Stats - Cumulative Frequency
Pearson Edexcel Mathematics 2022
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Axes of the diagram
What goes on the $x$-axis on a cumulative frequency diagram?
The variable being measured.
What goes on the $y$-axis on a cumulative frequency diagram?
Cumulative frequency.
Purpose and construction
What is the purpose of a cumulative frequency diagram?
It allows you to find estimates for medians, quartiles and percentiles.
Drawing a cumulative frequency diagram is like what other process in stats?
Linear interpolation.
When plotting a cumulative frequency diagram for grouped data, which class boundary should you use for the point on the $x$-axis?
The lower class boundary.
Reading off a quartile
I have a cumulative frequency diagram with a max frequency of 60. I want to find an estimate for the upper quartile. What should I do?
- $60 \div 4, \times 4 = 45$
- Find $45$ on the $y$-axis, draw a straight line to the curve.
- Draw a line from that point on the curve to the $x$-axis and that is the value.
Joining the points
How should you join the points on a cumulative frequency diagram?
With a smooth curve.