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A z-score is how many standard deviations a value sits from the mean: z = (x − μ) ÷ σ. We also give the percentile (area to the left under the normal curve).
Run the rest of your analysis with our other free stats tools.
The number of standard deviations a value is from the mean.
From the normal cumulative distribution of the z-score.
Yes — below the mean gives a negative z.
The percentile assumes a normal distribution.