How to Calculate Z-Score
What is Z-Score?
A z-score (standard score) measures how many standard deviations a data point is from the mean. Z-scores normalise different datasets to the same scale, enabling comparisons.
Step-by-Step Guide
- 1z = (x − μ) / σ
- 2x is the data point, μ is the mean, σ is the standard deviation
- 3z = 0 means at the mean; z = 1 means one std dev above
Worked Examples
Input
x=85, μ=75, σ=10
Result
z = 1.0
85 is 1 std dev above average
Input
x=60, μ=75, σ=10
Result
z = −1.5
60 is 1.5 std devs below average
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