Let \( X \) be a single (i.e. \( n=1 \) ) Gaussian random variable with unknown mean \( \mu \) and variance 1 . Consider the following hypotheses:
\[
H_{0}: \mu=0 \quad \text { vs } \quad H_{1}: \mu \neq 0 .
\]
(a)
1 point possible (graded)
Define a test \( \psi_{\alpha}: \mathbb{R} \rightarrow\{0,1\} \) with level \( \alpha \) that is of the form
\[
\psi_{\alpha}=\mathbf{1}\left\{f_{\alpha}(X)>0\right\},
\]
for some function \( f_{\alpha}: \mathbb{R} \rightarrow \mathbb{R} \).
We want our test \( \psi \) above to satisfy the following:
- Symmetric in the value of \( X \) about 0 , so \( f(X)=f(-X) \);
- Its "acceptance region" is an interval. (The acceptance region of a test is the region in which the null hypothesis is not rejected, i.e. the complement of its rejection region.)
Specify the function \( f_{\alpha}(X) \) in terms of \( \alpha \) below.