Boring Bar Charts, Made More Boring
Posted by Vovici Blog on Mon, Apr 11, 2011
My recommended best practice for pie charts is to avoid them: people have difficulty comparing and contrasting different amounts of visual area and struggle when comparing items at an angle and at distances from one another.
Instead, use bar charts. Boring, boring bar charts.
Here are my best practices for displaying data with bar charts:
- Expand the axis up to 100% for frequencies – Set the maximum percentage of the axis to 100% for frequency graphs. That way the white space serves a function, illustrating how many respondents aren’t selecting a particular answer. Combining this with the next best practice has the benefit of making it easier for readers to visually compare results across charts, something that can’t be done in the illustration below.
- Anchor scales at 0% – PowerPoint will often automatically adjust a scale when it finds small differences in percentages, setting the minimum along an axis at a percent such as 10% or 20%. Unfortunately, this visually exaggerates the differences between answers (see Q4 below).
- Sort appropriately – For rating scales, show the frequencies of each scale item in the order it was asked: e.g., from “not at all satisfied” to “completely satisfied”. But don’t show choices in the order they were asked for lists of nominal items: instead make it easy for readers to see the relative order of preference by sorting them from most frequent to least frequent.
- Use consistent color schemes – Apply the same color coding for products or categories from slide to slide. Most graphing tools will use a standard palette in a standard order – it requires a bit of manual customization to create this consistency, especially when resorting lists or omitting some items.
- Show values for short choice lists – There’s no need to make readers try to estimate the percent that answered a certain way; if the choice list is not so large as to preclude it, show the value for each choice.
- Eschew 3D effects – You’re not creating exhibits for the new Nintendo 3DS! Avoid 3-dimensional shading as it only serves to obscure comparisons.
It’s hard to make bar charts consistent from slide to slide. Boredom sets in and the analyst starts modifying charts for the sake of doing something different. In fact, Betty Adamou from Nebu commented on my pie chart post making exactly this point: “from one report I've seen recently, it looks like some people put in any old graph for the sake of a bit of variance and not taking into consideration how ‘readable’ the graph is, or even what on earth it's trying to communicate.”
My parting thoughts:
- Educate rather than entertain. Your goal is to convey the data not create amusing, entertaining and misleading graphics.
- Look for opportunities to innovate for other data displays. By all means, develop unique visualizations for contrasting multiple questions, for instance – using variations of quadrant analyses, scatterplots and Venn diagrams. However, when it comes to the straightforward reporting of frequencies consistency is best.
Despite the fact I know this advice won’t land me a speaking slot at the New MR web conference on “New approaches to presenting data”: make those boring old bar charts more boring by using them consistently and systematically. It will make it easier for your readers to process and understand your graphs.