 Solution

In the final data, the only deaths by treatment duration twelve are B and E. ThusThe month-24 estimate already has this numerical value, so month 24 is the first twelve-monthly analysis satisfying ${\hat{F}}_M(12)={\hat{F}}_{\infty }(12)$.

Equality is not yet knowable at month 24 because patient F has only nine months of follow-up and could still die before duration twelve. Patient F reaches twelve complete months at the end of month 27, so month 36 is the earliest scheduled analysis at which the final value at duration twelve is evaluable.