Statistics 1 Revision Notes - Mr Barton Maths

⇒
Q 1 = 4⋅5 + 5 ×
= 7⋅7421875…= 7⋅74 to 3 S.F.
Q 2 and Q 3 can be found in a similar way.
Percentiles
Percentiles are calculated in exactly the same way as quartiles.
Example: For the 90 th percentile, find and proceed as above.
Box Plots
In a group of people the youngest is 21 and the oldest is 52. The quartiles are 32 and 45,
and the median age is 41.
We can illustrate this information with a box plot as below – remember to include a scale.
lowest
value
Q 1 Q 2
Q 3
highest
value
20 30 40 50
age
Outliers
An outlier is an extreme value. You are not required to remember how to find an outlier – you
will always be given a rule.
Example: The ages of 11 children are given below.
age 3 6 12 12 13 14 14 15 17 21 26
Q 1 = 12, Q 2 = 14 and Q 3 = 17.
Outliers are values outside the range Q 1 – 1⋅5 × (Q 3 – Q 1 ) to Q 3 + 1⋅5 × (Q 3 – Q 1 ).
Find any outliers, and draw a box plot.
14/04/2013 Statistics 1 SDB 17