Sep 152015
 

Overview

Figure 1 – Bar charts are better than pie charts are better than donut charts.  Most of the time.

Figure 1 – Bar charts are better than pie charts are better than donut charts.  Most of the time.

As anyone who has read this blog knows I’m definitely a “bar charts are better than pie charts are better than donut charts” kind of guy, at least when you need to make an accurate comparison.

But in my classes, as I rearticulate the case against pies and donuts, I find myself wondering if there are in fact times when a pie chart might be a better choice.

Most of my data visualization work is for internal purposes so I focus on making it easy for people to make an accurate comparison.

But as my clients and I make occasional forays into public-facing visualizations I think about how to make it easy for people to make an emotional comparison.  By this I mean that I want people viewing the visualization to just “get it”.

Better yet, I want people to get it, be engaged by it, and in some cases, “feel” it.

With this in mind, in this post we’ll explore cases where

  • a pie chart is in fact as good, if not better, than a bar chart.
  • circles and spheres do a better job conveying magnitude than do bars.
  • a waffle chart produces an emotional wallop without compromising analytic integrity.

Where a pie chart trumps a bar chart

So, it’s the year 2034 and in this somewhat dystopian future there’s a movement afoot to add an amendment to the US constitution banning the use of pie charts.

Those of you familiar with the United States Constitution know that three-quarters of the states need to approve an amendment for said amendment to become law.  In 2034 it turns out the 39 of 50 states will in fact ratify the amendment.

Does that get us the needed 75%?  Here’s a simple, compact chart that lets us know immediately.

Figure 2 -- The amendment banning pie charts passes as I can see that the "Yes" votes fill more than three quarters of the circle.

Figure 2 — The amendment banning pie charts passes as I can see that the “Yes” votes fill more than three quarters of the circle.

It’s so easy to see that the “Yes” votes fill more than three-quarters of the pie that I don’t need labels indicating the large slice is 78% and small slice is 22%.

Compare this with a bar chart.

Figure 3 -- Did the "Yes" exceed 75%?  Without labels it's very hard to tell.

Figure 3 — Did the “Yes” exceed 75%?  Without labels it’s very hard to tell.

Without labels showing the percentages I cannot tell for sure if the “Yes” bar is more than three times larger than the “No” bar.

Okay, Okay, Okay!  I know that a simplified bullet chart would work, too.

Figure 4 -- A bullet chart shows that we've exceeded the goal.

Figure 4 — A bullet chart shows that we’ve exceeded the goal.

Yes, the bullet chart makes it clear that I’ve exceeded my goal but I need to know that the goal was 75%.  I don’t need the goal line with the pie chart.

So, does this mean that it’s okay to use pie charts instead of bar charts?

No.  Based on this example it’s only okay to use a pie chart (singular).  In addition, your pie chart (singular) needs to meet the following conditions:

  • One of the slices has to make up at least 50% of the pie.
  • If you’re pie has more than two slices you don’t ask people to compare the smaller slices.

Where circles and sphere’s do better than bars

As we all know Jupiter is big, really big.

Just how much bigger is it than Earth?

Should I create a bar chart to show this? If I were to create one should I compare the radius or the surface area of each planet?

Or should I really go nuts and compare the volume of the planets?

I don’t think the dashboard shown above is nearly as effective as the visualization shown below.

Figure 5  -- "Size planets comparison" by Lsmpascal - Own work. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Size_planets_comparison.jpg#/media/File:Size_planets_comparison.jpg

Figure 5  — “Size planets comparison” by Lsmpascal – Own work. Licensed under CC BY-SA 3.0 via Commons – https://commons.wikimedia.org/wiki/File:Size_planets_comparison.jpg#/media/File:Size_planets_comparison.jpg

Jupiter and Saturn – and even Neptune and Uranus – really dwarf earth and the other planets and with this visualization I feel it.

Even the simple chart comparing the area of the cross section of the planets gives me a better feel for the data than does the bar chart.

Figure 6 -- Circles comparing cross-section area of the planets.  Yup, I can tell that Jupiter is way bigger than Earth.

Figure 6 — Circles comparing cross-section area of the planets.  Yup, I can tell that Jupiter is way bigger than Earth.

Is it essential that I can tell exactly how much larger one planet is than another?  I don’t think it is and I much prefer the emotional pull of the circles and the spheres.

A Fun Tangent

One thing that’s very hard to express in a static chart is how much space there is between the sun and the planets.  To get a sense of just how incredibly vast the distances are check out this fascinating, albeit somewhat tedious, interactive visualization from Josh Worth.

Getting an emotional wallop with waffles

A few weeks ago Cole Nussbaumer posted a tweet asking people what they thought of this chart from The Economist:

Figure 7 – A waffle chart from the article "Teens in Syria".  See http://www.economist.com/blogs/graphicdetail/2015/08/daily-chart-6?fsrc=rss.

Figure 7 – A waffle chart from the article “Teens in Syria”.  See http://www.economist.com/blogs/graphicdetail/2015/08/daily-chart-6?fsrc=rss.

The first thing that surprises me about this is that The Economist went with a waffle chart and not a bar chart, like the one below.

Figure 8 -- The type of chart I would have expected to see in The Economist.

Figure 8 — The type of chart I would have expected to see in The Economist.

The second thing that surprised me was that I preferred the waffle chart.  Yes, as Jeffrey Shaffer correctly points out, the dots are so tightly packed that you literally see stars between the circles, but  this can easily be remedied.  The question on my mind is why do I prefer waffles?

My answer is that the having each dot represent one of the 120 people surveyed connected with me in a way that the bar chart did not. Combined with the percentage labels (which are critical to the success of the visualization) the waffle chart hit me hard and it did so without dumbing down the importance of the discussion one bit.

So, are bars charts always boring?

No!  In my next blog post I’ll show you an example of a bar chart embedded inside a “come hither” graphic that

  • attracts and engages
  • does not trivialize an important issue
  • represents the data clearly and accurately

Stay tuned.

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  11 Responses to “Accurate vs. Emotional Comparisons – Sometimes Pies, Bubbles, and Waffles are the Better Choice”

Comments (10) Pingbacks (1)
  1. Great stuff steve, loved your examples and clearly shows that there is a time and place for these chart types.
    The waffle chart example is also very good. Yes the bar probably shows the data better than the waffle and adheres to “best practise” But that chart isnt about the data. Its not about the numbers. The length of the bar encodes the number and you can see which is bigger. But by having the components of the waffle represent people, that turns it from being just data into something much more. It then gives an emotional connection, and that is a powerful thing.

    • Matt,

      I was surprised to find myself preferring this approaches, but these are very particular situations.

      In the case if the pie I really didn’t “feel” something. It was more that it was a quicker read of what was most important. In the other two cases I had more of an emotional connection, but do not know if others will respond the same way (although I suspect many will).

      Steve

  2. Steve,

    You haven’t actually provided any evidence that pie, donut, and waffle charts support “emotional comparisons” better than bar graphs do. What is an emotional comparison? How do you measure a chart’s effectiveness in supporting emotional comparisons? Have you actually conducted research or examined research that has done this?

    • Stephen,

      I’m not suggesting that there is any evidence that the pie, planets, and waffle examples will produce an emotional response in other people. For me, and me only, and for these scenarios only, I prefer the pie and the waffle.

      In the case of the pie chart the word “emotional” is a bit strong as it’s not really stirring up feelings, at least for me. Rather, the pie helps me “get” it immediately as I can instantly see that I have more than three-quarters.

      With the planets, I feel the vastness and with the waffle I feel the isolation and fear.

      Again, this is how I feel and suspect others may as well.

      Steve

      • Steve

        What I’m suggesting is that you are making unfounded assumptions. I’m taking the time to point this out because you are not alone in this. This is a common fallacy that is being promoted by many who write about data visualization. It reminds me of the claim that humans use only 10% of their brains, which is nonsense. This began with a single person who made an erroneous claim in the press, followed by countless people who have promoted it since without ever checking its veracity. Until a credible study is done to determine if particular types of graphs evoke particular useful emotions more than others, let’s hold off on making claims that they do.

        I’m not sure that you can even say that your own response to these charts is necessarily emotional in nature. It depends on how we define emotion. Displaying representations of the planets when showing how they vary in size is useful for some purposes because it enables easy recognition of the planets. Is this emotional? I don’t think so. It is informative. The subject matter of the waffle charts involves fear, but not necessarily isolation given the fact that all but one of he charts represent majority groups in Syria. The design of the waffle chart, however, does nothing to convey fear or isolation. I could just as easily claim that a bar graph of the same data conveys fear and isolation.

        • Stephen,

          I don’t think I’m making any unfounded assumptions as I’m just relating the impressions I have with respect to these examples. I’m not claiming that anyone else will have the same impressions that I do.

          I do agree with both you and Jeffrey about whether the word “emotion” is the right word. I certainly don’t feel any emotion with the contrived pie chart example.

          With the planets, however, I am definitely more engaged and get more of a sense of awe than I get with a bar chart. That feeling of awe is emotional and not just informative. But again, that’s just for me.

          As for the Syrian teenagers, I think I chose the words “fear” and “isolation” because I found myself thinking about the 8% that engage in political discussions and social movements. Maybe “alarm” and “concern” would be a more accurate reflection of my feelings. In this case it was the ten filled dots that left a strong impression on me. It was memorable in much the same way I find some of your bricks examples very memorable.

          Will I use a pie chart in my practice? Maybe, if it does no harm. A waffle chart? Very unlikely, but I do think The Economist managed to craft something that was more engaging than a bar chart and did so without obfuscating the facts.

          Steve

  3. Great post Steve. When we build dashboards we aren’t just creating appropriate charts and plunking them down in an orderly, logical fashion. We’re communicating – trying to present a message and help the user ‘get it’ as quickly and easily as possible. Therefore I believe that we need to consider engagement as a factor. These types of charts have their place – if the data warrants and they don’t obfuscate the results – they can communicate the information and engage the user. As you know, I’m a big fan of Kathy Sierra and I love this post on Learning Theory which I think has some helpful ideas for building a dashboard to engage. I especially love the ideas of adding surprise, reducing stress (through simplicity), and ‘don’t underestimate the power of fun’ – which can all be applied to dashboard building.
    http://headrush.typepad.com/creating_passionate_users/2006/01/crash_course_in.html

    • Kelly,

      I responded to Jeffrey about a friend and colleague who has observed that because we live in an era that is information rich but time poor, people value feeling. He further argues that particular aesthetics help convey feeling.

      A particularly daunting challenge is to elicit feeling while also accurately conveying facts.

      I often cite your work as doing this well.

      But…

      I have not yet conducted any research and have no hard evidence that this is the case. Just a feeling.

      Steve

  4. I agree with Stephen Few in respect to “how do we gauge emotional response to a chart?” and “what evidence is there that these chart types increase that?”. There’s likely something here that could be researched more. For example, on Twitter there were a number of people that liked the “dots” because to them those dots represented people more than a bar chart or a number. For me, the dots weren’t any more personal. In general, I don’t really find graphical elements emotional. If the goal is to engage through emotions, then pictures of the teens in Syria would be far more emotional/personal. In addition, Jon Peltier and I both commented that we kick into System 2 (math brain) and start counting or estimating dots. Maybe the title of the blog article would be better described as “When precise quantitative comparisons aren’t needed” rather than emotional vs. not emotional. I agree with you, the image of the planets is great. We see this in a 2D picture but with a beautiful use of shadow we perceive it in 3D and it gives us a nice visual comparison of the size of the planets. A bar chart would give us a much precise comparison, but that’s not needed and the small planets are lost on the bar chart scale too. I also agree that a pie chart with 2 slices doesn’t carry with it the same problems we often see, where people are intending to make good quantitative comparisons with these charts, but instead over slice them and “bling” them up in other ways. You’ve heard me say this before, but the other issue is that the pie chart in your example above and KPI donuts are bounded. There’s only so many votes in congress, so 100% is the max. More often than not, these goals aren’t bounded. Common business measures can exceed goal. The bullet chart allows for this in it’s design while KPI pie/donut is stuck at 100%. Lastly, I agree that we can easily see 25%, 50% and 75% of a pie, but what happens if the vote required is two-thirds? Yes, I can estimate 66% in a pie chart, but if I’m at 64% and 2/3rds is needed then there has to be some sort of precise measure to see how close I am, because while the difference is really small, it’s the difference between passing the bill and not passing the bill. Again, in this case I think a simplified bullet (without performance bands) is a better choice, basically a bar with a target. On a side note, if waffles are used, then at least avoid the scintillating grid and other visual artifacts like starts popping out of the waffle, which is happening in this example.

    • Jeffrey,

      I’ve chatted with a friend and colleague who works for a major healthcare concern. He observes that we live in an era that is information rich and time poor and because people lack time they value feeling. That is, people want to just look at a chart and get a strong feeling from what they are seeing. Aesthetics, he argues, helps convey that feeling.

      As for your comments, I agree with you on almost all points and agree with Stephen Few that I have presented no evidence, just my personal impressions. As for the waffle chart in question — and let’s assume the dots are not so tightly-packed that we see stars — I don’t need to count dots because the numbers are right there for me to see.

      For me, the waffles get me more engaged in the subject and do so without obfuscating the data.

      As for my pie chart example, I purposely chose 75% and not 60% or two-thirds. I maintain that a pie chart will only work well under very narrow constraints.

      I’d love to come up with a way to measure engagement and emotional pull from different chart types and to see if you can elicit feeling without muddying the facts.

      Steve

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