School-based human papillomavirus (HPV) vaccination programmes depend on consent forms that are frequently incomplete, and the resulting catch-up scheduling decisions are made under uncertainty about which girls remain unvaccinated. Because no observational cohort is available, the study characterises the operating characteristics of the before-after-control-impact (BACI) estimator that would underlie such an emulation, using a declared variance structure with between-cluster standard deviation 6.0, residual standard deviation 4.5 and intraclass correlation 0.64. Power was estimated across 2000 replications per design cell for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. The analysis identifies the cluster count required for 80% power at a 5 percentage point effect and maps the minimum detectable effect across the design grid. The contribution is a design-theoretic account of when a target trial emulation of catch-up scheduling can distinguish equitable from inequitable coverage, together with the formal conditions under which consent form incompleteness biases the emulation rather than merely adding noise.
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Bouzid et al. (2026) studied this question.
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