Cumulative Frequency Diagrams (Edexcel IGCSE Maths A)

The cumulative frequency of an item is the total frequency of all items that are less than or equal to the given item.

Cumulative frequency is a running total of the frequencies.

To draw a cumulative frequency diagram:

• For each group, plot the cumulative frequency at the endpoint of the group

• Join the points together with a smooth curve that is always increasing

False.

To draw a cumulative frequency diagram, you do not plot the midpoint of a group against its frequency.

You plot the endpoint of a group against its cumulative frequency.

If the total frequency is 100, you can use a cumulative frequency diagram to estimate the median value.

1. Draw a horizontal line from 50 on the vertical axis to the curve

2. Draw a vertical line down from this point on the curve to the horizontal axis

The value on the horizontal axis is an estimate of the median

To estimate the lower quartile using a cumulative frequency diagram:

1. Divide the total frequency by 4

2. Draw a horizontal line from the result on the vertical axis to the curve

3. Draw a vertical line down from this point to the axis

The number on the horizontal axis is an estimate for the lower quartile