The t-statistic is a widely-used scale-invariant statistic for testing the null hypothesis that the mean is zero. Martingale methods enable sequential testing with the t-statistic at every sample size, while controlling the probability of falsely rejecting the null. For one-sided sequential tests, which reject when the t-statistic is too positive, a natural question is whether they also control false rejection when the true mean is negative. We prove that this is the case using monotone likelihood ratios and sufficient statistics. We develop applications to the scale-invariant t-test, the location-invariant χ 2 -test and sequential linear regression with nuisance covariates.

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doi.org/10.1016/j.spl.2025.110574
Statistics and Probability Letters
Flexible Statistical Inference
Centrum Wiskunde & Informatica, Amsterdam (CWI), The Netherlands

Grünwald, P., & Koolen-Wijkstra, W. (2026). Supermartingales for one-sided tests: Sufficient monotone likelihood ratios are sufficient. Statistics and Probability Letters, 229, 110574:1–110574:5. doi:10.1016/j.spl.2025.110574