How Many Have Been Tested for Coronavirus in the USA?

Number of People Tested for Coronavirus in the United States Chart

Number of Tests Per 1,000 for Coronavirus Chart

Total Covid-19 Test Per 1,000 People 

What can data on testing tell us about the pandemic?

Testing data provides us with two indicators of the quality of data on COVID-19

No country knows the true number of people infected with COVID-19. All we know is the infection status of those who have been tested.

The total number of people that have tested positive – the number of confirmed cases – is not the total number of people who have been infected. The true number of people infected with COVID-19 is much higher.

Whilst there is no way to infer the true number of infections from testing data, it can help give us a strong indication of the quality of a country’s data on the pandemic and an idea of how informative the number of confirmed cases in a country may be.

Testing coverage

The chart here shows a measure of testing coverage – tests per thousand people.

Countries are reporting testing data in different ways: some report the number of tests, others report the number of people tested. This distinction is important – people may be tested many times, and the number of tests a person has is likely to vary across countries.

Across different countries, we see an enormous range in testing coverage. In Iceland there have been more than 100 tests per thousand people – far more than in any other country. In Indonesia, testing coverage is very low – only 0.1 tests per thousand people.

Generally, we would expect that more testing means more reliable data on confirmed cases, for two reasons.

Firstly, a greater degree of testing provides us with a larger ‘sample’ of people for which their infection status is known. If everybody was tested, we would know the true number of people who are infected.

Secondly, it may be the case that countries with a high capacity for testing do not need to ration tests as much. Where the capacity for testing is low, tests may be reserved (or ‘rationed’) for particularly high-risk groups. Such rationing is one of the reasons that tested people are not representative of the wider population.

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