Past exam of the mathematics course of the University of Cambridge / 2025 / iii / Paper 207 / 4 / a / ii / Solution

No. The high-dose expectation isAlthough both groups start with five patients, censoring removes two low-dose patients at month 3 and one high-dose patient at month 1. Their later risk sets therefore differ; only the sum $E_A+E_B=5$ must equal the total observed failures.