Statistics
Statistics
p-Value Calculator
Compute p-values from t-, z-, and chi-square statistics, with significance interpretation in plain language.
Input
Test details
The t, z, or χ² value reported by your statistical software.
For an independent-samples t-test: df = n₁ + n₂ − 2.
Output
p-value
Two-tailed t-test
- p
- 0.0266
- p < .05, significant
LaTeX:
$p = 0.027$p-values are computed using standard analytic CDFs (Abramowitz & Stegun for normal, regularized incomplete beta for t and chi-square). Accurate to ~6 decimals for typical research ranges.
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One- vs two-tailed, and which you should use
A two-tailed test asks "is there a difference?" (either direction). A one-tailed test asks "is the value larger / smaller?" (specified direction). Two-tailed is the default in psychology, education, and most social sciences; one- tailed is justifiable only when your hypothesis truly is directional and pre-registered. The convention exists because one-tailed tests halve the p-value, making it easier to find "significance", which is why journals are suspicious of them when used post hoc.
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