Histograms

A histogram is a type bar chart using intervals on the x -axis, with the modification that the interval sizes are not fixed. The frequencies are defined by the areas of the bars, and the y – axis is not a frequency axis, but a frequency density axis. A histogram is better able to represent data because it can be used where the data is irregularly grouped. The heights of a group of fictitious children are summarised in the table below.

Height Frequency
65 – 75 2
75 – 80 7
80 – 90 21
90 – 105 15
105 – 110 12

We construct a Frequency Density Column, usingobtaining the table

Height Frequency Frequency Density
65 – 75 2 2/10 = 0.2
75 – 80 7 7/5 = 1.4
80 – 90 21 21/10 = 2.1
90 – 105 15 15/15 = 1.0
105 – 110 12 12/5 = 2.4

We can now draw the histogram.

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