How Not to Make a Point

While surfing the web today I came across the image below posted at kissmetrics.com. This is a piece of a much larger graphic, but it makes my point. I don’t care for Pie Charts and this presentation seems to be particularity bad. There are other graphics at the site that are much worst. But this is the one I came across. The theme they use seems to focus on pretty graphic that give a pop. But the visualization seems to take precedence over presentation of the data.

The first problem is that the image shows two dimensional data using both time and percent of the population in each cell. Pie charts do not handle two dimensional numeric data very well. The authors choose to sort the data by the percent of the population and plotted those data points in a clockwise direction around the pie chart. But in doing so they lost the ability to present the time dimension in a meaningful fashion. This is clearly a situation where a simple bar chart would work much better. I could create such a chart but they have not given me the data that makes such an effort worthwhile for they have chosen to use differing time segments in the pie chart. Pie charts work better when the second dimension is a categorical cell where the ordering of the cell is somewhat arbitrary from at least a numerical perspective. But again I would very much prefer to never see a pie chart.

The authors choose to emphasize that 3% of the people are willing to wait less then a second for a page to load. But if we look at the cell for 1 to 5 second wait which comprises 16% of the population it seems to indicate a 3% drop out for each additional second. So the one second dropout rate is hardly surprising. By choosing to use one segment for the under one second group they have make this sliver of the pie chart appear to stand out. Using 20 seconds at the upper cutoff for the charts seems to be premature as well. My preference would be to see a bar chart with five second intervals through at least 25 or 30 seconds with the final cell being 25+ or 30+ seconds.