{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "# Duality between confidence sets and hypothesis tests\n", "\n", "### We will observe $X \\sim \\mathbb P_\\mu$, where $\\mu \\in \\Theta$. \n", "+ $\\Theta$ is known\n", "+ $\\theta \\rightarrow \\mathbb P_\\theta$ is known\n", "+ $\\mu$ is unknown\n", "+ $X$ takes values in $\\mathcal X$.\n", "\n", "(We will ignore issues of measurability here: tacitly assume that for all $\\theta \\in \\Theta$, $A_\\eta$ is $\\mathbb P_\\theta$-measurable\n", "and that $\\mathcal I(X)$ is set-valued $\\mathbb P_\\theta$-measurable function.)\n", "\n", "
Definition
\n", " \n", "$A_\\theta \\subset \\mathcal X$ is the acceptance region for a level-$\\alpha$ test of the hypothesis $\\mu = \\theta$ iff\n", "\\begin{equation*} \\mathbb P_\\theta (X \\notin A_\\theta) \\le \\alpha.\\end{equation*}\n", " \n", "Definition
\n", " \n", "$\\mathcal I(X)$ is a $1-\\alpha$ confidence set for $\\mu$ iff \n", "\\begin{equation*} \\forall \\theta \\in \\Theta, \\;\\;\\; \\mathbb P_\\theta ( \\mathcal I(X) \\ni \\theta) \\ge 1-\\alpha.\\end{equation*}\n", "\n", "Proposition
\n", "\n", "Suppose \n", "\\begin{equation*} \\{A_\\theta: \\theta \\in \\Theta \\}\\end{equation*}\n", "is a family of level-$\\alpha$ acceptance regions. Then \n", "\\begin{equation*} \\mathcal I(X) := \\{ \\theta \\in \\Theta: X \\in A_\\theta \\}\\end{equation*}\n", "is a $1-\\alpha$ confidence set for $\\mu$.\n", " \n", "Proof
\n", "\n", "For any $\\theta \\in \\Theta$,\n", "\\begin{equation*} \\mathbb P_\\theta \\left (\\{ \\eta \\in \\Theta: X \\in A_\\eta \\} \\ni \\theta \\right ) = \n", " \\mathbb P_\\theta ( X \\in A_\\theta ) \\end{equation*}\n", "\\begin{equation*} \\ge 1-\\alpha.\\end{equation*}\n", " \n", "