“Always” start your bar charts at zero
It’s great to represent data visually with an aim of uncovering insights and communicating effectively from data.
We know there are all kinds of data visualizations out there, from a simple line chart to complicated diagrams that represent many dimensions of data in the smallest real estate.
One thing every analyst needs to be mindful of is — are they giving an accurate message via their charts?
Let’s look at one of the most common charts i.e. bar chart also known as a column chart, representing sales for Q4 of 2021 and 2022.
It is clear from size of these bars that second one is almost twice in length to the first. Does that mean that sales have doubled this quarter? Not really.
Now, look at the below chart which is an accurate visual representation of the growth in sales i.e. less than 20%.
The only difference between the two charts is the base value they start at. The first one starts at 24 million dollars while the second at 0.
In a bar chart, the length of the bar represents the data value i.e. longer the bar higher the value. The higher the base value, lesser the portion of the actual length that will be visible above the base line.
Here, only 6 million dollars i.e. 30–24 is represented for 2021 and 11 million dollars i.e. 35–24 for 2022. That’s almost double, an optical illusion.
This is not the case with line charts as over there the data points are viewed relative to each other and not necessarily from the base.
I never thought I’ll write a story on this. But this had to be told.
Have you seen or created bar charts that don’t start at zero?
