Statistics
Distance ignoring direction
How unusual the value is, regardless of whether it sits above or below the mean.
The Formula
|z| = |x - mean| / SD
How unusual the value is, regardless of whether it sits above or below the mean.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| |z| | Absolute number of standard deviations | dimensionless | The quantity most outlier rules are actually built on. |
What Each Symbol Means
|z|dimensionless
Absolute number of standard deviations
The quantity most outlier rules are actually built on.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate a z-score page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate A Z-Score, filed under Math. Every number the guide produces comes from substituting into this one line.