During the coronavirus outbreak, should we change the data visualization rules?

Alice Casey raises an interesting point about a chart about coronavirus (“What are the chances of dying? from the BBC):

What’s the problem? It’s that the bar extends all the way to the right. We perceive this as a “maximum” value. Our eyes stretch to the right, and the risk is we perceive that to mean 100%. The implication being that 100% of 80yr olds who get the disease will die. That is enough to worry anyone.

We perceive a bar that is full length to be max value. In this case, that might be 100%

Of course, the information is on the chart – down in the bottom right. The 15% label is clear:

The max length is only 15%

Is this a mistake? In most cirumstances, it’s not. When we’re communicating data, we’re normally trying to make it easy to compare one mark against another. By truncating the axis to 15%, the reader can easily compare one category against another.

However, at this time, our responsibility is to communicate all the data. Here are 2 ideas. On the left, I’ve labelled the bars: people will see the values as they see the bars. On the right is, I suspect, the chart that Alice wanted to see. I also changed the title to be a question.

Two makeovers

I think both of these are improvements, but what we need is to add the missing data: those who survived. Furthermore, where does this death rate come from? Is it consistent around the world? The numbers refer to 44,000 coronavirus cases in China, as published in a report by the Chinese Centre for Disease Control and Prevention. The death rate in China isn’t necessarily the same around the world. Digging into table 1, the death rate seems to be going down, too. So a chart like this might not apply in your country.

With this in mind, my final version is below. It shows survivors and has a more descriptive title:

A makeover showing survivors as well as those who died.

I much prefer this version. The blue bars are concerning, especially for the elderly or those with some health conditions. But the grey bars are, in all cases, far bigger. This visual clue shows a reality of coronavirus: it’s a very serious disease, worthy of a major global response, but not as dangerous as the original might have led us to believe.

EDIT: Chris Love tweeted that perhaps you could visualize the survival rate more prominently than the death rate:

That’s a great idea – this way, the data remains accurate, but greatly reduces the chance people could be alarmed. Jorge Camoes and Alberto Cairo also tweeted good arguments for the original chart.

What do you think? Is my makeover less alarmist?

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