Definition of Quartile
A quartile is a statistic describing how a set of data points are divided into 4 groups. Quartiles split a set of data by using 3 points: the lower quartile (Q1), the median (Q2), and the upper quartile (Q3). Together with the minimum and maximum values, 3 quartiles split the data set into 4 equal groups:
- 1st group: from the minimum to the lower quartile (Q1)
- 2nd group: from Q1 up to the median (Q2)
- 3rd group: from the median (Q2) to the upper quartile (Q3)
- 4th Group: from Q3 to the maximum data point.
Rules and steps for finding Quartiles
1. Finding median (also called Q2, second quartile)
The median is the midpoint (or middle value) of a set of numbers. You can find the median by ordering the set of numbers and then finding the middle value in the set. The median is also called the 2nd quartile or Q2.
2. Finding the lower quartile (also called Q1, first quartile)
- Step 1: You can find the lower quartile by putting the set of data in order, then locating the median value.
- Step 2: After finding the median value, you can find the middle value between the minimum and the median.
3. Finding the upper quartile (also called Q3, third quartile)
- Step 1: You can find the upper quartile by putting data points in order, then finding the median value.
- Step 2: After finding the median value, you can find the middle value between the median and the maximum.
Finally, you will get 3 quartile values, 77 (lower quartile, Q1), 81 (median, Q2), and 89 (upper quartile, Q3).