Question

Consider a Gaussian linear model Y=aX+\epsilon in a Bayesian view. Consider the prior \pi (a)=1 for all a\in \mathbb {R}. Determine whether each of the following statements is true or false.

\pi (a) a uniform prior.



True

False

\pi (a) is a Jeffreys prior when we consider the likelihood L(Y=y|A=a, X=x) (where we assume x is known).



True

False

Consider a linear regression model \mathbf{Y}=\mathbb {X}{\boldsymbol \beta }+\sigma {\boldsymbol \varepsilon } where

{\boldsymbol \varepsilon }\in \mathbb {R}^ n is a random vector with \mathbb {E}[{\boldsymbol \varepsilon }]=\mathbf{0}, \mathbb {E}[{\boldsymbol \varepsilon }{\boldsymbol \varepsilon }^ T]=I_ n, and no further assumptions are made about {\boldsymbol \varepsilon }

\mathbb {X} is an n by p deterministic matrix, and \mathbb {X}^ T\mathbb {X} is invertible.

\sigma >0 is an unknown constant.

Let \hat{{\boldsymbol \beta }} denote the least squares estimator of \beta in this context. Determine whether each of the the following statements is true or false.

\hat{{\boldsymbol \beta }} is the maximum likelihood estimator for {\boldsymbol \beta }.



True

False

With the model written as \, \mathbf{Y}=\mathbb {X}{\boldsymbol \beta }+\sigma {\boldsymbol \varepsilon },\, \hat{{\boldsymbol \beta }} has dimension 1 \times p (i.e. is a row vector of length p).



True

False

\hat{\beta } has a Gaussian distribution (even for small n).



True

False

Under the same setup and assumptions, \mathbb {X}\hat{{\boldsymbol \beta }} is...
(Check all that apply.)



Equal to (\mathbb {X}^ T\mathbb {X})^{-1}\mathbb {X}^{T}\mathbf{Y}

An unbiased estimator of \mathbb {X}{\boldsymbol \beta }

A vector in \mathbb {R}^ p

Answer 1

False (it is a column vector)