The upper quartile Q 3 is the median of the upper half of the data. The third quartile can be measured as the middle value between the median and highest values of the data set. To find the median value or the value that is half way along the list the method is to count the number of numbers add one and divide by 2.
The first quartile or lower quartile is the value that cuts off the first 25 of the data when it is sorted in ascending order.
One definition of the lower quartile is the middle number between the smallest number and the median of the data set. The values that divide a list of numbers into quarters. Quartile 1 Q1 442 4. 2nd quartile Q2 is the median of data.