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Statistics

P-Value Calculator

Convert a z or t statistic into a one-sided or two-sided p-value with an explicit alternative hypothesis.

Data stays on this deviceConvention explained below
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Check the dataset and sample convention before interpreting results.

See the method

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Your result

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Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter reference distribution, test statistic, degrees of freedom (t only), alternative hypothesis, significance level.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

Use the selected reference distribution to find the probability in the tail specified by the alternative. Two-sided probability doubles the tail beyond the absolute statistic.

A WORKED EXAMPLE

Using reference distribution = t, test statistic = 2, degrees of freedom (t only) = 20, alternative hypothesis = two, significance level = 0.05, the result is 0.0592655354 probability. Change these example inputs to match your task; use the method above to check each step.

What to keep in mind

The entered statistic must already be standardized under the null model. This tool does not validate the study design. A descriptive or probability calculation under the stated assumptions. Check the sample design and model before interpreting results.

Reference: NIST: statistical methods handbook

Common questions

Should I choose a one-sided or two-sided test?

Use two-sided when departures in either direction matter. Use a one-sided alternative only if its direction was chosen before seeing the data. Switching tails after inspecting a result changes the test.

Where do I get the test statistic?

A z or t statistic comes from a specified statistical test, not from a raw observation. Use the linked one-sample, paired or independent-sample test when you have observations rather than a standardized statistic.

Methodology maintained by ClarityKit. How these tools are built and checked.