JoVE Core

Analytical Chemistry

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1.8 : Introduction to z Scores

A z score (or standardized value) is measured in units of the standard deviation. It indicates how many standard deviations the value x is above (to the right of) or below (to the left of) the mean, μ. Values of x that are larger than the mean have positive z scores, and values of x that are smaller than the mean have negative z scores. If x equals the mean, then x has a zero z score. It is important to note that the mean of the z scores is zero, and the standard deviation is one.

z scores help find outliers or unusual values in any data distribution. According to the range rule of thumb, outliers or unusual values have z scores less than -2 or greater than +2.

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