Updated March 21st
I’ve been producing my own charts to understand the Johns Hopkins coronavirus data. Here’s the situation on March 21st.
Here’s all the countries with 100+ reported deaths. I have zoomed in on the first 4 weeks since the 10th death.
This linear scale obscures what’s happening. We need to switch to a logarithmic scale to get a better view.
How to think about exponentials
If you have a human brain you may find exponentials counterintuitive. I’ll try to explain but I’m also unfortunately limited to a human brain so bear with me.
With the log scale, each step up is 10 times bigger than the last.
These next two charts both show the same data for the equation y=m^x. So if m=2, on day 4 you have 2⁴ = 16 cases.
The log scale helps you see the growth rate. When m is 1, there’s no growth. When m is 2, the total doubles every day.
So when you are looking at log-scale charts, the main thing to pay attention to is the gradient of the line.
Steep line = rapid growth. Flat line = no growth.
Let’s zoom out and see a longterm view of the growth rates of reported deaths.
It’s 8 weeks since the 10th death in Wuhan (Hubei province) and they’re down to m=1.003, with 3139 reported total deaths.
In the last week UK has m=1.45. Another week at that rate and the total death toll jump from 234 yesterday to 3,154 by Saturday (234⨉1.45⁷).
See how important it is to get the growth rate down quickly!
Okay what about confirmed cases? Let’s take a look:
It’s important to understand that every country has a different strategy for testing and reporting, so you can’t understand the whole picture just by looking at these charts. For a more comprehensive picture, check out this excellent work from Our World In Data.
Even with that proviso, it is easy to see the trends emerging: many countries are following in step with China and Italy, a few have it under control, and the rest are too early to know.
Another reference point that may be useful: here in Italy, we went from 100 to 10,000 cases in about 16 days. From my own experience of living through that exponential expansion: at 100 cases I thought “this is no big deal”, too small to feature on my list of daily priorities. By 10,000 cases, the country had to go into lockdown, because hospitals are overloaded and doctors have to choose who lives and who dies.
Exponential doesn’t mean “very fast” it means “imperceptibly gradual at first, and then it is suddenly overwhelming”.
So please stay safe, look after your family, friends, neighbours, and remember, I am not a specialist I am just a dude in Italy with an overactive spreadsheet.
p.s. join me on Twitter for latest updates.
p.p.s. there’s a tutorial here if you want to make your own charts.