The Quartile for Ungrouped Data The Quartiles are the score points which divide a distribution into four equal parts. 25% of the distribution are below the first quartile 50% are below the second quartile, and 75% are below the third quartile. Q1 is called the lower quartile and Q3 is the upper quartile. Q1 < Q2 < Q3 where Q2 is nothing but the median. The difference between Q3 and Q1 is the interquartile range. since the second quartile is equal to the median, the steps in the computation of meidan, by identifying the median class is the same as the steps in identifying the Q1 class and the Q3 class.