What is a stacked bar chart and when to use one
What is a stacked bar chart
A Stacked Bar Chart is a Bar Chart where different groups are stacked on top of each other. Stacked Bar Charts are useful for comparing different categories of data while also seeing what contributed to each value.
The Stacked Bar Chart below shows property sales for three Real Estate agents broken down by what suburb they sold houses in.
We can see that John sold more property than Sally and Joe. We can also see that John sold a lot more property in Cashmere than Sally or Joe. If Sally and Joe see this graph, they might want to try sell more houses in Cashmere.
If we just had a regular Bar Graph then we would not be able to see that John sold most of his property in one suburb.
When to Use a Stacked Bar Chart
Stacked Bar Charts are useful when you need to compare different groups of data and also want to see a breakdown fo each group.
If the groups add together to make a whole, like what suburb was property sold in, then a Stacked Bar Chart is a good option. If the groups are different kinds of data, like Miles Per Gallon fuel efficiency and Engine Size, then a Grouped Bar Chart would be a better option.
What Are the Benefits of a Stacked Bar Chart
Stacked Bar Charts are useful for comparing categories of data and also looking at what makes up the total of each category. This is really useful if you want to look for reasons why one category might have performed better than another.
Going back to our Real Estate Sales example. The following Stacked Bar Chart shows that John has sold the most property and that he sold a lot of property in Cashmere.
If Sally and Joe see this graph they might wonder how John was able to sell so much property in Cashmere. Maybe he knows lots of people in Cashmere and it's easy for him to sell houses there. Or maybe it's just easier to sell houses in Cashmere, so Sally and Joe should spend more time there.
Compare this to if we just had a regular Bar Chart.
The Bar Chart still shows that John sold more property than Sally and Joe. But it does not tell us anything about how or where he sold it. If Sally and Joe see this graph they might not suspect that John is selling a lot of property in Cashmere.
What Are the Disadvantages of a Stacked Bar Chart
Stacked Bar Charts do let us know a bit more about our data than a regular Bar Chart. But they do have some downsides.
It can be difficult to compare sizes of different groups in a Stacked Bar Chart
It is very difficult to compare the sizes of different groups in a Stacked Bar Chart. Taking our Real Estate example, it is very difficult to compare how much property John, Sally and Joe sold in Lincoln.
The comparison is difficult because the stack for Lincoln is sitting on top of the stacks for Harewood and Cashmere.
It is a lot easier to compare how much property John, Sally and Joe sold in Harewood because Harewood is the bottom item.
If we need to compare how much property John, Sally and Joe sold in each suburb we can use a Grouped Bar Chart.
Now we can more easily compare how much property each salesperson sold in each suburb. But it is now really difficult to figure out the total amount of property sold by each agent.
The easiest way to see the total amount of property sold by each agent is to add another series to the groups for the total.
Adding a bar for total is not standard practice, but it does make it easier to see how much property each agent sold.
Stacked Bar Charts can be hard to read if there are too many stacked series
If there are a lot of series stacked on each bar then it can become difficult to figure out what series are important.
There are a couple of workaround that will enable you to still use a stacked bar graph effectively.
If you only care about a couple of the stacks on the bars, then you can filter your data so that you are only left with these stacks. This may also allow you to focus more on the groups you care about in other kinds of charts.
If you need to keep all of hte data, then you can reduce the number of stacks and move everything else into a stack called "other".
For example, if you were analyzing property sales data and only cared about two out of 50 suburbs in your city, then you could make stacks for "suburb A", "suburb B" and "other suburbs". This way you can still compare property sales in the suburbs you care about to the property sales in the "other" suburbs.
Stacked Bar Charts are a useful tool for comparing categories of data. They are especially useful when you need to see what contributed to the values of each category.
We looked at an example dataset of property sales. Visualising the dataset with a Bar Graph only showed us that one agent managed to sell a lot more property than the others. While using a Stacked Bar Chart showed us that this agent managed to sell a lot of property in one Suburb, and maybe the other agents should spend some more time in that Suburb.