Follow-Up on Tornado Charts for Data Visualization
Last week I showed how to make tornado charts in JMP and asked for input on the utility of these types of visualization. Here are thumbnails of the two alternative views of US population by age and sex.
One commenter pointed out that the back-to-back bars of the tornado style chart makes it easier to see the baby boom population bump and the smaller next generation bump 25 years later. While you can also see that general trend in the "normal" chart with side-by-side bars, it's not as obvious (especially the secondary bump) because the alternating gender values add choppiness to the trend curve.
Besides the trend of population versus age, the chart also shows the breakdown of population by gender for each age group. The back-to-back bars are good enough to see major variations, such as the larger proportion of females in the older age groups, but the side-by-side bars are better if you want to highlight smaller variations by gender. In the example, only the side-by-side bars make it clear that males are more common in the younger age groups.
The bottom line is that the appropriate visualization depends on the message you want to communicate.