Percentile

Percentiles are points in the data below which a certain percentile of the data are found.

For example, if 80% of the data are at or below 340, then 340 is said to be in the 80th percentile.

The median is the 50th percentile.

For a list that is rank ordered low to high, the formula for figuring percentile rank is:

PR_{i} = 100 ((R_{i} + .5)/n)

For a list that is rank ordered low to high, the formula for figuring percentile rank is:

PR_{j} = 100 (1-(R_{j} - .5)/n)

So, if a score was ranked 3rd from the top out of 40, the equation would be:

PR = 100 (1-(3-.5)/40 = 93.75 or 94

page revision: 2, last edited: 19 Sep 2008 23:52