How to Read the COVID-19 Graph
When you see a flat line on a chart, it’s tempting to think, “Oh, at least the situation is not getting worse!” But one of the common types of charts we see for COVID-19 is the number of new cases per day. In this case, a flat line means that things are actually getting worse.
For example, here is the Financial Times graph of new COVID-19 cases, highlighting the United States.
To be clear, this is not a bad or misleading diagram. He says what he says. But we arrive at these charts with some assumptions and often don’t read the title and axes very closely. So let’s take a look at what we are actually looking at.
So, it looks like our curve is flattening from day 35 onwards, even slowly declining. But since this is a graph of new cases per day, our epidemic is actually still getting worse. It says that in the last month we have added over 20,000 cases per day.
If there is a flat line on such a chart, it means that the actual number of observations increases linearly. If my child poured twenty buckets of dirt onto the porch and I told her to stop, I would not consider the situation resolved if she continued to “only” pour twenty buckets onto the porch tomorrow and twenty more every day. thereafter. The muddy porch situation will get worse and worse.
Let’s try this instead. The Texas Medical Center has a nice graph that shows both new cases per day and the cumulative total of cases in the Greater Houston area:
This is not exactly the same as “how many people are sick with COVID right now,” because after a few weeks people either recover or die. (As far as I know, there is no easy way to get accurate data on how many people are currently sick.)
So what are we looking for in such a graph? When the pandemic is over, we expect to see the following:
- The number of new cases per day (blue bars) should be reduced to zero
- Cumulative cases (red line) should flatten out
On the contrary, when the situation gets worse, we expect to see:
- New cases per day (blue bars) are on the rise
- Cumulative cases (red line) are getting steeper
Other factors are important in these charts, including a linear or logarithmic scale on the vertical axis, whether the numbers are for the population or for the general population. You can also ask where the data comes from and know that there is a delay (often several weeks) between a person’s illness and their data being plotted on a chart. The lag in deaths is even greater than in accidents.
So there is something to think about, but for now it is good to know at least one thing: for everything to get better, we need to see how new cases get closer and closer to zero, and not just level out.