Slopegraphs for Visualizing Two Points of Change
Slopegraphs are an excellent chart choice for visualizing the change or difference between two points in time by category.
Except, relatively few data designers, presenters, and practitioners are aware of them.
Slopegraphs are one of the best kept secrets of the data visualization world. They almost feel too simple, and yet, simplicity is the key to communicating data quickly, clearly, and accurately. It’s my experience that simplicity is what transforms numbers into insights.
[box type=”info”] This post is part of a new series on non-standard data visualization charts called “Fantastic Graphs and How to Make Them”.[/box]
A slopegraph is a line chart that plots measures of categories on two vertical axes. The lines connecting the axes create a slope that allows the viewer to clearly see the difference or change.
Think of it as a “zoomed in” view of a regular line chart with only two points. Measuring change between two points in time is the most common usage, but the structure may be used to measure the difference between other variables like segments or survey answers.
Now, here’s the rub. As of yet, I haven’t found any commonly available data visualization tool to have slopegraphs available out-of-the-box (except for a PowerPoint plugin tool called Vizzlo). At time of writing, you’ll need to create with some legwork and creativity in Excel or Tableau most easily.
But that’s not necessarily a bad thing. Sometimes, it’s fun to roll up our sleeves and tinker with default charts to create something more useful and visually appealing!
When Should I Use a Slopegraph to Visualize Change?
There are several chart choices available to represent differences or change over time by category. The most well known option may be the clustered (or grouped) bar graph. However, the clustered bar is an example of a chart that’s commonly used and available but has major comprehension limitations.
A clustered bar chart similarly lets you compare two data points for multiple categories. However, its structure is only suited to help you compare two points of data within one category. It isn’t visually effective at allowing you to compare the categories to each other.
Take a look at this example:
Think about how quickly you are able to answer these questions:
- Which page increased in abandonment rate?
- How do the changes in abandonment compare to each other? Are they similar?
It’s likely that you’re able to individually evaluate the differences between each category, but it’s slowing you down to compare the categories because the intermittent bars create interference. And as soon as you go to three or four points per category, it's nearly impossible draw meaningful comparison between categories.
Every second counts when it comes to presenting information clearly. The goal of data presentation is to create instant crystal clarity for your audience.
Slopegraphs solve for this issue. The reason why you would choose a slope graph is that you want to not only quickly compare the difference between two points for each category, but you also want to compare each category to each other.
Here are some digital marketing scenarios where you can use slopegraphs to visualize change:
- Comparing the abandonment rate of website pages before and after a redesign
- Comparing year-over-year or month-over-month change in online channel conversion
- Comparing Yes or No answers by survey respondent segment
Now that you know why and when you should create a slopegraph, let’s show you how to create one that is clean, clear, and super brain-friendly!
How to Create a Slopegraph in PowerPoint (Or Excel)
Before we dive in, it's important to note that if I'm presenting data live, my gold standard is inserting charts and plugging the data right into PowerPoint natively.
I go into depth behind my reasoning in this blog post; in a nutshell, native PowerPoint charts can be resized to any dimension and maintain their sharpness. It also avoids the dreaded “broken link” error when copying charts from Excel that aren't sent along with the PowerPoint file.
CREATE
☐ Start by setting up your data table in Excel. You’ll want your categories (each line) on separate Excel rows on the left, and your before/after (or two points) values as columns. I’ve created a sample data set in Google Sheets you can use to follow along. {Make a copy to customize the data.}
☐ Click and drag to highlight the entire table. Copy the table. ☐ In either Excel or PowerPoint (my choice) go to Insert → Charts → Line → 2-D Line with Markers (this is the ONLY time I use line charts with markers!)
☐ In the Excel file that opens up, paste the data from the Google Sheet or another data file.
☐ Grab the lower right handlebar and move to the outside of the “After” column” (you don’t need Series 3.)
☐ Return to PowerPoint; your chart should look like this:
☐ Click to select the Chart. In the Chart Design tab, click Switch Row/Column so that you have two points along the X-axis. You can already start to see the slopegraph take shape here:
☐ The end goal, though, is to have the lines stretch to the edges of the chart. Note: if the Switch Row/Column button is greyed out, click Edit Data in Excel again to reactivate it.
☐ Right-click on the X-axis and click Format Axis.
☐ In the right dialog, look for Axis Options → Axis Position → “On Tick Marks”. Now the lines should stretch to either side of the graph.
☐ Now that we have the chart structure in place, we have a bit of formatting and detox to do.
DETOX + DECLUTTER
☐ Delete the horizontal gridlines, y-axis line, and the legend, since we’re going to label the line endpoints directly. Look how much cleaner that looks already!
☐ Next, we’ll make the lines thicker and the endpoints larger. We’re also going to use different shades of gray to form the baseline of our story. I know it sounds boring, but you’ll see the reason soon.
☐ Click the first line to select for formatting.
☐ In the Format Data Series right dialog, click the Paintbrush tab. Go to Line → Width = 4pt. ☐ Change the Line Color to medium-light shade of gray (I like hex #999999).
☐ Click the Marker sub-tab. ☐ Under Marker Options, click Built-In → Size = 10
☐ Under Fill, click Solid Fill → Color = same gray (#999999). ☐ Under Border, click No Line.
☐ Right-click on the same line and click Add Data Labels. This will add the percentage values to both markers on each line. If the lines are overlapping the labels, click on the Plot Area and adjust inward to make room. Move the data labels if necessary.
☐ Click on the data labels to select and change the font color to match the line color. ☐ Go to the mini Chart tab and de-select Show Leader Lines.
☐ In the Separator drop-down menu, choose “Space”.
☐ With those labels highlighted, carefully click on just the left label so that it is the only one highlighted. Then right-click on that label and select Format Data Label.
☐ Under Label Options, check Series Name so that the category label will be added, but only on the left point.
☐ Change the Label Position to Left.
☐ Repeat these formatting steps for the remaining lines, markers, and labels.
☐ Click on the entire chart to change to a readable, sans serif font of your choosing (I prefer Franklin Gothic Condensed). Make the font size at least 20 pt for live presentations, 15 pt for printouts.
HIGHLIGHT YOUR STORY
☐ Choose a standout color such as blue for positive emphasis or deep red for negative emphasis on a specific line. This is where you get to tell your unique story.
☐ Place your insight at the top as the chart title, and match the color of the category to the data point in your chart. And be sure to source your data at the bottom in small text.
And voila! You have a beautifully, clean, clear, and comprehensible slopegraph for displaying the difference or change in categories between two points. To speed this up, you could create a macro specifically for repeating those same formatting actions. But for me, it's worth taking just a few minutes to format it right and create templates I can reuse.
If you’d like to play with slopegraphs, click below to download my free slopegraph tutorial checklist and a ready-made template you can plug your data directly into.
I do recommend learning the mechanics of building this simple, yet powerful graph for visualizing change between two points for two or more categories.
However, if you’re truly pressed for time, check out the new visualization tool I’ve discovered called Vizzlo. It’s a PowerPoint plugin for creating non-standard chart types like slopegraphs really quickly!
TELLING YOUR DATA STORY WITH A SLOPEGRAPH
Here are two common ways you might share your slopegraph story:
- Through a live presentation
- Through a printed or email report visual
Let's go through these two paths to persuasion:
THOUGH A LIVE PRESENTATION
If I were presenting this data story in a live setting like a performance readout, I’d want to use intentional animation and cinematic build techniques. When presenting data stories live, I use a form of Freytag’s analysis of the classical three-act play, or narrative arc. It follows this format:
- EXPOSITION: What happened?
- RISING ACTION: Why do we think it happened? What surprised us about it?
- CLIMAX: What do we recommend? What is the cost of not taking any action?
- FALLING ACTION: Audience objections to recommendations
- DENOUEMENT / RESOLUTION: The finalized plan of action
For my slides, I use a step-by-step “build” technique to support each of my plot points as I'm speaking. My data storytelling “script” may go something like this:
EXPOSITION
“As you know, we completely rebranded and refreshed our website last quarter with many usability and design enhancements. We decided to analyze how the update impacted the abandonment rate of key navigation pages. Here are the pages we looked at:”
{show blank slide with just the list of pages EXCEPT for Contact Us}:
“As you’ll see in this visual, this order represents the pre-update abandonment rate of our primary pages, with the Homepage understandably first, and Contact Us thankfully last.”
{Animate in the pre-update data points, data labels and left axis and data labels}:
“Now here on the right, we have the abandonment rates after the site updated. We were pleased to see that abandonment decreased across all of our main navigation pages by at least 10 basis points…
{Reveal full lines and right side of the graph}:
“We were especially happy to see how much abandonment on the homepage dropped, by from 82% to 62%! We credit the improved layout above the fold based on our survey enhancements.”
{Highlight the Homepage line and labels in blue to emphasize}:
RISING ACTION
“It was great to see every primary page improve…except for one page. One of our pages actually increased in abandonment after the update. Can anyone guess what that is?” (Pause and wait, creates anticipation and participation)
“It’s the Contact Us page! We saw a 27% increase in abandonment after the update. Upon closer look, we noticed that the site update drastically impacted the layout and visibility of the contact form, possibly driving down completion.”
CLIMAX
“We recommend immediately working with the UX team to identify how to move the form back above the fold while preserving the new update features. We’ve calculated that this increase in abandonment can translate to losing an estimated 500 sales inquiries per month. If we don’t take action now, we could $50,000 in potential sales if we let this go for another 2-3 months.”
FALLING ACTION, DENOUEMENT
In these two parts, you would address any concerns or blocks your audience has with your recommendations to solve the issue, and leave the presentation with a clear action plan. Commence riding off into the insight sunset!
The way I just told that story leveraged cinematic techniques including suspense and climax, while visual tools included slow reveals and color emphasis.
SENDING AS A PRINTOUT
If you’re sending this over email or as a printout, you’ll want to leave enough space for all annotation and story on the view.
Here’s how I would use the white space on the right to annotate the slopegraph with my data story:
This is just a sample of the tools you can use to make your story memorable and actionable, and are just a sample of what you’ll learn in my Data Presentation + Storytelling Bootcamp online course.
FINAL THOUGHTS ON SLOPEGRAPHS FOR VISUALIZING CHANGE
While there are many complex graphs available in data viz platforms that might deliver the “wow” factor, sometimes the most effective and intuitive graphs aren’t found out of the box in any tool…yet.
Luckily, there are charts in the world like slopegraphs that may require a bit of elbow grease, but they are well worth the investment when they deliver your insights clearly, accurately, and intuitively.
Because unclear and confusing graphs are one slippery slope. (couldn't resist!)
Namaste, Lea
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