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.