Quartiles

Quartiles divide the distribution into four equal groups.

Note: The first quartile, \(Q_1\), is the same as the \(25^\text{th}\) percentile; the second quartile, \(Q_2\), is the same as the \(50^{\text{th}}\) percentile (i.e. the median); and the third quartile, \(Q_3\), corresponds to the \(75^{\text{th}}\) percentile!

Finding Data Values Corresponding to \(Q_1\), \(Q_2\), and \(Q_3\)

Step 1

Arrange the data in order from lowest to highest.

Step 2

Find the median of the data values. This the value of \(Q_2\)

Step 3

Find the median of the data values that fall below \(Q_2\), this is \(Q_1\)

Step 4

Find the median of the data values that fall above \(Q_2\), this is the value of \(Q_3\)