z
score
the standardized score that results from applying a z-score transformation to raw data. For purposes of comparison, the data set is converted into one having a distribution with a mean of 0 and a standard deviation of 1. For example, consider a person who scored 30 on a 40-item test having a mean of 25 and standard deviation of 5, and 40 on an 80-item test having a mean of 50 and a standard deviation of 10. The resulting z scores would be +1.0 and –1.0, respectively. Thus, the individual performed better on the first test, on which he or she was one standard deviation above the mean, than on the second test, on which he or she was one standard deviation below the mean.