# Cumulative frequency graphs

## Presentation on theme: "Cumulative frequency graphs"— Presentation transcript:

Cumulative frequency graphs
How to draw and use….. Cumulative frequency graphs

Cumulative frequency is just…
A running total

Look at these tables Age, a (years) 3 9 17 10 5 Age, a (years) ≤ 12 3
Frequency 5 < a ≤ 12 3 12 < a ≤ 20 9 20 < a ≤ 30 17 30 < a ≤ 40 10 40 < a ≤ 60 5 Age, a (years) Cumulative frequency ≤ 12 3 ≤ 20 12 (3+9) ≤ 30 29 (3+9+17) ≤ 40 39 ( ) ≤ 60 44 ( )

Once we have calculated the cumulative frequency
We don’t need the frequency any more.

We can use our results to draw a cumulative frequency curve
Age, a (years) Cumulative frequency ≤ 12 7 ≤ 20 19 ≤ 30 36 ≤ 40 42 ≤ 60 44 Along the ‘x’ axis Up the ‘y’ axis

Plot the points 44 40 36 32 28 24 Cumulative 20 frequency 16 12 8 4
Cumulative frequency Age (years)

Draw the curve 44 40 36 32 28 24 Cumulative 20 frequency 16 12 8 4
Cumulative frequency Age (years)

Now draw in the median Remember it is halfway up the cumulative frequency axis – in this case 22

Median…… 44 40 36 32 28 24 20 16 12 8 4 Cumulative frequency
Cumulative frequency halfway up Read off here Age (years)

The median is …….. (about) 26.

Now for the lower quartile
Quarter of the way up the Cumulative frequency axis

Lower Quartile 44 40 36 32 28 11 – quarter of 44 24 Cumulative 20
16 12 8 4 11 – quarter of 44 Cumulative frequency Read off here Age (years)

So the lower quartile is ….
19

Three quarters of the way up the Cumulative frequency axis
Upper quartile Three quarters of the way up the Cumulative frequency axis

Upper quartile 33 – three quarters of 44 44 40 36 32 28 24 Cumulative
20 16 12 8 4 Cumulative frequency Read off here Age (years)

The upper quartile is …. 32

Upper quartile – lower quartile
Inter-Quartile range Upper quartile – lower quartile

Upper quartile – lower quartile

Inter-quartile range =
13

Try this one ….. 9 18 23 6 3 1 Salary (£) 10000 9 14000 27 18000 50
Frequency 9 18 23 6 3 1 Salary (£) Cum. Freq. 10000 9 14000 27 18000 50 20000 56 24000 59 30000 60
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