Next, find Q. Recall that the first quartile, Q, is the median of the lower half of the data. That is, the median of the data located below the Q position. Consider the ordered list of data values. The median, Q, which was determined in the last step, has been underlined for clarity. 5, 8, 8, 9, 10, 10, 11, 12, 13 There are nine values in the whole data set, but there are only median of these values. xvalues to the left of the underlined median. The first quartile, Q, will be equal to the Since the lower half of the data has an even number of data values, we will now use the rule to find the median of an even number of data values. sum of middle two values median = 2 The middle two values of the lower half of the data set are 8 and Now, calculate the first quartile. Q. x 8 + = 2 2