MATH 2233 Lecture Notes - Lecture 5: Quartile, Percentile, Box Plot
16 Nov 2017
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Recall that the median m is a special percentile (which?). 2nd quartile or median: q2 = p50 = m. Interpretation: approximately 25% of the sample falls below q1 = 26. 1. 1st quartile: ap(q1) = (25/100)30 = 7. 5 so pos(q1) = 8; thus q1 = 26. 1. 2nd quartile or median : pos(m) = (n + 1)/2 = 31/2 = 15. 5. 3rd quartile: ap(q3) = (75/100)30 = 22. 5 so pos(q3) = 23 ; thus q3 = 27. 4. Quartiles play an important role in another type of display called a boxplot. Ap(m) = (50/100)30 = 15 so pos(m) = 15. 5 m = (26. 6 +26. 7)/2 = 26. 65. Interpretation: approximately 50% of the sample falls below m = 26. 5 m = (26. 6 +26. 7)/2 = 26. 65. Interpretation: approximately 75% of the sample falls below q3 = 27. 4. The boxplot is a graphical display of the quartiles and the extreme values of a sample.
