How it is calculated
The standard deviation must be greater than zero. The calculator does not test whether your data are normally distributed.
z = (x − μ) / σ
Where the numbers come from
- Value
- Mean
- Standard deviation
Example
A value of 110 with a mean of 100 and a deviation of 10 gives z = 1.
Questions
What does z = 0 mean?
The value matched the mean.
Is this a probability?
No. Turning a z-score into a share of the observations also needs a distribution.
Can the deviation be negative?
No. Spread is entered as a positive number. The sign belongs to the z-score.