Histograms

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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

22

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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