Arrange all samples from small to large and divide them into four equal parts. The score of the three dividing points (this is a numerical value) is a quartile. The smallest quartile is called the lower quartile. Of all the values, one quarter is less than the lower quartile and three quarters is greater than the lower quartile. The quartile of the midpoint is the median. The largest quartile is called the upper quartile. Of all the values, three quarters are less than the upper quartile and one quarter is greater than the upper quartile. There are also known as the 25th percentile and the 75th percentile.

Calculation process: first find the median (if there are odd samples, it is the middle number arranged from small to large; If it is an even number of samples, it is the average of the middle two numbers). Then calculate the median from the smallest number to the median (for example, 123456789, the median is 5, and the lower four digits are 1 to 5, which is 3). The middle value of the maximum is the upper quarterback.