Cumulative Frequency and Box Plot

The most important thing to remember here is that when you are drawing a cumulative frequency diagram that you plot the values against the upper bound of each group.

The median is the middle value in the data. So if you have data for 60 people it will be at the 30th person.

The lower quartile (LQ) is a quarter of the way through the data and upper quartile (UQ) is three quarters of the way through.

So if you have data for 60 people the LQ is found at the 15th person and the UQ at the 45 person.

The inter-quartile range (IQR) is found by subtracting the LQ from the UQ

IQR = UQ - LQ

This is an example of a box plot and shows you what each of the bars are.