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SigmaCalc
Convert a test statistic into the probability of seeing a result this extreme by chance alone.
A one-tailed test only asks whether a result is significantly higher (or lower) than expected in one direction. A two-tailed test asks whether it's significantly different in either direction — and roughly doubles the p-value for the same z-score.
The 0.05 threshold is a widely used convention, not a law of nature — a p-value just below 0.05 and one just above it aren't meaningfully different in strength of evidence. Treat it as one input into a decision, not a strict pass/fail line.
p-value
0.05
Significant at α = 0.05
What you entered
Area beyond |z| under the normal curve
1 − Φ(1.96)= 0.025Double it for a two-tailed test
2 × 0.025= 0.05Result
p-value: 0.05
A two-tailed test at z = 1.96 gives a p-value of 0.05 — below 0.05, so the result is statistically significant at the conventional threshold.