P-Value Calculator
Z-Test P-Value
Calculate p-value from a z-score (standard normal distribution)
T-Test P-Value
Calculate p-value from a t-statistic and degrees of freedom
Chi-Square P-Value
Calculate p-value from a chi-square statistic and degrees of freedom
Formula
Z-test: p = 2(1 - Φ(|z|)) | T-test: p = 2·P(T > |t|, df) | Chi-square: p = 1 - F(χ², df)
Frequently Asked Questions
What is a p-value?
A p-value is the probability of observing a test statistic at least as extreme as the one computed, assuming the null hypothesis is true. A small p-value (typically < 0.05) indicates strong evidence against the null hypothesis.
What is the difference between one-tailed and two-tailed tests?
A two-tailed test checks for any significant difference (greater or less), while a one-tailed test checks for a difference in a specific direction. Two-tailed p-values are twice the one-tailed p-value.
When should I use a z-test vs a t-test?
Use a z-test when the population standard deviation is known or the sample size is large (n > 30). Use a t-test when the population standard deviation is unknown and the sample size is small.
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