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The mission of Our World in Data is to make data and research on the world’s largest problems understandable and accessible.
While most of our work focuses on large problems that humanity has faced for a long time – such as child mortality, natural disasters, poverty and almost 100 other problems (see here) – this article focuses on a new, emerging global problem: the ongoing outbreak of the coronavirus disease [COVID-19].
The outbreak started in China in late 2019 and by March 2020 the disease has spread to countries around the world.
This article covers a developing situation and the Our World in Data team is regularly updating it: The last update was made on March 13, 2020 (21:00 London time).
About this page
Limitations of current research and limitations of our presentation of current research
The purpose of this article on COVID-19 is to aggregate existing research, bring together the relevant data and allow readers to make sense of the published data and early research on the coronavirus outbreak.
Most of our work focuses on established problems, for which we can refer to well-established research and data. COVID-19 is different. All data and research on the virus is preliminary; researchers are rapidly learning more about a new and evolving problem. It is certain that the research we present here will be revised in the future. But based on our mission we feel it is our role to present clearly what the current research and data tells us about this emerging problem and especially to provide an understanding of what can and cannot be said based on this available knowledge.
As always in our work, one important strategy of dealing with this problem is to always link to the underlying original research and data so that everyone can understand how this data was produced and how we arrive at the statements we make. But scrutiny of all reported research and data is very much required. We welcome your feedback. In the current situation we read and consider all feedback, but can not promise to reply to all.
Our World in Data relies on data from the World Health Organization
In this document and the associated charts we report and visualize the data from the ‘Situation Reports’, which the World Health Organization (WHO) publishes daily. The WHO reports this data for each single day and they can be found here at the WHO’s site.
According to the WHO the data published in these reports is correct as of 10am (CET; Geneva time) each time.
We – the Our World in Data team – went back through all the daily Situation Reports and found several minor errors in WHO’s data. We immediately notified the WHO and are in close contact with the WHO’s team to correct the errors that we pointed out to them. We document all errors we found.
We should emphasize that while there are errors in the published WHO data, all of these errors are minor and do not affect our or the public’s understanding of the evolving COVID-19 outbreak in a significant way. As can be seen in our documentation these errors should be corrected (and will be), but they are small.
Here is our detailed documentation of where the WHO’s data is sourced from and how we corrected its data – we also provide several options to download all corrected data there.
Not only the World Health Organization publishes COVID-19 data
A number of other organizations – including Johns Hopkins University and other research teams – publish their own lists of the number of confirmed cases and deaths. Johns Hopkins also publishes data on ‘recovered cases’ while the WHO does not.
At the end of this page we link to their visualizations and list links to other data sources.
Cases of COVID-19
The number of total cases is what we want to know, but their number is not known
To understand the scale of the COVID-19 outbreak, and respond appropriately, we would want to know how many people are infected by COVID-19. We want to know the total number ofcases.
However, the total number of COVID-19 cases is not known. It is unknown by us at Our World in Data, or any other research, governmental or reporting institution.
There are several reasons why the total number is not known.
Whilst for some the symptoms are very severe (see below here), for a large share of the population the symptoms are mild. In such cases people may be unaware that they are infected with COVID-19, and therefore not get seen, and diagnosed, by a doctor.1,2
The second reason that the confirmed cases are only a fraction of the total number is that many countries are struggling to test a large number of cases. Not every person that should be tested is able to. Since testing is crucial, we looked into this in more detail. Because of large problems with data availability on the scale of testing, we did a manual review of data on COVID-19 testing across national reports, and collated the most recent estimates that we could find as of 13 March 2020, 19.00 GMT. You find our work on this here.
Confirmed cases is what we do know
What we do know is the number of confirmed cases. The World Health Organization (WHO) explains that a confirmed case is “a person with laboratory confirmation of COVID-19 infection, irrespective of clinical signs and symptoms.”3
The WHO also speaks of ‘suspected cases’ and ‘probable cases’, but the WHO Situation Reports do not provide figures on ‘probable cases’, and only report ‘suspected cases’ for Chinese provinces (‘suspected cases’ by country is not available).4
The daily Situation Reports list the number of confirmed cases; we rely on these reported numbers for the regular updates of our own datasets presented below.
As explained, the number of confirmed cases is lower than the number of total cases because not everyone is tested.
Growth of cases: How long did it take for the number of confirmed cases to double?
In the section below we present the latest data on the number of confirmed cases by country, and how this has changed over time.
But in an outbreak of an infectious disease it is important to not only focus on the number of cases, but also the growth rate at which the number of cases is increasing.
The growth rate is an essential metric to understand and to monitor.
This is because a fast growth rate can lead to very large numbers rapidly, even if the current numbers of cases and deaths are small when compared with other diseases.
A helpful metric to measure the rate of change is to look at each country and ask: How long did it take for the number of confirmed cases to double?
Let’s take an example: if the number of confirmed cases as of today is 1000, and there were only 500 cases three days ago then we would say that it took three days for the number of confirmed cases to double.5
The doubling time of cases has changed and it will change in the future. It would be wrong to extrapolate current growth into the future.
But it is important to keep focusing on the doubling time. As long as cases are doubling at a constant rate thegrowth is exponential. We humans tend to think in linear growth processes even when the growth is exponential, as psychological research has shown for decades. Below we give some intuition about exponential growth and provide the referenced psychological research on this.
Understanding exponential growth
The time it takes for the number of cases to double will change during the outbreak and it would be wrong to make projections based on the assumption that this stays constant. But it is important to remind ourselves of the nature of exponential growth.
If during an outbreak the number of cases is in fact doubling and this doubling time stays constant, then the outbreak is spreading exponentially.
Under exponential growth 500 cases grow to more than 1 million cases after 11 doubling times.6 And after 10 more doubling times it would be 1 billion cases.
This is in no way a prediction for the number of cases we should expect; it is simply a reminder that exponential growth leads to very large numbers very quickly, even when starting from a low base. And it is important to be reminded of the nature of exponential growth because most of us do not grasp exponential growth intuitively. Psychologists find that humans tend to think in linear growth processes (1, 2, 3, 4) even when this is not appropriately describing the reality in front of our eyes. This bias – to “linearize exponential functions when assessing them intuitively” – is referred to as ‘exponential growth bias’.7
Psychological research shows that “neither special instructions about the nature of exponential growth nor daily experience with growth processes” improved the failure to grasp exponential growth processes.8
The global average hides more than it reveals: why we show this data country by country
It is important to not only look at the global number of cases and deaths. Some countries – like China and Korea – have very substantial counter measures in place and new daily confirmed cases have declined.
Many other countries do not have comparable measures in place and, as the table shows, numbers are rising fast. The global average does not allow us to understand this.
The global average hides the differences between countries that are successfully reducing the number of confirmed cases and those that fail to achieve this – and this is what is most important in this early phase of the COVID-19 epidemic, as we explain in detail below.
Growth: Country by country view
As just explained, it is crucial to not just look at the number of cases, but also their growth over time. For this reason the following table answers the following question for all countries: How long did it take for the number of confirmed cases to double?
You can sort the table by any of the columns by clicking on the column header.
Data: The data shown here is published by the World Health Organization (WHO). Here is our documentation of the data and an option to download all data.
The figures shown are based on WHO data up to and including 13th March 2020.