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Data & Analytics · Intermediate

Z-Score

The number of standard deviations a value lies from the mean: z = (x - μ) / σ.

Definition

Z-scores standardize values for comparison across scales, find probabilities using the standard normal table and flag outliers (often |z| > 3).

Example

A score of 85 with mean 70 and SD 5 has z = 3.

Exam tip

A negative z-score means the value is below the mean.

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