Past exam of the mathematics course of the University of Cambridge / 2026 / iii / Paper 207 / 5 / b / i / Solution

Use each matched pair as a separate stratum with its own baseline hazard and fit one common treatment coefficient $\beta$. The Stratified Cox model partial likelihood multiplies the within-pair risk-set contributions, eliminating all pair-specific baselines. Test $H_0:\beta =0$ by the corresponding conditional score, likelihood-ratio, or Wald test.

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