Showing Variance When Your Data Doesn't Have Much
Ever create a bar or line chart and get frustrated that the chart doesn’t show a lot of change from mark to mark? Here are some design tips to help highlight the changes in your data.
The example we’ll use is a bar chart showing percentages by regions. All the values are within 3% points of each other, making it hard to see which values are higher or lower. Choosing the right chart type should be based on your data, but sometimes you can’t change it. These tips will discuss how to make small changes to highlight the variance. Let’s get started!
This is some fake data I made in Excel and brought into Tableau (tip in a tip: you can just copy paste data from Excel to Tableau and it will treat it like a datasource!)
Tip #1 Add a reference line
As part of our Data Coach course, we cover what we call ideal and less than ideal chart types (think: pie charts). The thing that ultimately makes a “bad” charts hard to understand is they lack a common starting point. However, we can highlight the variance in our data by adding a common end point, using a reference line.
To create a reference line:
1) Right click the axis and select “Add a reference line”.
2) Select Line (if it isn’t by default). Select the Constant option and put 1 in the Value box. Select a line color and weight that provides a good amount of contrast from the chart and marks design. Click ok.
Now you’ve got a solid line close to the end of the marks where users can easily compare the difference.
Tip # 2 Change the chart type
It’s not an option to remove 0 from the bar chart and using a line chart isn’t an option for categorical data. However, we can change the mark type to a dot plot and then get rid of the 0.
1) Change the mark type to Circle
2) Right click on the axis and uncheck Include zero.
You can keep the regions split out or combine them and use color and / or labels to distinguish between them.
Tip 3 - Dual axis charts and calculated fields
This option is a little more challenging, but is doable if you follow along step by step.
From our original bar chart, we’re going to add more marks to highlight the variance from 100%.
The final product will look like this:
1) Create a calculated field which get the sum of your % measure and subtracts it from 1. ex: 1-SUM([Percent Measure])
2) Hold down the Control key and add a copy of your measure to the Rows shelf.
3) Change the Mark Type in the 1st accordion on the marks card to Gantt Bar. Add Delta from 100% (or whatever you named the calculated field in step 2) to Size.
4) Right click on the copy of your measure on the Rows Shelf and click Dual Axis.
Voila! There’s some other formatting things that need to be done, but that’s the bulk of the work.
In this post, we quickly covered three ways to highlight the variance in your data when it doesn’t have much. If you like this content, be sure to stay tuned as we make more of it directly available to you through Data Coach.
For more details on the methods use in this post, download the workbook from Tableau Public.