P-Value Calculator - Free Statistical Significance Calculator
P-Value Calculator
Calculate p-values from test statistics to determine statistical significance. Supports z-tests, t-tests, chi-square tests, and F-tests.
Z-Test P-Value
Common Critical Values
How to use this calculator
📈 How to Use This Calculator
- Select your test type: Z-test, T-test, Chi-square, or F-test
- Enter your test statistic value
- Provide degrees of freedom (for t, chi-square, and F tests)
- Choose the test direction (one-tailed or two-tailed)
- Click calculate to get the p-value and interpretation
📐 Understanding P-Values
What is a P-Value?
The p-value is the probability of obtaining test results at least as extreme as the observed results, assuming the null hypothesis is true.
Common Significance Levels (α)
- • 0.10: Marginally significant (90% confidence)
- • 0.05: Statistically significant (95% confidence)
- • 0.01: Highly significant (99% confidence)
- • 0.001: Extremely significant (99.9% confidence)
Decision Rule
If p-value ≤ α: Reject the null hypothesis
If p-value > α: Fail to reject the null hypothesis
🌟 Test Types Guide
Z-Test
Used when population standard deviation is known or sample size is large (n > 30)
T-Test
Used for small samples when population standard deviation is unknown
Chi-Square Test
Used for categorical data, goodness of fit, or independence tests
F-Test
Used for comparing variances or in ANOVA
💡 Important Considerations
- • P-values do not measure the size or importance of an effect
- • Statistical significance does not imply practical significance
- • Multiple testing requires adjustment (e.g., Bonferroni correction)
- • Consider confidence intervals alongside p-values
- • Pre-specify your significance level before analysis
- • Report exact p-values rather than just "p < 0.05"
⚠️ Common Misinterpretations
- • P-value is NOT the probability that the null hypothesis is true
- • P-value is NOT the probability of making a Type I error
- • A non-significant result does NOT prove the null hypothesis
- • P = 0.051 is not fundamentally different from P = 0.049
- • Small p-values can occur with trivial effects in large samples
About this calculator
Calculate p-values from test statistics for z-tests, t-tests, chi-square, and F-tests. Determine statistical significance easily.
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