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A survey taken in a large statistics class contained the question: "What's the fastest you have driven a car (in miles per hour)?" The five-number summary for the 87 males surveyed is:
min = 55, Q1 = 95, Median = 110, Q3 = 120, Max = 155
Should the largest observation in this data set be classified as an outlier?
ANSWER:
Good job! The IQR in this case is 120 - 95 = 25. Applying the 1.5(IQR) rule, we find: Q3 + 1.5(IQR) = 120 + 1.5(25) = 157.5, and, therefore, the largest observation, 155, should NOT be classified as an outlier. Note, however that in this case: Q1 - 1.5(IQR) = 95 - 1.5(25) = 57.5, and, therefore, the smallest observation, 55, should be classified as an outlier.