P-value Calculator
Calculate statistical significance for Z-test, T-test, Chi-square test, and F-test. Get accurate p-values with visual distribution graphs.
About Z-test
The Z-test is used when data follows a normal distribution, and population variance is known. It's commonly used for large sample sizes (n > 30).
Results
Frequently Asked Questions
What is a P-value?
A p-value is the probability of obtaining test results at least as extreme as the observed results, assuming the null hypothesis is true. A smaller p-value indicates stronger evidence against the null hypothesis.
How do I interpret the P-value?
Typically, p-values are compared to a significance level (α) of 0.05. If p ≤ α, reject the null hypothesis. If p > α, fail to reject the null hypothesis.
What's the difference between one-tailed and two-tailed tests?
One-tailed tests check for significance in one direction (greater than or less than), while two-tailed tests check in both directions (not equal to). Two-tailed tests are more conservative.
When should I use a Z-test vs a T-test?
Use a Z-test when population variance is known and sample size is large (n ≥ 30). Use a T-test when population variance is unknown and sample size is small (n < 30).