The z-score is the number of standard deviations a control result is from the expected mean. Use the following formula to calculate the z-score:

A z-score of 2.3 indicates the observed value is 2.3SD away from the expected mean. A data point with this z-score violates the 1_{2s} rule, but not the 1_{3s} rule. The z-score appears on the **Single Test Point Data Entry** dialog box.

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