Figure 1. Example of a dual histogram
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A popular graph in demography is a population pyramid, which can be defined as shown in the box below.
| population pyramid "diagram designed to show the comparison of a human population by sex and age at a given time, consisting of a pair of histograms, one for each sex, laid on their sides with a common base" (Everitt, 2004, p. 292) |
However this does not only apply well for demographic variables, it can also be used for any scale variable that you want to compare between two groups (Dallal & Finseth, 1977). The term dual histogram is therefor used although you might also come across the term pyramid histogram, two-way histogram, or back-to-back histogram.
| dual histogram diagram that shows a histogram, split into two groups, placed back to back |
An example of a dual histogram is shown in Figure 1.
Figure 1. Example of a dual histogram