Showing two main points on one chart

It’s (usually) fairly straightforward to choose a chart type when you know what the main point you are trying to get across is. Is your message that there has been a change over time? Do you want to show a difference between groups? There are all kinds of online chart choosers to help you do this (here is one of my favourites). But what about when you have two main points to make?

I was recently working on a chart where I wanted to make the following two points:

  1. 2016 was the only year that participants had a statistically signifcant increase in health ratings; and
  2. participants had lower health ratings pre-program in 2016 vs. other years

I started with the chart below. Here the different color used in 2016 really highlights that something different happend that year (half of point #2), but it is difficult to see the change over time (point #1, half of point #2):


Alright then, let’s change to a line graph. It is much easier to see the change over time. However, the statistical change in pre- and post-test scores was important to the program and they wanted to highlight that. That piece of information isn’t easy to see here.


I added a transparent rectangle to highlight the difference between pre- and post-test scores and this is the result:


I think that this chart nicely conveys the two main points that I wanted to make and is a vast improvement over the first chart. It also goes to show that it’s worthwhile to play around with different chart types while working on reporting!

Note: I have changed the results to fictional data to keep things anonymous

data viz tools

Awhile ago I posted about the data viz catalogue. It’s a neat resource that helps you choose a visualization that best tells the story of your data. The creator has recently posted a roundup of the 20 best tools for data visualization. It includes tools that have no coding required as well as tools for developers. There were definitely a couple that were new to me and I look forward to checking them out.

On my 2016 to-do list: learn enough coding that I can play around with the dev tools.

Data Viz Catalogue

I just came across this great data visualization resource through BetterEvaluation – the Data Visualization Catalogue. Choosing a chart or other visualization type that best tells the story of your findings is the most fundamental part of data visualization. This site helps you by allowing you to search data visualizations by function.



Once you choose a function, it will give you some suggested visualization types:



Very neat!

The site was created by Severino Ribecca and will be added to over time.