I’ve heard something lately that initially gave me quite a laugh. And then I heard it again, and then again, realized people were believing it to be true, and then it wasn’t so funny.

The thing I heard was regarding Covid-19 infection numbers. It was this: “The reason we have so many cases of Covid-19 is because we test so much for it.” And, I guess that it followed in the speaker’s mind, that if we tested less we would have less Covid-19.

Now, tautologically, that sounds sort of true if we test everyone and our test is accurate, neither of which is the case.

If we were to count half the people in a room, we would come up with a number that is much smaller than if we counted everyone in that room. The number of people in the room would not change just because we only counted half of them, but that number would surely be smaller.

That is somewhat like Covid-19 testing. If you test a small number of people when Covid-19 is around, you would expect some but not all of them to be infected. If you test a larger number of people when Covid-19 is around you would expect a larger number of infections detected. And, it follows I suppose, that if you test no one, you would find no cases of Covid-19.

In all instances, however, from counting some but not all persons in a room to testing some but not all persons when Covid-19 is around, the counting and the testing do not effect the true number of people in the room nor the number of positive cases of Covid-19. The number of people in the room is whatever that number is, and the number of Covid-19 infections is whatever that number is, whether you counted or tested or not. The counting and the testing doesn’t effect the actual numbers of each period.

At least, for right now.

In our room population counting, if we only count some of those in the room, then wait a while, some may leave the room and some may enter, and thus the true number of persons in the room may vary. If we know how often people come and go usually, and about what proportion of the room’s population we counted, we might be able to guess at the actual population – but it would be only a guess. That type of guessing is what some people call statistics.

In the case of Covid-19 testing it is much the same. Based on our observations of a smaller group, we can guess how many people get Covid19, how many do not, how many people get well, how many do not. And using this basic statistical treatment, we can extrapolate to get an idea of the actual infection rate and the effects of Covid-19 in a larger population.

But, once again, in neither experiment does the counting effect the actual number. There are 114 people in that room right now and any way you count some or all or none of them, there are still 114 people there. There are 76 cases of Covid-19 infection in the population that you tested. And whether you counted 10% of them, or 1% of them, or 100% of them, there are still 76 cases.

Remember, when we counted some of the people in that room we had to know about how many come and go in order to estimate the number of people actually there. We also have to know the number of people who usually catch Covid-19 to get an accurate estimate of the cases when we test only a small portion of us.

So, in contradiction to the idea testing somehow increases the number of cases, it is easy to see how valuable testing can be to combat Covid-19. How? The same way we would control the number of people in our room-we would control entry. For Covid-19 positive cases we would quarantine, for everyone else we would wear protective gear (MASKS and GLASSES), operate hygienically (wash up a lot), avoid close physical interactions, locate and treat those who have contacted Covid-19 victims.

Not only does Covid-19 testing NOT increase the number of cases, but it can reduce the occurrence of Covid-19 by warning us where it presently is so we can take those precautions and limit further spread.

It is true that testing as I have used it here requires, REQUIRES rapid results notification because, as we all know, a test taken on Tuesday can only tell you that you had or did not have Covid-19 enough to show up on the test on TUESDAY. The longer after Tuesday you had to wait for the results of that test, the less helpful all those precautions, especially contact tracing, is going to be.

So, it seems so simple to understand how testing does not effect the number of persons who have Covid-19, but can drastically effect the number of persons who will catch it by taking immediate precautions when testing positive and general precautions before it gets you.

And because it seems to simple to understand, that’s why I laughed.