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  • You may have seen this chart since the start of the coronavirus pandemic.

  • In one image, it appears to capture the state of each nation's battle

  • in the global war against the virus.

  • But like all data visualizations, its design  tends to emphasize some things and hides others.

  • So here are 4 things we need to know to understand this chart.

  • First, this is not a chart of all coronavirus cases.

  • It's only showing us confirmed cases.

  • That means each line doesn't just reflect the state of the outbreak in a country, but

  • also how aggressively that country is testing people for the virus.

  • Take a look at Japan and South Korea earlier in the pandemic.

  • Japan's outbreak looked pretty small in comparison.

  • But the available data on testing shows us that South Korea had tested vastly more people

  • than Japan did, even though their population is less than half as big.

  • And now, as Japan slowly increases their testing, the outbreak there looks more worrying.

  • It's a good reminder that we can't understand case data

  • without some sense of the testing levels.

  • And that's especially true for lower-income countries

  • where we know their testing capacity is limited.

  • The second thing to know is that the scale for the y-axis on this chart

  • is a bit different from most charts.

  • It's called a logarithmic or log scale.

  • On a typical linear scale, you divide the space by adding the same value over and over.

  • The log scale is made by multiplying a value, in this case, ten.

  • 100 times 10 is 1000, times 10 is 10,000, times 10 is 100,000.

  • That means that there's no fixed amount of space on this chart

  • for a certain number of cases.

  • So the first 100,000 cases take up this much space

  • and then the next 100,000 cases get just this much.

  • The higher the numbers, the more visibly squished they become on a log scale.

  • So why do it this way?

  • Well, let's take the 5 countries with the largest outbreaks right now, and rewind them

  • back to March 17th.

  • On a linear scale, it looked like things were pretty bad in Italy

  • but the others were doing better.

  • The log scale offered a much clearer warning:

  • we were all on the same path of exponential growth.

  • It's the nature of infectious disease that numbers get big fast.

  • So it makes sense for numbers to get big fast on the chart too.

  • Fast forward a few weeks and the linear scale shows cases climbing and climbing

  • while the log chart shows curves that are flattening.

  • As governments have implemented lockdowns and social distancing, the virus is spreading

  • at a slower rate than before, which isn't very visible on the linear scale.

  • But keep in mind that the difference between this dot and this dot

  • is more than 32,000 people.

  • And the log chart tends to downplay just how many more confirmed cases there are in the

  • US than in the other countries.

  • Which brings us to the third thing to know

  • about our chart: it doesn't account for population size.

  • When you adjust for population, really small countries like Iceland and Luxembourg  appear

  • to have the biggest outbreaks for their size, which may reflect higher testing rates.

  • The US and China have much bigger populations so their curves drop a bit.

  • But the size of a country doesn't really affect the growth rate of its cases, and it

  • doesn't tell us much about how much the country is struggling.

  • It just pushes smaller countries up on the chart and tends to hide the fact that the

  • outbreak is especially bad in certain regions of bigger countries,

  • like the state of New York.

  • And the last thing to know about our chart is that the x-axis doesn't plot time by

  • the datebut by the number of days since the country

  • recorded 100 confirmed cases.

  • For Italy, that was February 24.

  • For Turkey, March 19.

  • When they're all layered on top of each other, it allows us to compare the trajectory

  • of the outbreaks, but it tends to obscure the fact that the

  • pandemic hit some countries before it hit others.

  • The world watched as tens of thousands of cases appeared in China.

  • Then big outbreaks in South Korea, Italy, and Iran, sent a message about what was to come.

  • Two weeks after South Korea reported its 100th case, the United States' did the same.

  • In a situation where actions taken early can have a much bigger impact than actions taken

  • later, time is a crucial factor. and we have to remember that some governments had more

  • time than others.

You may have seen this chart since the start of the coronavirus pandemic.


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B1 中級

コロナウイルスのチャートがいかに私たちを誤解させるか (How coronavirus charts can mislead us)

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    林宜悉 に公開 2021 年 01 月 14 日