Column: An inability to understand numbers may be why COVID continues to spread
Here’s a three-question quiz. The questions involve numbers, but no calculation is required.
Question 1: A virus is circulating. The number of infections in a month rises 25 percent from January to February, then drops 25 percent from February to March. Is the number of infections in March (a) larger than the number in January, (b) smaller than in January, or (c) the same as in January?
Question 2: Two viruses are circulating, Epsilon and Upsilon. Epsilon’s case fatality rate is twice as high as Upsilon’s, but Upsilon is twice as transmissible. Other things being equal, which virus will kill more people: (a) Epsilon, (b) Upsilon, or (c) no difference?
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Question 3. Jamie and Lauren are both vaccinated against a virus. The vaccine is 90 percent effective. Jamie lives in a community where 80 percent of residents are vaccinated, while in Lauren’s similarly sized community only 40 percent are vaccinated. Who is more likely to become infected: (a) Jamie, (b) Lauren, or (c) no difference?
The quiz is a test of numeracy, or numerical literacy. Numeracy involves not just skill in calculation, but also basic numerical common sense: an intuitive understanding of relationships among numbers and how they are affected by operations.
The above quiz is simple, but many people probably got some questions wrong. Innumeracy is a serious problem in society. It is the numerical cousin of illiteracy, less well recognized but more common, even among educated people. Millions of Americans are functionally innumerate, unable to interpret percentages, graphs, statistics, probabilities, and other kinds of basic data that they encounter.
In a pandemic, fatality rates, transmissibility, mitigation measures, and vaccine efficacy are numbers games, all widely misunderstood. Three studies conducted early in the pandemic and published in the Proceedings of the National Academy of Sciences examined the relationship between numeracy and support for social distancing measures. The correlation, it turns out, is clear: less numerate people are more likely to oppose strict public health measures.
Unsurprisingly, given the bizarre intersection of politics and public health, innumeracy also appears to have a political dimension. The researchers tracked political leanings and found that while numeracy is poor across the political spectrum, it is even worse among self-identified conservatives. Could this have something to do with the fact that death rates are now much higher in red counties than in blue ones?
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In any case, a numerate person should recognize quickly that the correct answer to all three of the above questions is (b). Question 1 should be easy: the decrease more than offsets the increase because it is 25 percent of a larger number.
In #2, the effect of an increase in the fatality rate is linear, while the effect of an increase in transmissibility grows exponentially over time. In the long run, Upsilon will infect more than twice as many people as Epsilon and therefore will result in more deaths, notwithstanding Epsilon’s higher fatality rate. This is what has made COVID-19 so insidious all along: its low fatality rate bamboozles people into thinking that drastic, life-altering measures of control are unwarranted, even as hospitalizations and deaths skyrocket as a consequence of the uncontrolled transmission.
In #3, the virus will spread more freely in the less-vaccinated community, so Lauren is more likely to be exposed than Jamie. As long as the vaccine is less than 100 percent effective, Lauren is therefore more likely to be infected. This is why unvaccinated people are, in a statistical sense, a menace to society.
More broadly, one could say the same thing about innumeracy: it can kill us.
Julian Hook is a resident of Bloomington.
This article originally appeared on The Herald-Times: Column: Numeric literacy affects whether you understand COVID stats
