Cumilative Frequency Graphs

Question 1

What is a cumulative frequency graph?

Answer 1

Useful when representing or analysing the distribution of large grouped data sets. They can be used to find estimates if medians, quartiles and percentiles

Question 2

What do cumulative frequency graphs look like?

Answer 2

CF graphs are plotted with the variable on the x axis and CF on the y axis.
CF is the running total of all the frequencies.
They are S shaped and always have a positive gradient.

Question 3

How do you plot a cumulative frequency graph?

Answer 3

1. Calculate the Cumulative frequencies as a column. Add the column to the table. The frequencies are calculated as a running total.
2. Draw your x and y axis of your graph
3. Plot the values as a set of coordinates
4. Join with a curve
5. Add title and label axis

Question 4

How do you find the median using CF?

Answer 4

Half the total frequency (n/2)

Question 5

How do you find the lower quartile using CF?

Answer 5

Quarter of total frequency (n/4)

Question 6

How do you find the upper quartile using CF?

Answer 6

Find a quarter of the total frequency and multiply by 3 (n/4 x 3)

Question 7

What’s an advantage of using CF graphs?

Answer 7

You can easily get data through estimation, you don’t need a table of data

Question 8

What’s a disadvantage of CF graphs?

Answer 8

Everything is only an estimate, no precise data