Histograms
What is grouped data?
- You might have lots of different values
- To help summarise the data you can group the data into intervals
- For example: If you are measuring the heights of 1000 adults then you could use the groups:
- Less than 140 cm
- At least 140 cm but less than 160 cm
- At least 160 cm but less than 180 cm
- At least 180 cm
- For example: If you are measuring the heights of 1000 adults then you could use the groups:
What is a histogram?
- A histogram is used when data has been grouped
- For your exam the groups will have equal intervals
- A histogram is similar to a bar chart
- The variable (height, length, etc) is plotted on the horizontal axis
- The frequency is plotted on the vertical axis
- Rectangular bars are drawn
- The width covers the interval of the group on the horizontal axis
- The height is the frequency
- There should be no gaps between the bars of a histogram
- This is different to a bar chart
Worked example
The table below and its corresponding histogram show the mass, in kg, of some new born bottlenose dolphins.
| Mass | Frequency |
| At least 4 kg but less than 8 kg | 4 |
| At least 8 kg but less than 12 kg | 15 |
| At least 12 kg but less than 16 kg | 19 |
| At least 16 kg but less than 20 kg | 10 |
| At least 20 kg but less than 24 kg | 6 |
Draw a frequency histogram to represent the data.
Draw rectangular bars with no gaps.
