P Value Calculator

What Is a P Value Calculator?

Why Use Our P Value Calculator?

How to Use It in 3 Steps

P Value Calculator FAQ

How to calculate p value?

Work out the test statistic, then find the probability of a value at least that extreme under the null hypothesis from the statistic’s distribution. Enter the statistic above and the p value calculator does the second step exactly.

What is a p value?

The probability of a result at least as extreme as the one observed if the null hypothesis were true. Small values suggest the data would be unusual if there were no real effect. A p value does not measure how important a result is.

How to interpret p value?

A p value of 0.03 means results this extreme would turn up 3% of the time if there were no effect. It is not the probability that the null hypothesis is true, and it says nothing about how big the effect is.

What p value is significant?

By convention, p below 0.05; some fields use 0.01 or 0.005. Choose the threshold before looking at the data, and report the exact p value either way. A p value just above the line, such as 0.051, is not meaningfully different from one just below it.

How to find p value from t test?

Compute t, then use the t distribution with the test’s degrees of freedom: n − 1 for one sample, or n₁ + n₂ − 2 for two pooled samples. Choose t statistic above, enter t and df, and read p. For a Welch test, use the adjusted degrees of freedom your software reports, which need not be a whole number.

How to find p value chi square?

Use the chi-square distribution with (rows − 1) × (columns − 1) degrees of freedom for a contingency table, or categories − 1 for goodness of fit. The p value is the area to the right of your statistic. The p value calculator handles any number of degrees of freedom from 1 upwards.

What is p value in hypothesis testing?

It is the measure of evidence used to decide whether to reject the null hypothesis: when p is below the chosen significance level α, the result is called statistically significant.

How to find p value from z score?

For a two-tailed test, p = 2 × (1 − Φ(|z|)), where Φ is the standard normal distribution. z = 1.96 gives p = 0.05 and z = 2.58 gives about 0.01. For a one-tailed test, halve those values, provided the effect lies in the predicted direction.

How to find p value for two tailed test?

Double the one-tailed area beyond your statistic. Use two tails unless you stated in advance that only one direction of effect matters. Choose Two-tailed in the p value calculator and it does the doubling for you.

How does p value relate to confidence interval?

They agree: a 95% confidence interval that excludes the null value goes with a two-sided p value below 0.05, and one that includes it with p of 0.05 or more.

How do you write p value?

Write p in italics, give two or three decimals and drop the leading zero, as in p = .032, or write p < .001 for very small values, following APA style.

Can I get a p value from raw data or means?

Compute the test statistic first, for example t = (mean − value) / (sd / √n) for a one-sample test, then enter it here with its degrees of freedom. For two independent samples, divide the difference in means by its standard error instead.

How do I find the p value of a correlation?

Convert r to t = r√(n − 2) / √(1 − r²) with n − 2 degrees of freedom, then enter that t here to get the p value. This matches the p value most statistics packages report for Pearson's r.

How do I adjust p values for multiple comparisons?

The Bonferroni correction multiplies each p value by the number of tests, capping at 1, or equivalently divides α by that number. Holm’s method is less conservative and still controls the error rate. With many tests, false discovery rate methods such as Benjamini–Hochberg are common.

Why is my p value 0?

Software often rounds very small values to 0. A true p value is never exactly zero, so report it as p < .001. This calculator shows tiny values in scientific notation instead.

Can I see how the p value is calculated?

For z, p comes from the standard normal distribution; for t, from Student’s t with your degrees of freedom; for chi-square, from the right tail of the chi-square distribution. The answers above give each formula. All three are computed directly rather than looked up, so there is no rounding from printed tables.

How do I write a p value in LaTeX?

Use math mode with an italic p, as in $p = .032$ or $p < .001$; the p value calculator writes this line for you to copy.

Is anything I enter stored?

No. The calculator runs entirely in your browser, and nothing you type is sent or saved.