A standard score is an individual score that has been transformed into a number that shows a person's relative status in a distribution of means. To convert an individual score to a standard score, the distance (deviation) of the individual score from its mean (i.e., the average score of the distribution) is computed, and that distance is converted into the number of standard deviations (i.e., the square root of the average squared distance of a set of scores from their mean) that score falls above or below the mean.

Although many different kinds of standard scores have been developed, the ones used most frequently are called Z-scores and T-scores. If the length of an imaginary yardstick is used to define a standard deviation, then that yardstick ...