'Persons tested' vs 'Samples tested'

When comparing testing activity, it is important to realize that some countries are reporting on the amount of 'persons tested' and some countries are reporting on 'samples tested' (or simply 'labtests done'). Many news analysts, COVID-trackers and even governments have been incorrectly mixing the data, while in fact these numbers cannot be compared as the number of samples tested is always higher than the number of persons tested.

As an indication, in countries reporting both numbers, the amount of 'samples tested'/'labtests done' is calculated by multiplying the amount of tested people by: 1.55 (Italy), 1.42 (UK), 1.48 (Japan). Below I will compare countries who report on 'persons tested' seperately from countries who report on 'samples tested'.

Comparing testing activity per capita (last 7 days)

To give a good indication of how many tests are being done in a country, here I compare the testing activity using a 7 day average to correct for jumps or drops during weekends. Also, I take into account the population-size in a country, by dividing the daily number of tests by the number of inhabitants (in millions) a country has.

As can be seen in above chart, it's not necessarily true that big countries can't process a high number of tests per capita compared to smaller countries: both Russia and Italy are countries with a large population and still are on the top of the list. The above chart also shows that Nigeria, Bangladesh and Argentina have been doing very few COVID-19 tests recently, compared to other countries.

Looking to the same comparison for countries reporting on 'persons tested', it's easy to see that Denmark and Luxembourg have been testing most people recently. Even more, if Denmark and Luxembourg would have been reporting on 'samples tested' the number would have probably be 30%-60% higher, which means Denmark and Luxembourg are currently the countries with the highest testing activity of the 38 countries with daily testing statistics in the Newsnodes database.

Comparing positivity rate (last 7 days)

As explained previously in this article, positivity rate can help to get a rough indication about to what extent countries are underreporting COVID-19 cases. Example: if a country would announce that 50% of those tested turn out to be SARS-CoV2 positive, this is a strong indication that there are many undetected cases still spreading the virus. The positivity rate is here calculated by dividing the number of new confirmed cases by 'samples tested' (or 'persons tested').

Looking to the above chart, a few things are notable:

• Nigeria is not only one of the countries currently doing the fewest tests per capita in the world, it's also the country with one of the highest positivity rates in the world.
• Chile, which is (in contrast to Nigeria) currently doing quite a lot of COVID-19 tests (see first chart in this article), still takes the second spot for highest positivity rate!
• Also Bangladesh is likely to be underreporting cases and deaths at this moment, as illustrated by the fact they are doing very few tests per capita currently, while at the same time having a high positivity rate.

Looking to the same comparison for countries reporting on 'persons tested', I'd like to highlight a few things:

• South Korea has topped Denmark in having the lowest positivity rate recently. That's interesting, as South Korea is actually not testing that many people recently. While most countries have been rapidly increasing their testing activity in recent months, South Korea is currently still below the level of testing activity they had in early March when South Korea tested ~15000 persons per day.
• There are big differences between African countries regarding the positivity rate. While a country like Guinea currently has a positivity rate of over 20%, the positivity rate in South Africa and Morocco are below 5% and hence lower than the United Kingdom.
• Finally Peru has to be mentioned: Peru is currently the only country in the world which is reporting is in top 10 worldwide with most cases per capita, most deaths per capita.(source) On top of that, while they are testing quite a lot, still Peru is also reporting a very high positivity rate of 17%.

Final note:

Contrary to data on cases and deaths, where we have daily data for every single country in the world, we do not have testing data for all countries worldwide. Do you want to see your country included as well? You can help us by creating an account on Newsnodes.com and submitting data for the country you want to be included!