FA-74454 / Experiment statistics / Member archive

Group sequential stopping rule: A statistic equal to the boundary does not stop · case 04

The trial runs past a look whose statistic lands exactly on the boundary.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Looks beyond len(boundaries) are ignored. At look i: stop for efficacy if |z| >= boundaries[i]; else before the final planned look stop for futility if z < futility[i]; at the final planned look without efficacy return null. If data ends earlier return [continue, last look index or -1]. Return [decision, look index].

Why this case matters

Interim analyses control false positives only if the stopping rule is executed exactly.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
interim look sample 1	`["null", 2]`	`["efficacy", 0]`	Failed

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