How to calculate percentile ranks

Written by david ferris
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How to calculate percentile ranks
Use percentiles to evaluate test performance. (cholesteral test supplies image by Pix by Marti from

Percentile ranking is a valuable statistical tool with many applications. Percentiles are employed in evaluating standardised tests, measuring group performance and evaluating distribution of wealth across a population. On tests, a percentile is the percentage of scores less than a given score. Percentiles are useful for evaluating things such as test scores because they convert raw data into a simpler form that is easier to understand.

Skill level:

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  1. 1

    Organise the data in numerical order from lowest to highest, where the rank of each datum represents "i." For example, the third-lowest score will be "i3" when plugged into the formula.

  2. 2

    Calculate "n," the number of observations. For example, in a classroom test, it would be the number of test-takers.

  3. 3

    Compute percentile using the formula P = (100(i - 0.5))/n, where "i" equals the rank from Step 1 and "n" is the total number of observations. For example, on a seven-person test, to figure out the percentile for the third-lowest score, you would calculate (100(3-.5))/7, which equals 35.7, or the 35.7 percentile.

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