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, using
obtaining 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.
