Skewness and outliersEdexcel International A Level Maths: Flashcards

What these 13 flashcards ask

What is positive skew?
What is negative skew?
How do you test skewness using quartiles?
What do you conclude if Q3-Q2=Q2-Q1?
What is an outlier?
Where is the rule for outliers found in an exam question?
Outlier rule using the IQR?
Outlier rule using standard deviations?
Where does a whisker end when there are outliers?
How is an outlier shown on a box plot?
Which measure of location is least affected by outliers?
Which measure of spread is most affected by an outlier?
Why does the standard deviation drop a lot when outliers are removed?

Exam questions on Skewness and outliers

The ages of customers at a shop have lower quartile 24 years, median 28 years and upper quartile 40 years. A value is classed as an outlier if it is more than $1.5\times IQR$ above the upper quartile or more than $1.5\times IQR$ below the lower quartile.
The two oldest customers are aged 62 and 71. Determine which of these ages are outliers.2 marks
The numbers of text messages sent in one day by a sample of students have mode 8, median 10 and mean 12.
Explain why the median is a more suitable measure of location than the mean for these data.2 marks
The daily rainfall, in mm, at a weather station over 15 days has smallest value 0, lower quartile 2, median 5, upper quartile 11 and largest value 40. The next largest value is 19. A value is classed as an outlier if it is more than $1.5\times IQR$ above the upper quartile or more than $1.5\times IQR$ below the lower quartile.
Show that 40 mm is an outlier, and determine whether 19 mm is an outlier.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).