p-Value Calculator
Calculate p-value from z-score, t-statistic, or chi-square statistic.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Select the type of test statistic (z, t, or chi-square), enter the value, set degrees of freedom if needed (for t and chi-square), and choose one-tailed or two-tailed. The calculator returns the p-value instantly.
About This Calculator
The p-value is the probability of observing a test statistic as extreme as (or more extreme than) the one calculated, assuming the null hypothesis is true. A small p-value (typically < 0.05) provides evidence against the null hypothesis. The p-value does not measure the probability that the null hypothesis is true.
Frequently Asked Questions
What does a p-value of 0.03 mean?
It means there is a 3% probability of obtaining a result at least as extreme as the observed one if the null hypothesis were true. At the 5% significance level, this would be considered statistically significant.
What is the difference between one-tailed and two-tailed?
A two-tailed test checks for effects in both directions (greater or lesser). A one-tailed test only checks one direction. Two-tailed p-values are double the one-tailed value for symmetric distributions.
Is a p-value of 0.05 always the right threshold?
No. The 0.05 threshold is a convention, not a universal rule. Some fields use 0.01 or 0.001. The appropriate threshold depends on the consequences of errors and the context of the study.