Percentile rank

The percentage of scores in a reference group that fall at or below a given score.

A percentile rank tells you what percentage of scores in a reference group fall at or below a given score. A percentile rank of 75 means the score is at or above 75% of the comparison group.

Percentile ranks are intuitive — most people grasp "75th percentile" faster than a raw score or a Z-score — but they have a quirk. Differences in percentile rank are not proportional to differences in the underlying construct. Moving from the 50th to 55th percentile is a small underlying change; moving from the 95th to 99th percentile is a much larger one. Most score distributions are bunched near the middle.

Norms — Reference distributions of scores from a defined population, used to interpret an individual's score in context.
Raw score — The direct, untransformed score from an assessment — typically the sum of item responses.
Z-score — A standardized score expressing how many standard deviations a raw score is from the mean.
T-score — A standardized score with a mean of 50 and a standard deviation of 10, commonly used in psychological testing.
Normal distribution — A symmetric, bell-shaped probability distribution that describes how many psychological traits are spread across a population.

Percentile rank

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