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Quick, exact answers for the three numbers you reach for most. Everything runs in your browser — no sign-up, no upload, nothing leaves your machine.
Get a one- or two-tailed p-value from a z, t, or chi-square statistic.
How many observations per group to detect a difference at a given power.
Cohen's d from two groups' means, SDs, and sizes — with interpretation.
A calculator needs you to compute the statistic first. Stratum starts from your raw data — load a CSV and the t-tests, ANOVA, correlation, regression, and the charts to match all compute themselves.
Stratum