May 13, 2020 16:48:08
Coronavirus cases are still soaring around the world. These charts will help you understand what is going on.
Statistics are central to the coronavirus story. Every day, we hear new numbers of cases and deaths, but what do they actually mean?
Firstly, it’s vitally important to understand what data we have and its limitations.
The main thing we know for certain is that the numbers we’re seeing are incomplete. That doesn’t mean the information they provide isn’t useful, but you need to keep this at the front of your mind when you’re looking at the number of coronavirus cases.
We’re going to be looking at the data in a few different ways total confirmed cases, deaths, and testing rates so you can understand why each metric is useful and how they can all tell one part of the COVID-19 story.
We’ll then step through a few things we can learn from the data so far.
The data in this story is updated daily. Check back to track the outbreak over time.
Confirmed cases (Linear scale)
- The US outbreak is at a different scale to other countries
- Europe remains a major centre for outbreak
- Russia now has the second largest number of confirmed cases
The confirmed number of coronavirus cases is the baseline for most of the charts you’ve been seeing. It shows how many cases have been registered in a country over time. This is a linear chart, which is good for quickly seeing the scale of the outbreak in different countries.
As you can see, the United States and Europe have the largest overall outbreaks, and there are clear differences in how well countries have dealt with it.
What this chart doesn’t give a good indication of is how quickly the virus is spreading in countries that are at different stages of the outbreak.
The sheer size of the US outbreak means it’s hard to see how other countries like Australia are doing.
A better way to do that is to use a logarithmic chart, which is good for tracking exponential growth, and so allows us to compare countries with different-sized outbreaks.
Confirmed cases (log scale)
- Australia’s growth rate has slowed considerably
- Despite a later start, the UK is on a trajectory to have an outbreak as large as Italy and Spain
- The rate of growth in the US outbreak is slowing
To make it easier to compare countries, this chart starts from the moment each country passed 100 cases, which aligns their outbreaks.
That lets us compare the shape of each country’s outbreak: the more vertical the line at any point in time, the faster the virus is spreading. When countries get their outbreaks under control, the line flattens off.
As you can see, the number of confirmed cases provides a good snapshot of the outbreak across countries, but it is heavily dependent on how many tests a country is doing: if you don’t test for coronavirus, you can’t find it.
If you need an explanation about exponential growth or log charts, we’ve got you covered at the bottom of this article. And don’t worry, you’ll be able to tap straight back.
Deaths (log scale)
This is a grim but effective way to look at the outbreak. Tracking the number of COVID-19 deaths is one way to provide a clearer idea of what’s actually going on in situations where testing is much lower.
In a country like Germany, the low death rate is likely to indicate that they’ve got a better handle on how many cases are in the country overall.
But these figures are still incomplete, as shown by an analysis of the number of “excess deaths” in the UK, (and comprehensively detailed by the Financial Times) which suggests coronavirus may have caused more than double the official death toll.
As with cases, the log chart is best for comparing the rate of deaths across countries, but when it comes to raw numbers there are stark differences visible.
Deaths (linear scale)
- Without an expansive testing regime, it’s possible to miss many cases
- The number of positive tests per total tests provides an indication of whether countries might be missing cases
Testing is an important part of understanding how the virus is spreading, and the data we have available. There are two particularly important metrics to watch: how many tests a country is doing, and how many of those tests are coming back positive.
Because countries are reporting testing in different ways, and at different times, it is hard to compare across borders. But here are cumulative tests for Australia, the United States, South Korea and the United Kingdom, compiled by Our World in Data – which has been tracking the COVID-19 spread.
From this, you could say the US is doing a great job, and it certainly has increased testing to high levels. But let’s look back at the month of March, when the virus was rapidly spreading around the world.
To put that period in context, PM Scott Morrison announced our lockdown on March 22 after ramping up restrictions over a week.
So, March was a crucial month to be finding out how the virus was spreading in the community.
For much of March, the US and the UK were barely doing any tests compared to South Korea.
And while we don’t have national statistics for Australia for all of March, by the time we collated them, they were at a higher rate than the UK.
It is also important to look at how many tests are being done on a daily basis.
While the US has rapidly increased the amount of testing it is able to do, we need to keep an eye on how the number of tests compares to the number of cases being found.
We know in countries with large outbreaks testing isn’t capturing every person who catches COVID-19, and this means changes in the rate of testing can have a big impact on a country’s numbers.
What looks like a spike in cases may be the result of them doing more tests, but also if the amount of tests levels off then that may hide an increase in cases.
So you can see that just focusing on how many tests a country does has its limits. This is where looking at how many tests a country does for every positive diagnosis is useful.
For this chart a higher number is better. It means a country is having to test more people to find positive cases, suggesting they are missing fewer cases in the community.
A large proportion of tests in the US and UK are still coming back positive, indicating compared to Australia there are much higher numbers of undiagnosed cases in these countries.
Why haven’t we taken into account population?
On the surface, it doesn’t make much sense for us to compare huge countries like China or the US with small countries like Taiwan or Australia so why aren’t we looking at cases per capita?
If we were examining an illness that were not transmissible, like cancer perhaps, or a virus that were already prevalent in the population, then per capita statistics would be useful.
But what we’re trying to show is the size of the outbreak in each country and, importantly, how quickly it’s growing.
And because these viruses (if left unchecked) grow exponentially, they can spread through a population incredibly quickly. This is relevant when the only measures we really have to combat its spread are at a national/state level (e.g. close borders, test people, and get everyone to socially isolate).
In terms of its population, the size of China’s outbreak is tiny (0.006 per cent of the population), but it essentially closed down a country of more than 1 billion people to get it under control.
Cases per capita also makes it look like a country like Taiwan, which has a similar population to Australia and 440 cases, hasn’t been that much more effective than China in controlling the virus.
And even if you do take into account population, the largest outbreaks in Europe and the United States still have far higher rates of cases and deaths than countries like Australia.
Cases by population (Linear scale)
What can we learn from the data so far?
These are some of the countries to watch
- Outside of Europe and the US, Brazil and Russia have among the highest cases in the world and their numbers are still growing quickly.
- India and Mexico also have significant outbreaks that are growing.
Acting early, quarantines, and testing work but secondary outbreaks remain a risk
- Singapore, Taiwan, South Korea and Vietnam all benefitted from acting early and aggressive testing and contact tracing.
- However, Singapore has seen a subsequent rise in cases, largely driven by outbreaks in migrant worker camps, which is evidence that just because you get the virus under control initially it doesn’t mean it will stay that way.
Social distancing can shut the virus down quickly, if you get in early enough
- The UK, Australia and New Zealand all implemented aggressive social distancing policies within days of each other.
- However, by that stage the UK already had a much larger outbreak and therefore its social distancing measures have not been able to shut down the spread as quickly or effectively.
Autocrats aren’t necessarily better at dealing with coronavirus
- The autocratic nature of the Chinese Government meant measures to detect a pandemic weren’t effective and the virus was allowed to spread initially.
- Iran has had one of the worst outbreaks, and there is evidence the death toll is much higher than is being reported.
- Denmark and New Zealand are social democracies, and have been successful in slowing the spread of the virus.
- Both Taiwan and Vietnam have been incredibly effective at stopping the virus, but despite their different types of government have followed the same plan of aggressive isolation, testing and tracing.
How to better understand the charts
Exponential growth is a pattern viruses tend to initially follow, due to the way they’re spread. So a good way to to measure the spread of coronavirus is to look at how long it takes for the number of cases in a country to double.
Initially, the differences between the virus doubling over a few days or a week might look small.
But as time passes, the differences increase dramatically.
By week three, the differences are stark and remember this example started from just one case. Not to mention, the coronavirus pandemic is predicted to run for months.
It’s for this reason that early intervention can have a huge impact. One single infection in the early days of the outbreak can easily scale into hundreds, perhaps even thousands, over time.
What is a logarithmic chart
To better compare countries with lots of cases and those with only a few, it’s useful to use a logarithmic scale on the vertical axis of charts tracking the number of coronavirus cases.
This means that instead of rising in a linear fashion (1, 2, 3 etc), it is scaled by powers of 10 (10, 100, 1,000 etc). This is a particularly useful way to view coronavirus cases because the virus initially tends to spread exponentially rather than in a linear fashion.
It can be a little hard to wrap your head around. But here’s another way to think about it. If a country’s cases are growing exponentially, it’ll appear on this chart as a straight line headed up and to the right.
And the angle of the line indicates just how fast it’s growing.
Stay up-to-date on the coronavirus outbreak
About the data
- Australian case numbers are sourced from federal, state and territory health department media releases and press conferences and compiled by ABC News. For countries other than Australia, the number of cases comes from data compiled by Johns Hopkins University.
- The testing snapshot figures are taken from Our World in Data.
- Health authorities update their figures at different times of day, so the numbers shown do not reflect the same point in time in each jurisdiction.
- It’s important to note that data in this story represents confirmed cases and deaths, which includes presumptive positive cases actually identified by authorities. The actual number of cases and deaths in each country is likely to be higher, as an unknown proportion of people with the virus would not have been tested. Therefore, the numbers’ accuracy will also vary depending on how much testing each country is doing.
May 13, 2020 05:13:54
Contact Tim Leslie