Lecture 10 - Outliers and Test Selection

Question 1

step 1:

Answer 1

• Place data in rank order, e.g.
  
  • 3, 5, 5, 7, 10, 10, 11, 11, 35

Question 2

Step 2:

Answer 2

-Work out the median position (as before - middle value when data is placed in rank order)
- Median position = 5
- Median score = 10

Question 3

Step 3:

Answer 3

• Work out the lower quartile: (median position + 1)/2 = 3rd position, This corresponds to lower quartile score of 5
• When working out the lower quartile position you ignore any fractional component of the median position. (e.g., 4.5 = 4)

Question 4

Step 4:

Answer 4

Work out the upper quartile (N + 1 – lower quartile position). The upper quartile position is 7 which = a score of 11

Question 5

Step 5:

Answer 5

Work out the inter-quartile range (IQR)
= upper quartile score – lower quartile score = 11-5 = 6

Question 6

Step 6:

Answer 6

Work out the length of the whiskers = 1.5 x IQR = 1.5 x 6 = 9

Any point more than 2 whiskers beyond the nearest “hinge” is considered an outlier.