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Complier average causal effect: Control crossover is ignored in compliance · case 05

CACE is understated when control users can reach the feature through another path.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Outcome sums cover every assigned user. ITT = outcome_sum_t / assigned_t - outcome_sum_c / assigned_c. Compliance difference = took_t / assigned_t - took_c / assigned_c (control users can cross over). CACE = ITT / compliance difference when that difference is positive, else None. Nonpositive assignment counts -> None. Return [ITT, compliance difference, CACE] rounded to 6.

Why this case matters

Opt-in features have partial uptake; the effect on adopters needs an instrumental-variable estimate.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
crossover in control reduces compliance difference	`[0.6, 0.6, 1.0]`	`[0.6, 0.5, 1.2]`	Failed

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