Sequential Testing Calculator

SPRT: Sequential Probability Ratio Test

Parameters

%
%
one-tail
20% = 80% power
How it works: SPRT tests hypotheses sequentially, allowing you to stop early when evidence is sufficient. Continue collecting data until you hit an upper boundary (reject null) or lower boundary (accept null).

Results

Upper Boundary (LR)
Stop & reject null (significant)
Lower Boundary (LR)
Stop & accept null (not significant)
Expected Sample Size
Expected observations per variant
Savings vs Fixed-Horizon
Reduction in required sample size

Likelihood Ratio Progression

The chart shows a typical SPRT path. The likelihood ratio starts at 1 and evolves with each observation. When it crosses the upper boundary, stop and declare a winner. When it crosses the lower boundary, stop and conclude no significant effect.

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