P-Value Calculator
Calculate p-value from test statistic and degrees of freedom.
Test Parameters
t-value, z-value, or other test statistic
Degrees of freedom (df)
Select one-tailed or two-tailed test
P-Value Result
P-Value
0.0314
two-tailed
Interpretation
Significant (p < 0.05)
Test Parameters:
Test Statistic: 2.5
Degrees of Freedom: 10
Test Type: two-tailed
About This Calculator
The P-Value Calculator helps you calculate the p-value from a test statistic and degrees of freedom. The p-value is the probability of observing a test statistic as extreme as, or more extreme than, the observed value under the null hypothesis.
P-values are used in statistical hypothesis testing to determine statistical significance. A smaller p-value provides stronger evidence against the null hypothesis. This calculator supports both one-tailed and two-tailed tests.
Note: P-values are computed from the Student's t-distribution. Enter a z-statistic with a large degrees-of-freedom value to approximate the normal distribution.
Formula & Calculation Method
P-Value Calculation:
One-Tailed Test:
p = P(T ≥ |t|) or P(T ≤ -|t|)
Two-Tailed Test:
p = 2 × P(T ≥ |t|)
Where:
T = test statistic (t, z, etc.)
df = degrees of freedom
P = probability from distribution
The p-value is calculated from the appropriate statistical distribution (t-distribution, normal distribution, etc.) based on the test statistic and degrees of freedom. Smaller p-values indicate stronger evidence against the null hypothesis.
How to Use This Calculator
- Enter Test Statistic: Input your calculated test statistic (t-value, z-value, etc.).
- Enter Degrees of Freedom: Input the degrees of freedom for your test.
- Select Test Type: Choose one-tailed or two-tailed test.
- View Results: See the p-value and interpretation of statistical significance.
Frequently Asked Questions
What is a p-value?
A p-value is the probability of observing a test statistic as extreme as, or more extreme than, the observed value, assuming the null hypothesis is true. It measures the strength of evidence against the null hypothesis.
What does a p-value less than 0.05 mean?
A p-value less than 0.05 is typically considered statistically significant, meaning there is less than a 5% chance of observing such an extreme result if the null hypothesis were true. This provides evidence to reject the null hypothesis.
What is the difference between one-tailed and two-tailed tests?
A one-tailed test tests for an effect in one direction (greater than or less than). A two-tailed test tests for an effect in either direction. Two-tailed tests are more conservative and require a larger test statistic to achieve significance.
Can I use this calculator for all statistical tests?
This calculator computes exact p-values from the Student's t-distribution, which covers t-tests directly. For a z-test, enter a large degrees-of-freedom value to approximate the normal distribution. For other distributions (chi-square, F, etc.), use a dedicated calculator or statistical software.
Calculator by
NumCalculators Editorial Team
Multi-disciplinary Expert Team