COVID-19: numbers badly in need of context

I did not plan to write this post, but I feel the urge to do so. I bet that many lives could be saved and much suffering could be avoided if decision-makers would be more aware of the fact that the numbers of the COVID-19 pandemic are badly in need of context.

We’re witnessing an unprecedented case in recent history, one to which no-one was really prepared. Although, notably, we were at least aware of the fact that it would have been bad, once it arrived. See for example this interesting TED talk by Bill Gates, back in 2015:

Now that the next outbreak is here, let’s try to understand something about the numbers that are constantly and incessantly thrown around us, without any context.

In epidemics, 1 is not equal to 1

Imagine I told you that in country X, there have been 24 new cases of COVID-19 infection. Would it be good or bad news?

Imagine then that I told you that in country Y, one case of COVID-19 has been detected today. Again, good or bad?

The key thing to understand is that, once again, these numbers by themselves do not mean anything.

If country X is China, then news of 24 new infections is great.

If country Y is Nigeria, one new case is a potential disaster.

Everything depends on the context. China, for example, had thousands of new cases per day just a few weeks ago, so the fact that the new cases are in such a reduced number means that their containment measures are working effectively.

In the case of Nigeria, a single case of COVID-19 could mean that the disease spreads in a country with a fragile healthcare system, and with one of the most crowded metropolitan areas of the world. Just one case, not twenty, not one hundred, could mean that the disease infects thousands of people and spread very rapidly.

Numbers carry a history

To someone that has been working with numbers all their life, this is obvious, but – alas – it is not at all obvious to someone that does not have that background.

The most striking demonstration of this fact that I’ve come across for COVID-19 is summarized in the following graph.

“Most western countries are on the same coronavirus trajectory. Hong Kong and Singapore have managed to slow the spread”

John Burn-Murdoch, The Financial Times

Here, coronavirus trajectory precisely refers to the context: in mathematical terms, it is the growth rate. In human terms, it’s the history that the numbers carry with them. The fact that some countries (the ones that have not taken drastic containment measures yet) are on that same trajectory means that we can be fairly certain that that trend will continue along that dashed line in the graph. If you take Singapore, instead, you see that the growth of the numbers looks radically different. Strict quarantine and rigorous measures to prevent the spread are reflected in that very different history (growth rate).

Now let’s look at this graph from another perspective, the one of decision-makers. Unfortunately, most of western countries have decided not to take serious action against the COVID-19 spread because they are waiting for the situation to be really bad, like in Italy. However, if you look at this graph, you can actually predict, with a lot of painful accuracy, when the situation will be really bad. And if the decision-makers understood what this meant, they would act boldly right away, without waiting for the situation to get worse.

Understanding this is key to prevent a disastrous spread of the COVID-19 infection, and unless drastic measures are taken rapidly, all countries that are on that same trajectory will end up like Italy, with thousands of new cases every day.

When to act?

Now. Independently on whether in your country, region, or city, the number of infected people is 100, 500, or 1000. We need to take serious action from now. Not tomorrow, not in one week. That is because we know the context of those numbers: the context means that the epidemic is spreading, and it will continue to spread unless we stop it. And stopping will requires extraordinary action and everyone’s sacrifice.

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