- A histogram displays the frequency of either continuous or grouped discrete data in the form of bars.
- The bars are joined together.
- The bars can be of varying width.
- The frequency of the data is represented by the area of the bar and not the height.
- When class intervals are different, it is the area of the bar which represents the frequency, not the height.
- Instead of frequency being plotted on the vertical axis, frequency density is plotted.
- Class width = Interval
- Frequency density = Height
- Frequency = Class width × Frequency density
- is the middle value when the data has been written in ascending or descending order.
- For an even number of values: add the two numbers in the middle and divide by 2.
- Mode: is the most frequently occurring value
- Range: is the difference between the highest and lowest values.
- Estimated mean of grouped data:
- Work out the midpoints of each group and multiply by the frequency.
- Then divide by the number of values.
- Cumulative frequency is the total frequency up to a given point.
- Inter-quartile range = upper quartile – lower quartile.