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Z-score
Explanations > Social Research > Statistical principles > Z-score Description | Example | Discussion | See also
DescriptionThus z is a measure of how far away a measurement is from the mean, measured in standard deviations. Calculation: z = (X - X-bar)/S Where X is a measured value, X-bar is the mean of all measured values and S is the standard deviation of all measured values. ExampleJohn gets a mark of 64 in a physics Jane gets a mark of 74 in a chemistry test, where the mean is
58 and the John's z = (64 - 50) / 8 = 1.75 Jane's z = (74 - 58) / 10 = 1.6 Although Jane's score is higher, John's score is further above the mean, and it might be concluded that John has achieved greater success. DiscussionThe z-score provides a simple measure by which different measures can be compared in terms of their deviation from the mean. This is often called standardization. The z-score in use generally assumes parametric data. See also |
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