Pub. date: 2008 | Online Pub. Date: November 27, 2007 | DOI: 10.4135/9781412953948 | Print ISBN: 9781412928168 | Online ISBN: 9781412953948| Publisher:SAGE Publications, Inc.About this encyclopedia
Stacie Ezelle Taylor
Z scores are also called standard units or standard scores. A z score standardizes values of a random variable from a normal (or presumed normal) distribution for comparison with known probabilities in a standard normal probability distribution table or z table. A z score is unitless and is simply a measure of the number of standard deviations a value is from the mean. The z score is especially useful to indicate where a particular data point is relative to the rest of the data. A positive z score indicates that the point is above the mean, while a negative z score indicates that the point is below the mean. The z score removes varying units (e.g., pounds or kilograms) and allows for easy determination of whether a particular result is unusual. Most significance testing, hypothesis ...