Quartiles divide a rank-ordered data set into four equal parts. Q1 is the “middle” value in the first half of the rank-ordered data set. Q2 is the median value in the set. Q3 is the “middle” value in the second half of the rank-ordered data set.

A quartile divides data into three points—a lower quartile, median, and upper quartile—to form four groups of the dataset. The second quartile, Q2, is also the median. The upper or third quartile, denoted as Q3, is the central point that lies between the median and the highest number of the distribution.

First Quartile(Q1) = ((n + 1)/4)th Term. Second Quartile(Q2) = ((n + 1)/2)th Term. Third Quartile(Q3) = (3(n + 1)/4)th Term.

Middle Quartile (Q2) = (N+1) * 2 / 4

1. Middle Quartile (Q2) = (19+1) * 2/4.
2. Middle Quartile (Q2) = 40 / 4 = 10th data point.

The median is considered the second quartile (Q2). The interquartile range is the difference between upper and lower quartiles. The semi-interquartile range is half the interquartile range. When the data set is small, it is simple to identify the values of quartiles. Let’s look at an example.

Order your data set from lowest to highest values

To find the lower quartile or the value that is one quarter of the way along the list, count how many numbers there are, add 1 and divide by 4. Lower quartile = = , which is the second value in the list. To find the value of the upper quartile, multiply the lower quartile by 3 as .

To calculate quartile deviation first, arrange the given set of data in ascending order, find the center value and the find out the n/2+1 value. After that consider, first four values Q1 and last four values Q3. Find the median value for Q1 and Q3. At last subtract the value of Q3 with Q1 and divide it by 2.

Click in cell D1. Type “=” and the quartile formula, including the range cells of that contain the data and “1” for the quartile number, to determine the first quartile of the set of data. Press “Enter” after typing. For example, type “=QUARTILE(A1:A8,1)” and press “Enter.”.