Box plots - Higher
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Box plots - Higher
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Explainer Video
Summary
Box plots
In a nutshell
Box plots are a diagram used to show the spread of data and are a useful way of summarising.
Features of a box plot
A box plot shows minimums, maximums and quartiles but does not show exact values. See the example below for drawing each of these features on your own box plot.
Definitions
Box plot feature | Definition | Formula (where n is total frequency) |
Lower quartile (Q1 or LQ) | Value of the way through the data | |
Median (Q2) | Value of the way through the data | |
Upper quartile (Q3 or UQ) | Value of the way through the data | |
Interquartile range (IQR) | Contains middle of the data | Upper quartile minus lower quartile: |
Example 1
Olivia is collecting data about the ages of her friends' siblings. The answers she collects are . The median of these numbers is .
Work out the upper and lower quartiles and the interquartile range.
Lower quartile | Work out the position of Q1: |
Upper quartile | Work out the position of Q3: The th value is the upper quartile: |
Interquartile range | |
Median | |
Drawing a box plot
Drawing a box plot involves using all the quantities worked out in the example above.
procedure
1. | Draw a scale. |
2. | Mark on the LQ, UQ and median and draw a box with a line where the median is. |
3. | Mark on the maximum and minimum and connect to the box with a line. |
Example 2
Using the values calculated in example , draw a box plot to represent the data.
FAQs - Frequently Asked Questions
How to draw a box plot?
To draw a box plot: 1. Draw a scale. 2. Mark on the LQ, UQ and median and draw a box with a line where the median is. 3. Mark on the maximum and minimum and connect to the box with a line.
What is the interquartile range?
The interquartile range contains middle 50% of the data. It is the lower quartile minus upper quartile.
What is a box plot?
Box plots are a diagram used to show the spread of data and are a useful way of summarising.
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