Covid vaccine mandates as deadline looms.

Coronavirus (COVID-19) Testing

Research and data: Hannah Ritchie, Edouard Mathieu, Lucas Rodés-Guirao, Cameron Appel, Charlie Giattino, Esteban Ortiz-Ospina, Joe Hasell, Bobbie MacDonald, Diana Beltekian, Saloni Dattani and Max Roser
Web development: Lars Yencken, Daniel Bachler, Ernst van Woerden, Daniel Gavrilov, Marcel Gerber, Matthieu Bergel, and Jason Crawford

We are grateful to everyone whose editorial review and expert feedback on this work helps us to continuously improve our work on the pandemic. Thank you. Here you find the acknowledgements.
Why is data on testing important?
No country knows the total number of people infected with COVID-19. All we know is the infection status of those who have been tested. All those who have a lab-confirmed infection are counted as confirmed cases.

This means that the counts of confirmed cases depend on how much a country actually tests. Without testing there is no data.

Testing is our window onto the pandemic and how it is spreading. Without data on who is infected by the virus we have no way of understanding the pandemic. Without this data we cannot know which countries are doing well, and which are just underreporting cases and deaths.

To interpret any data on confirmed cases we need to know how much testing for COVID-19 each country actually does.

The Our World in Data COVID-19 Testing dataset
Because testing is so very crucial to understanding the spread of the pandemic and responding appropriately we have focused our efforts on building a global dataset on COVID-19 testing.

The testing dataset is updated around twice a week. The latest version is always available in the section below.
And as with all our work, it is freely accessible for everyone. The data can be downloaded here on GitHub.

The positive rate: A crucial metric for understanding the pandemic

Here we show the share of tests returning a positive result – known as the positive rate.

This metric offers us two key insights: firstly as a measure of how adequately countries are testing; and secondly to help us understand the spread of the virus, in conjunction with data on confirmed cases.

The positive rate is a good metric for how adequately countries are testing because it indicates the level of testing relative to the size of the outbreak. To be able to properly monitor and control the spread of the virus, countries with more widespread outbreaks need to do more testing.

According to criteria published by WHO in May 2020, a positive rate of less than 5% is one indicator that the epidemic is under control in a country.1

Because limited testing makes it likely that many cases will be missed, the positive rate can also help our understanding of the spread of the virus. In countries with a high positive rate, the number of confirmed cases is likely to represent only a small fraction of the true number of infections. And where the positive rate is rising in a country, this can suggest the virus is actually spreading faster than the growth seen in confirmed cases.