days of month.

·  Costa Rica — Nationwide vehicle restrictions, with days permitted according to last digit of license plate.

·  Ecuador — Nationwide, private vehicles allowed to drive on alternate days according to last digit of license plate.

·  Ethiopia — In Addis Ababa, private vehicles allowed on roads on alternate days, according to whether license plate number is odd or even.

·  Honduras — Public allowed essential travel 1 day each week with day determined by last number of ID/passport.

·  India — India adopted several odds and evens policies, e.g.

—Shops with odd and even numbers allowed to open on alternate days.

—In Delhi, stalls in wholesale markets open on alternate days by stall number.

—In Assam, students in even/odd class years attend school on alternate days.

·  Iraq — Vehicles allowed on roads on alternate days, according to whether license plate number is odd or even.

·  Lebanon — Cars allowed on roads on alternate days, according to whether license plate number is odd or even.

·  Panama — Hours allowed out restricted according to last number on ID cards/passports. Additionally, males and females allowed out on alternate days.

·  Paraguay — Nationwide, private vehicles allowed to drive on alternate days according to whether license plate number is odd or even.

·  Singapore — Entry to popular markets allowed on alternate days according to ID card number.

·  U.S.— In several counties in New York state, residents born in odd (even) numbered years could only go out on odd (even) numbered days of month.

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Epidemiological modelling suggests that longer cyclic policies are likely to be more effective. Most people are at their peak infectiousness three to six days after catching the virus. So, with a weekly cyclic policy, if someone contracts COVID-19 during a week they are not locked down, they will probably be most infectious during the following week, when they are locked down.

Unlike an on-again, off-again policy with uncertain timing, a planned cyclic lockdown could provide a way to sustain much of the benefits of social distancing for a longer period. It would also allow a greater and more predictable level of economic activity to continue – for instance, pubs could reopen, but with half the customers. Cyclic policies could also help with the development of an effective test-and-trace system, as there should be fewer cases and less contacts to trace than if lockdown is fully removed.

A cyclic policy could involve two almost identical halves of the population alternating in and out of lockdown on consecutive weeks. A way of implementing such a policy experiment is adopting an odds-and-evens policy based on house number (see figure).

Governments would alternate maintaining and relaxing stay-at-home orders between odd-and-even numbered households.

The effect of the cyclic policy on COVID-19 cases could easily be measured as a person’s address, including their house number, is routinely collected by many healthcare systems. As there should be no other differences between odd and even households, the impact of relaxing the lockdown would become apparent by comparing the pattern of cases in the two groups over time.

Governments could obtain robust evidence from a controlled experiment and then decide if lockdown should continue or be lifted. Just as in a science like physics, where experimental and theoretical research are complementary, government policies need to be based on firm experimental evidence to find the best ways to combat COVID-19 and save lives.

Laurence Roope is Senior Researcher, Health Economics, University of Oxford. Philip Clarke is Professor of Health Economics, University of Oxford. This article is published courtesy of The Conversation.