Let \(\epsilon _{1}, \ldots , \epsilon _{n}\) and \(\eta _{1}, \ldots , \eta _{m}\) be independent normal random variables with \(\mathbb {E}\epsilon _{i} = \mathbb {E}\eta _{j} = 0\) and \(\mathbb {E}\epsilon _{i}^{2} = 1, \mathbb {E}\eta _{j}^{2} = 4\). We have the models
\[X_{i} = \beta _{1} + \beta _{2} x_{i} + \epsilon _{i}, 1 \le i \le n,\]
\[Y_{i} = \beta _{1} + \beta _{3} y_{i} + \eta _{i}, 1 \le i \le m,\]
where the \(x_{i}, y_{i}\) are given and non-random.
- Find the maximum likelihood estimator for \((\beta _{1}, \beta _{2}, \beta _{3} )\).
- Compute the distribution of the estimator.