# P Value Calculator

An interactive p-value calculator with solutions and graphs for Z-scores, T-scores, F-scores, and Chi-square scores.

### P value calculator

The p-value calculator calculates the p-value for Z score, T score, F score and Chi-square score.

If you don't have the score you may use one of the following calculators that will compute the score and the p-value:

One sample Z-test, Two sample Z-test, One sample T-test,Two-Sample T (Welch's),Two-Sample T-test (equal), Chi-squared test, F-test and more.

### How to use the p-value calculator

- Select the relevant distribution: Normal distribution, T distribution, Chi-square distribution, or F distribution
- Choose the relevant tail; the default is two tails.
- Enter the significance level (α); the default is 0.05.
- Input the score which is the statistic value.
- Provide the distribution's parameters.
- Press the 'calculate' button to get the p-value, chart, and solution.

### What is p value?

**The p-value is the probability of obtaining the current statistical result under the assumption that H _{0} is correct.**

If you decide to reject the H

_{0}, the p-value represents the probability of making a mistake, specifically a type I error — rejecting a correct H

_{0}. A commonly used rule defines a significance level of 0.05. When the p-value is smaller than the significance level, you can reject the null hypothesis with a low chance of error. Another commonly used significance level is 0.01.

### When is p value significant?

The p-value is significant when it is equal to or lower than the significance level (α). This indicates that the probability of the null hypothesis being correct and obtaining such a score is very low, lower than the significance level.

### Why do we reject the null hypothesis when the p-value is small?

The p-value represents the probability of rejecting a correct H_{0}. When the p-value is **small**, the probability of rejecting a correct H_{0} is **small**, hence the probability of making a mistake is **small**.

### P value formula

X is the test statistic value, and you know the distribution of X.

For example X may be Z, T etc.

- Left tailed: P-value = p(x≤X)
- Right tailed: P-value = 1 - p(x≤X)
- Two tailed: P-value = 2 * Min( p(x≤X), 1 - p(x≤X) )