This deep dive covers Special Cases and Outliers within Box Plots for GCSE Mathematics. Revise Box Plots in Statistics for GCSE Mathematics with 18 exam-style questions and 20 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 9 of 11 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Special Cases and Outliers
Identifying Outliers
An outlier is typically defined as a value that is:
- More than 1.5 × IQR below Q1
- More than 1.5 × IQR above Q3
Lower fence: 20 - (1.5 × 20) = 20 - 30 = -10
Upper fence: 40 + (1.5 × 20) = 40 + 30 = 70
Outliers: Any values below -10 or above 70
Modified Box Plots
When outliers are present:
- Calculate outlier boundaries
- Draw whiskers to the last non-outlier values
- Plot outliers as separate points
Practice questions for Box Plots
On a box plot, what does the box (the rectangle) represent?
Two athletics clubs record the 100m sprint times (in seconds) for their members. The five-number summaries are shown below. Club A: Min = 11.2, Q1 = 12.4, Median = 13.1, Q3 = 14.2, Max = 16.5 Club B: Min = 12.0, Q1 = 13.5, Median = 14.8, Q3 = 16.1, Max = 17.3 Compare the distributions of sprint times for the two clubs. You must use the data to support your answer. (3 marks)