= Solution
Under a country-specific <constant hazard survival model>, let $D_k$ be the number of deaths and $Y_k$ the total <person-time at risk> in country $k$. The likelihood is proportional to
$$
L_k(\lambda_k)\propto\lambda_k^{D_k}e^{-\lambda_kY_k},
$$
so the <maximum-likelihood estimator> is $\widehat\lambda_k=D_k/Y_k$. Test $H_0:\lambda_0=\lambda_1$ by a <likelihood-ratio test>, <score test>, or <Wald test>; equivalently, give $D_k$ a <Poisson distribution> with mean $\lambda_kY_k$ and test the country coefficient in a <Poisson regression> with offset $\log Y_k$.
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