How to spot a misleading graph (Vol.1)
A toothpaste brand claims their product will destroy more plaque than any product ever made. A politician tells you their plan will create the most jobs. We’re so used to hearing these kinds of exaggerations in advertising and politics that we might not even bat an eye.
But what about when the claim is accompanied by a graph? After all, a graph isn’t an opinion. It represents cold, hard numbers, and who can argue with those? Yet, as it turns out, there are plenty of ways graphs can mislead and outright manipulate. Here are some things to look out for.
In this 1992 ad, Chevy claimed to make the most reliable trucks in America using this graph. Not only does it show that 98% of all Chevy trucks sold in the last ten years are still on the road, but it looks like they’re twice as dependable as Toyota trucks.
That is, until you take a closer look at the numbers on the left and see that the figure for Toyota is about 96.5%. The scale only goes between 95 and 100%. If it went from 0 to 100, it would look like this.
This is one of the most common ways graphs misrepresent data, by distorting the scale. Zooming in on a small portion of the y-axis exaggerates a barely detectable difference between the things being compared. And it’s especially misleading with bar graphs since we assume the difference in the size of the bars is proportional to the values.
So the next time you see a graph, don’t be swayed by the lines and curves. Look at the labels, the numbers, the scale, and the context, and ask what story the picture is trying to tell. Look out for more tips on reading graphs coming later this week!
From the TED-Ed Lesson How to spot a misleading graph - Lea Gaslowitz
Animation by Mark Phillips