How it's calculated
p = 2 × [1 − F(|stat|)] (two-tailed)
stat = test statistic, F = cumulative distribution of the standard normal (z-test) or Student's t with df degrees of freedom. One-tailed: p = 1 − F(stat). Reject H₀ when p ≤ α.
Reference ranges
| P-value | Common reading |
|---|---|
| Below 0.01 | Strong evidence against the null |
| 0.01 to 0.05 | Significant at the usual 0.05 level |
| Above 0.05 | Not significant at 0.05 |
Common questions
What does the p-value mean?
It is the probability of seeing a result at least as extreme as yours if the null hypothesis were true. A small p-value suggests the null is unlikely.
Should I use one-tailed or two-tailed?
Use two-tailed when you only care that there is a difference in either direction, and one-tailed when you have a specific direction predicted in advance.