@@ -18,31 +18,36 @@ the presence of missing observations. Consider the model defined as:
1818Missingness is modeled by a binary process \( \mathbf{Z} \in \{ 0,1\} ^n\) with
1919\( Z_i = 1\) indicating an observation and \( Z_i = 0\) a missing observation. The missingness process is independent of
2020$\mathbf{Y}$ and follows the definition:
21+
2122\begin{equation}
2223 Z_i =
2324\begin{cases}
2425 Z_ {i-1}, & \text{with probability } \rho, \\
2526 W_i \sim \mathrm{Bernoulli}(\mu(\bm{\vartheta})), & \text{with probability } 1-\rho,
2627\end{cases}
2728\end{equation}
29+
2830with expectation $\mu(\boldsymbol{\vartheta}) = \mathbb{E}[ Z_i] \in (0, 1] $ for
2931all $i \in \{ 1, \ldots, n\} $, with covariance matrix
3032$\boldsymbol{\Lambda}(\boldsymbol{\vartheta}) = \operatorname{var}\left(\mathbf{Z}\right)
3133\in \mathbb{R}^{n\times n}$ whose structure is assumed known up to the
3234parameter vector $\boldsymbol{\vartheta} \in \boldsymbol{\Upsilon} \subset \mathbb{R}^k$.
3335The observed series is
36+
3437\[
3538 \tilde{\mathbf{Y}} = \mathbf{Y} \odot \mathbf{Z}.
3639\]
3740
3841The design matrix with rows zeroed out for missing observations
3942can be written as \( \tilde{\mathbf{X}} = \left(\mathbf{Z} \otimes \mathbf{1}^T\right) \odot \mathbf{X}\) .
4043The least‑squares estimator based on observed data is
44+
4145\[
4246 \hat{\boldsymbol{\beta}} =
4347 \left(\tilde{\mathbf{X}}^T \tilde{\mathbf{X}}\right)^{-1}\tilde{\mathbf{X}}^T \tilde{\mathbf{Y}},
4448\]
4549and we compute residuals
50+
4651\( \hat{\boldsymbol{\varepsilon}} = \tilde{\mathbf{Y}} - \tilde{\mathbf{X}}\hat{\boldsymbol{\beta}}\) .
4752
4853We then estimate the parameters of the missingness process via maximum
@@ -66,7 +71,7 @@ $\hat{\boldsymbol{\beta}}$ is then obtained as:
6671\begin{equation}
6772\mu(\hat{\boldsymbol{\vartheta}})^{-2}(\mathbf{X}^{T}\mathbf{X})^{-1}
6873\mathbf{X}^{T} \boldsymbol{\Sigma}(\hat{\boldsymbol{\gamma}}, \hat{\boldsymbol{\vartheta}})
69- \mathbf{X} (\mathbf{X}^{T}\mathbf{X})^{-1}
74+ \mathbf{X} (\mathbf{X}^{T}\mathbf{X})^{-1}.
7075\end{equation}
7176
7277
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