Histograms
A histogram is a way to graphically display the density of values in a data set.
In a simple histogram, the axis is split into sub-intervals of equal width called classes. A rectangle is drawn above each class with height equal to the number of values in the class — the frequency of the class.
Ages of patients admitted to cardiac unit
A histogram is similarly easy to understand when the class width is a multiple of the width of the dot plot stacks.