P-Value
Calculate p-values for statistical hypothesis testing
How to use P-Value
- 1Enter your test statistic and degrees of freedom (or the effect size and sample size).
- 2Select the tail type: one-tailed or two-tailed.
- 3Read the p-value and whether the result is significant at your chosen alpha.
Understanding p-values
p = P(test statistic ≥ observed | H0 true)A p-value is the probability of seeing results at least as extreme as yours if the null hypothesis were true.
A small p-value (below your alpha, often 0.05) suggests the observed effect is unlikely under the null, so you reject H0.
Frequently asked questions
Does p < 0.05 prove my theory?
No, it only argues against the null; it is not the probability that your theory is true.
One-tailed vs two-tailed?
Two-tailed splits the alpha on both ends; use one-tailed only with a pre-stated direction.
What is alpha?
The significance threshold you set beforehand, commonly 0.05, controlling false-positive rate.