1 and 2 are the first quartile, or Q1 3 and 4 are the second quartile, or Q2 5 and 6 are the third quartile, or Q3 7 and 8 are the fourth quartile, or Q4
Even number of data example (Set A): 4 7 9 11 12 20 Odd number of data example (Set B): 5 8 10 10 15 18 23
Even example (Set A), in which the midpoint lies between 9 and 11: 4 7 9 | 11 12 20 Odd example (Set B), in which (10) is the midpoint: 5 8 10 (10) 15 18 23
Even example (Set A): Median of lower half = 7 (Q1) Median of upper half = 12 (Q3) Odd example (Set B): Median of lower half = 8 (Q1) Median of upper half = 18 (Q3)
Even example (Set A): 12 - 7 = 5 Odd example (Set B): 18 - 8 = 10
