Imagine you have a test where 0.1% of results show that you have the virus even if you don't have it. Now, if you test in a country like the US where 10% of tests show a positive, this won't make a difference to your results. If you now do this in New Zealand, where there are close to 0 people with COVID and lots of tests, for every 100000 tests you will still see 100 positive results. This article says that in such a situation where very few people have the virus, you should redo the test because it could be one of those 0.1% errors.
I’m sorry, could someone ELI5 this?
Imagine you have a test where 0.1% of results show that you have the virus even if you don't have it. Now, if you test in a country like the US where 10% of tests show a positive, this won't make a difference to your results. If you now do this in New Zealand, where there are close to 0 people with COVID and lots of tests, for every 100000 tests you will still see 100 positive results. This article says that in such a situation where very few people have the virus, you should redo the test because it could be one of those 0.1% errors.