Past exam of the mathematics course of the University of Cambridge 2004 iii Paper 38 4 d Solution Created 2026-10-03 Updated 2026-10-14
There is a time-window discrepancy in the printed request: the probabilities supplied concern 26 weeks after sentence, whereas this part asks about 26 weeks after release. The prison data specify only the first 14 post-release weeks. The literal release-based comparison is not numerically identified without further follow-up risks and a common time origin for both arms.
For the intended common 26-week sentence-based endpoint, plan specifically for a 12% relative reduction from . Then , and . At 50% statistical power, , so the rare-event collaboration size at half power isEach system contributes 10,000 participants per arm. ThereforeAt , this is five systems for a two-sided test, or four systems for a prespecified one-sided test. For the two-sided calculation the required size is approximately 49,681 per arm, giving a 100,000-participant collaborative design after rounding to whole systems.
The 12% planning reduction is not the reduction implied by part (c): versus gives 10.2%. If one instead powers that calculated effect, the corresponding formula is , giving seven systems at two-sided 5%. Rounding the first mortality estimate to changes the latter answer to eight systems, so it should not be silently substituted into the 12% calculation. All these counts assume independent individual outcomes and the common sentence-based window; the time-origin alignment of clinical endpoints is essential.