To find a

percentile rank all of the numbers in a given set from

largest to

smallest. Then, go along the list of numbers to the number that represents the

percent you are looking for. For example:

In a

set of 100 numbers, the number that is 10% of the way through the

set is the tenth number. The value of this number is the tenth percentile.

Since the number 50% of the way through the set is the middle number and, since the median of a

set is the value of the middle number, the 50th percentile of a set is equal to the

median.

Since the 50th

percentile represents a

percentile divisible by ten it is what is called a

decile. Since it is also divisible by 25 it is also a

quartile.

Percentiles are a

statistical tool used to examine the

spread of a

set.