Calculate Z-scores and probabilities with our interactive Z-test calculator. Now with one-click chart copying for easy sharing in documents and presentations.
Z-Score
Probability (area to the left of Z)
One-Tailed Probability (area to the right of Z)
Two-Tailed Probability
The Z-test is a statistical procedure used to determine whether two population means are different when the variances are known and the sample size is large.
The Z-score formula is:
Z = (X - μ) / σ
A Z-score represents the number of standard deviations a data point is from the mean. Positive Z-scores indicate values above the mean, while negative Z-scores indicate values below the mean.
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