CALTRX

P-value Calculator

Enter a z-score to compute p-values instantly.

p = 2*P(Z>=|z|) for two-tail
z= Test statistic
p= P-value

Tips & Notes

  • ✓Report exact p-values.
  • ✓Choose test direction before data.
  • ✓Large samples make tiny effects significant.
  • ✓Consider effect size too.

Common Mistakes

  • ✗Interpreting p as P(null true).
  • ✗Choosing tails after seeing data.
  • ✗Treating 0.049 differently from 0.051.
  • ✗Ignoring effect size.

P-value Calculator Overview

What This Calculator Does

Computes p-values from z-scores using the standard normal distribution. Provides one-tailed and two-tailed results with significance assessment.

P-value Interpretation

The p-value is the probability of data this extreme if the null hypothesis is true. It is NOT the probability the null is true. Small p-values (< 0.05) suggest evidence against the null.

One vs Two-tailed

One-tailed checks one direction. Two-tailed checks both. Most research uses two-tailed tests. Two-tailed p = 2 * one-tailed p.

Thresholds

Alpha=0.05 is conventional. Medicine often uses 0.01. Particle physics uses 5sigma. Choose threshold before seeing data.

Frequently Asked Questions

<5% chance of data this extreme if null is true.

z=1.96.

Only with pre-specified directional hypothesis.

The P-value Calculator uses standard validated formulas and provides results accurate to multiple decimal places. Review the step-by-step explanation to verify each calculation.