Rank and age in a university
This diagram illustrates that the conditional distributions of Y simply rescale the counts for each X to make the total for each X equal 1.0.
Select Rank then Propn within Rank. This dynamically scales the bar charts of Age to make each have the same total. This makes it clearer that:
The age distributions of assistant professors and instructors are very similar, but different from those of associate and full professors.
Select Frequency and Age to show the raw counts, clustered by age. Select Propn within Age to display the conditional distributions of the ranks.
Advanced
You can also use the diagram to discuss the difference between P(X given Y) and P(Y given X). With the bars clustered by Age, select Propn within Age and then Propn within Rank to show these different proportions in bar charts, both clustered by Age. For example, mention that:
The data are taken from a textbook but are probably artificial.