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Jun 23, 2011

How to Make Tornado Charts in JMP

During the Discovery 2008 conference, I heard a number of requests for tornado charts. Later, I realized a tornado chart is basically a horizontal, stacked bar chart with one negative variable and one positive variable, which is something JMP 7 can already handle. They're also called back-to-back charts, comparative histograms and population pyramids. Here's an example showing US population by age group:

tornado chart of population by age and sex

Steps for creating this kind of plot in JMP:

  • Make sure there are two X variables (age and sex) and one Y variable (population). Tables Summary or Stack may be required to get the data in this form.

  • Make every other Y value negative (the females in the example).

  • Launch Chart with the two Xs and one Y and Horizontal orientation turned on.

  • Turn on Stack Bars within Chart.

  • Hide the divider lines by setting their color to off-white in Customize in the right-click menu.

  • Use the Grabber (hand) tool to move the legend into the graph.

  • So now that we can make tornado charts, what good are they? What kinds of data are they best for? How is the above tornado chart better or worse than the normal side-by-side bar chart (below)? Tell us what you think.

    bar chart of population by age and sex

    Community Member

    Doug Okamoto wrote:

    The baby boom echo includes the 15-19 year old age group, too.

    Community Member

    Doug Okamoto wrote:

    The tornado chart (Figure 1) gets my vote over the side-by-side bar chart. Here's why.Interpretation of the Age-Sex Distribution from Population Pyramid (Figure 1)

    In US Census 2000, the largest 5-year age group was 35-to-39 year olds with 22.7 million people (11.3M males, 11. 4M females), representing 8.1 percent of the total population. The second largest five-year age group was 40-to-44 year olds with 22.4 million people (11.1M males, 11.3M females), representing 8.0 percent of the population. The relatively large number in these two age groups is represented in Figure 1 by bulges in the population pyramid. People in these two age groups were primarily born during the post-World War II "baby boom" (those born from 1946 through 1964). In Census 2000, the baby-boom cohort was age 36 to 54 and represented 28 percent of the total U.S. population. The offspring of these baby-boomers or â baby boom echoâ cohort can be seen in the bulges of 10-10.5M for males and females in the 5-to-9 and 10-14 year old age groups in Figure 1.

    Source Data Set: Census 2000 Summary File 1 (SF 1) 100-Percent Data

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