From the monthly archives:

October 2009

Is Data Visualization Useful? You’ll Have to Prove It.

by Jorge

Great data visualization is hard to measure: you can’t prove you have a good chart. Unless you can convince your employer to deploy at least two different formats/layouts and are able to compare results, you can say “this is a good chart” but that’s an act of faith, not an act of science.

It’s True Because It Rhymes

Information visualization experts like to evaluate a chart based on its compliance to some more or less accepted standards (Tufte’s data-ink ratio, for example). That’s like saying “it must be true because it rhymes”: the truth is defined by the language itself, not by the real world. Now, please close the curtains of our ivory tower…

I know, it’s not easy to assess the efficiency and effectiveness of good displays. They look natural and obvious, undeserving of praise and, probably, boring and uninspiring. Compare these charts:

Bubble charts

This is a true story: users wanted to evaluate sales territories, one at a time. Color-coding each bubble (Example A) was pointless, while Example B provided context without distractions. Guess what chart they would choose if they were allowed to… (happy ending: they reluctantly accepted Example B). (A word of advice: if you are looking for a promotion, a kindergarten chart variety always outperforms a “serious” chart.)

If your chart is doing a good job at helping people, no one will actually be aware of the chart’s role at making sense of the data. That’s why it is so hard to find good examples of data visualization using standard charts. If people actually like them, they like them because of their usability and/or interactive features.

When Stephen Few asks the readers “true stories about the benefits of data visualization” that’s almost an admission of impotence.  He should have hundreds if not thousands of good examples to share with us, right? Well, I know there are many examples out there, but I can give you none, sorry. Is data visualization some kind of astrology? I know it works. Why? Because I have faith. (On second thought, he is not asking for good data visualization examples. It really doesn’t matter if you use Tableau or Xcelsius, and that’s a relief.)

Opening the Pandora Box

Ultimately, what makes a good chart is how it resonates with your audience. Assuming that your are not unethically distorting the data, a chart that forces people to act is better than another one that only makes people aware of the subject.

If a single chart can save the world, it will not be a Few’s or Tufte’s 100% compliant chart. It will be a glossy Xcelsius pie chart.

(Wow, that’s depressing…)

If you read this blog that’s a clear sign of intelligence and sophistication :) . Unfortunately, you are not representative of the typical data visualization user and/or producer. The real world loves pie charts and doesn’t understand scatter plots.

Here is my Pandora box: give the audience what it expects and understands, even if that hurts your data visualization soul (OK, give it 90% of what it expects and use the remaining 10% to educate it.)

Cultural Relativism? Not So Fast.

Please don’t misrepresent these arguments. I’m not saying that all charts are born equal. There is a reference point and some misconceptions should be avoided A chart that maximizes insights, removes clutter, uses color wisely and clearly shows the patterns hidden in vast amounts of data, that’s probably a good chart and that’s what you should aim for. And yes, you should avoid pie charts.

If you present some sophisticated charts to your unsophisticated audience you’ll lose it. Relax. Draw a line but don’t forget the candies. You can take a horse to the water, but you can’t make him drink, unless you give him some sugar cubes…

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Animation, Interaction and Dynamic Excel Charts

by Jorge

If you want to add animation to your charts that’s a clear sign that you have too much free time. Go out and play with the kids instead. :)

Yes, animation is a powerful attention-grabber, even more powerful than a glossy 3D pie chart in Crystal Xcelsius. And yes, it can actually be helpful (from time to time). But.

A good example of animation in data visualization is the famous Hans Rosling’s TED presentation, where a long-term pattern is clearly seen (at min 4:00):

This works well because the trend is easily identifiable and you don’t care much about the details. It would be much more difficult to make sense of this data if there were multiple trends and short-term variability. (More on the use of animated charts.)

After watching this presentation people often ask me: “Wow! Can we do that in Excel?” Wrong question. The right question would be “Wow! Can our data do that?”.

You can always create a simple animation in Excel, but it’s hard for a non-programmer to get a smooth transition effect. Here is an example from my dynamic Excel dashboard:

Although you can see a pattern emerging, you would need to add a complex interpolation routine to make it look better (read Jon’s post to see how a simple interpolation can be used).

Animation is better used if there is a pattern to be discovered, but you need something more: the ability to interact with the data. You must be able to stop, go back, get the details. While you can create a simple animation effect with a for/next loop in VBA, interaction with the chart is much easier using a Google spreadsheet with a motion chart:

(This is just an image. Click here to play with the chart.)

Dynamic Charts in Excel

In Excel, instead of creating a VBA routine, consider using a scroll bar linked to the value you want to change (year, for example):

Using a scroll bar adds some level of interaction because you can scroll back and forth, pause and examine the details for a specific year. Obviously, you need to change the chart data source dynamically.

Let’s recap how to create a dynamic chart in Excel. You can do it by changing values or by changing the data source itself (using a different range).

Option #1: Copying the Data

The range A1:E11 is our data set and we are comparing regions. Moving the scroll bar at the bottom changes the year. Column F is our data source. You can enter this formula there:

=OFFSET($A$1,ROW()-1,MATCH($A$13,$B$1:$E$1,0),1,1)

ROW() gets the current row and MATCH() returns the position of value 2002 (A13) in the range B1:E1. So, the formula in cell F2 reads something like this: start at A1, go down one row, go right three columns and get the data in that cell (range of width 1 and height 1). When the user selects a different year the data is copied to column F.

Option #2: Using a Dynamic Named Range

The second option is to create a dynamic named range. Create a named range and, instead of entering a fixed range, enter this formula:

=OFFSET(Sheet1!$A$1,1,MATCH(Sheet1!$A$13,Sheet1!$B$1:$E$1,0),10,1)

As you can see, it is very similar to the one above, but now the number of rows down is fixed (1) and it returns a range of 10×1 cells (because we have 10 regions, but if the number of regions varies you may use COUNTA(A:A)-1 to count the number of regions, excluding header – and don’t forget to move the year to a different cell…).

When you verify your range this is what you get:

You just need to use this range in your chart (when entering the range you must add the workbook name: “=Book1!SourceData”). You’ll also need a range for the category axis labels:

=OFFSET(Sheet1!$A$1,1,0,10,1)

You can download the spreadsheet here.

Take Aways

If you want to animate your charts make sure you do it because it adds value, not because you want to show off your skills. You can do it in Excel but it looks much better in Rosling’s Trendalyzer or in the Google spreadsheet gadget.

To create animations your data source must change dynamically, and that requires some work (and skills). I advise you to shift your focus from animation to interaction and use all that work to design a better user experience. Do you prefer a “wow!” (animation) or a “wow, thank you!” (interaction that actually helps the user)?

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