VizWorld.com

Lots of us in visualization like to berate Pie Charts, primarily due to their constant abuse and mis-use in mainstream media.  Honestly, how many powerpoint presentations have you sat in with a pie chart showing 15 or 20 slices, most under 5%?  Robert Kosara has a great article up referencing a paper from 1991, “Displaying Proportions and Percentages” in Applied Congnitive Psychology, that analyzes the usability of Pie Charts compared to Tables and Horizontal Bar charts, and finds them not just acceptable but in fact better (under a very specific set of circumstances).

While it is not surprising that the table doesn’t do too well in the more complex tasks (adding up numbers is more difficult than combining areas), the comparatively bad performance of the bar chart is. They did not include the stacked bar chart here for some reason, which presumably would have done better than the regular one.

In their discussion, they mention that adjacent segments in a pie chart are especially easy to combine, whereas the same is not true for a bar chart. And that, I think, is an important point: if we step away from the focus on accuracy in reading numbers, some of the more complex tasks are actually easier to do with the pie chart. The bar chart is great for reading and comparing individual numbers, but when it comes to adding up bars, it’s a lot less effective.

via In Defense of Pie Charts | eagereyes.

Science piechart, psychology

Robert Kosara returns with a great writeup on the pro’s and con’s of Pie charts, including some great science in human perception on how we analyze and understand them, as well as a great short-list of reasons why to use and to avoid them.

There are two features that let us read the values on a pie chart: the angle a slice covers (compared to the full circle), and the area of a slice (compared to the entire disk). Research suggests that we look at the angle in the center, essentially reducing the chart to just the crossing lines there. We are not very good at measuring angles, but we recognize 90º and 180º angles with very high precision. Slices that cover half or a quarter of the circle will therefore stand out. Others can be compared with some success, but reading actual numbers from a pie chart is next to impossible.

via Understanding Pie Charts | EagerEyes.org.

Science piechart, visualization

Edward Tufte has long hated pie-charts, for both their aesthetic failings and misleading representations of visual data.  Neal Levene backs up the argument with a new post on Simple Complexity that quite simply shows that Pie Charts are just plain harder to deal with than their counterparts.

Can you rank the size of the wedges from largest to smallest? Take a second to write down your answer. (We will reveal the answer later in the article.) When you are finished, click to the next page of this post.

via Effectiveness of Chart Design — InnovaTech, Inc.’s Simple Complexity.

Science piechart, tufte, visualization