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O'Brien-Fleming type alpha spending: Boundary scales with t instead of sqrt(t) · case 02

Early looks spend far too little alpha and late looks too much.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Cumulative alpha spent at information fraction t is 2 - 2 Phi(z_{1-alpha/2} / sqrt(t)) (t capped at 1). Information fractions must strictly increase from 0, otherwise return None. Return the incremental alpha spent at each look rounded to 6.

Why this case matters

Spending functions let teams peek at experiments without inflating the false positive rate.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
two looks at stricter alpha	`[0.0, 0.01]`	`[0.00027, 0.00973]`	Failed

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