posted by Denim on .
How do I Find the first and third quartiles, Q1 and Q3, of the following set of numbers?
order the data:
Quartile I ends at 8
The quartile II ends at 9.
quartile III ends at 13
The calculation of the quartiles is sometimes not quite clear (especially if the number of observations of a sample is not divisible by four). We therefore provide exact instructions how to calculate the quartiles. Assuming a sample of N observations the quartiles are defined as follows ("round" stands for the rounding to the nearest integer):
1. quartile: the value of the sorted series of observations having the position x = round(0.25*(N+1))
2. quartile (median): if N is even, Q2 is the mean of the two values at the positions N/2 and N/2+1; if N is odd, Q2 is the value at the position (N+1)/2
3. quartile: the value of the sorted series having the position x = round(0.75*(N+1))