How to Calculate Percentile Ranks

Use percentiles to evaluate test performance.

Percentile ranking is a valuable statistical tool with many applications. Percentiles are employed in evaluating standardized 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.

Instructions

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

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.

References

• Stanford University: Calculating Percentiles
• Ed Helper: Statistics

Resources

• CNX: Percentiles