Why is zero important in a bar graph?

data viz tip May 03, 2022
A bar graph showing the number of penguins with an overlay to show bar size comparisons.


Why is it important to always start the axis of a bar graph at 0?

Meet the Palmer Penguins. This is a dataset of penguin observations at the Palmer Station in Antarctica, collected and made available by Dr. Kristen Gorman. We will use the Palmer Penguins dataset to explore why it's important to include 0 on the axis of a bar graph.

Let's see how many penguins of each species are in the dataset. Counting the number of penguins of each species, we get this first bar graph. Notice the x-axis starts at 0.

Because the axis starts at 0, we can make an accurate comparison between the length of the bars.The Adélie bar is more than twice as long as the Chinstrap bar.

What if we decided to zoom in so we could see the difference in the number of penguins by species more clearly? Notice the x-axis now starts at 40.

Now, because the axis does not start at 0, the comparison between the length of the bars is distorted. The Adélie bar is now four times as long as the Chinstrap bar.

So, it's important to always include 0 in a bar graph! Otherwise, your audience will draw incorrect conclusions about the data.

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