Multiple histograms
Histograms can be drawn above a common axis to compare the distributions of a variable in two or more groups. If colour is used, they might be superimposed on each other.
When group sizes differ, relative frequency histograms make comparisons easier.
Pull strength of soldered pins
Population pyramids
To compare two groups, their two histograms can be drawn back-to-back against a common axis. When used to compare age distributions of males and females in a population, these are called population pyramids.
New Zealanders of European and Maori descent in 1989