The previous post mentioned some of the problems with COVID testing, extracted from a massive article by Nate Silver.
More than a year ago Silver, author of “The Signal and the Noise: Why So Many Predictions Fail — But Some Don’t,” set out to explain to a baffled public the vagaries of the testing situation. Although people hold many different assumptions, the basic realities of statistical computation have not changed.
The author illustrates in meticulous detail several major ways in which testing methodology can skew results, and pursues the questions of why and how the reported case counts “can differ from the actual number of infections.” Those are ominous words.
The first thing to realize is that countries do things differently, and even within a single country, there is a vast disparity between the practices of different states, counties, provinces, districts, and cities. Melding this universe of mandates, compliance, resistance, and data together into a meaningful picture is no easy task, and just about everything needs to be taken with a grain of salt.
We think of mathematics as abstract and pristine art, but producing the numbers that statisticians have to work with can generate numerous “messy, real-world problems.” For instance, unless a government makes incredibly strict rules, and enforces them relentlessly, no one can know the number or percentage of asymptomatic cases.
Epidemiology 101
Silver writes,
The most important number in any epidemiological model is R, or the reproduction ratio, which is how many people that a person in one generation passes the disease along to in the next generation. For example, if a disease has an R of 3, that means each infected person transmits it to three more people […] which becomes nine people, which becomes 27 people, which becomes 81 people, and so forth — the very nature of exponential growth is that it gets out of hand quickly!
This is a point that Childhood Obesity News has made many times, chiefly with the classic parable of the chessboard. There is also a solid mythological reference. Somehow sensing that creatures capable of infinite multiplication existed, the ancients spoke of a monster called the Hydra. “It had many heads and every time someone would cut off one of them, two more heads would grow out of the stump.”
Similarly, the coronavirus’s insane, monomaniacal drive to reproduce creates a crushing onslaught. Time is a very important factor, too. One problem is that…
[…] there’s a long lag between when someone is infected, when they develop symptoms, when they get tested and when those test results are reported. In Wuhan, China, the lag between the development of symptoms and test results being reported was around 10 to 12 days. And considering it usually takes at least a few days for symptoms to develop, the lag between infection and a case showing up in the test statistics is going to be longer still.
Your responses and feedback are welcome!
Source: “Coronavirus Case Counts Are Meaningless,” FiveThirtyEight.com, 04/04/20
Image by Biodiversity Heritage Library/Public Domain
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