Testing vs. Cases
One of the issues with the number of new cases is that, as Nate Silver has at this point famously said, the more testing you do, the more cases you’ll have. However, I would argue it is not that simple. The question is: WHY are we doing more testing?
The relation between cases and testing can go both ways. Yes, more tests mean more cases, but we are probably doing more testing because we suspect people are infected. Let’s take this to the logical extreme: If there was no coronavirus, we’d do ZERO testing. In other words, we are doing testing because we suspect that people have the virus.
Some people have suggested percent positive is the thing to look at. But that may become less reliable as some people get tested over and over again (think sports players). They are not getting tested because they got exposed – it’s just precautionary.
Instead, I’m going to focus on hospitalizations. Assuming the criteria for hospitalization has stayed constant, you can use that as an indication how many cases there are.
I am also going to remove NY and NJ from this comparison as they haven’t really reopened yet (today is their reopen). Here’s the graph.
In my mind, I see four phases. The first is of course when cases were building. The second is when we saw both hospitalizations going down and new cases declining. We probably had about the same relative level of testing.
After that, we increased testing a lot. We found more cases, but probably the prevalence of the virus was decreasing as hospitalizations were decreasing at the same time. I’ll call Phase III the Nate Silver phase.
However, now, we see that cases are spiking and hospitalizations have started to go up as well. Thus, it seems now that the jump in cases is not due to more testing but more cases.
Cases are important. Look at Newport Beach – several restaurants had have to close again because employees have tested positive. New cases eventually will hurt the recovery.
The next question will be do deaths follow? That’s another post for another time.