Solution
= Solution
Use the A-group observed-minus-expected convention for the <stratified log-rank statistic>. At the first failure both teeth are at risk, so A has one observed event and null expectation $1/2$, giving $+1/2$. At the later B failure, A is no longer at risk; the A contribution is zero. \b[This patient's contribution is $+1/2$], favoring B. The opposite group convention reverses the sign but gives the same test.