H. Jeffreys (1961) in his work Theory of Probability published by Oxford Univ. Press, suggested
a rule to generate a prior distribution of a parameter $\theta$ associated with the sampling
distribution $p(y | \theta)$. The Jeffreys prior distribution is of the form:
Where:
$P_J(\theta) \propto \sqrt{I(\theta)},$
$I(\theta) = -E_{y|\theta} \left( \frac{d^2}{d\theta^2} log p(y | \theta) \right)$
is the expected Fisher information.
As defined above, you are asked to determine the following,
a) Consider a single observation from the sampling distribution,
$x_i | \theta, \theta^2 \stackrel{iid}{\sim} N(\theta, \theta^2)$, donde $\theta > 0$.
As defined at the beginning, determine Jeffrey's prior, and represent the distribution
graphically and analyze.
b) The Jeffreys prior for the beta binomial model is known to be,
$p(\theta) \propto \theta^{-1/2}(1-\theta)^{-1/2}$
Reparameterize the Binomial distribution with $\phi = logit(\theta),$ and obtain the
Jeffreys prior distribution for this sampling distribution.
To check the above result, apply the change of variables formula
to obtain the prior density of $\phi$. Does the invariance of the Jeffreys prior hold
under reparameterizations?