Hillary Clinton's presidential campaign just committed what can only be described as a data catastrophe.
The campaign, in promoting its gun policy agenda, sent out this tweet:
The general point is true: The great majority of Americans do support universal background checks, including the great majority of gun owners.
But this is simply not how Venn diagrams work. The circles are completely wrong. They should, for one, overlap entirely, since the gun owners referenced in this are all Americans. And the circle for Americans should be much, much bigger than the circle for gun owners, since gun owners make up just one segment of the US population. (That is, unless, the Clinton campaign is literally saying that a lot of gun owners are un-American, which is a very, very hot take for a risk-averse campaign.)
With that said, here's a rough approximation of what this diagram should look like if the campaign insists on using circles:
A reader made another version, which is slightly more complicated but makes the same point better (green is gun owners, purple is Americans who support universal background checks, and red is Americans who don't support universal background checks):
As you can see, these aren't even Venn diagrams anymore; they're Euler diagrams. That's because a Venn diagram was the wrong choice for this data point in the first place. Maybe what Clinton wanted was a pie chart, bar chart, or Euler diagram, or maybe she didn't even need a chart — an infographic with the numbers splashed in big letters could have worked.
Instead, we got an atrocity in data visualization.
In the grand scheme of things, this isn't the worst thing Clinton has done. (After all, she voted for the war in Iraq.) But this is pretty bad.