confidence intervals the percentile method.htm
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<H4><A name=SECTION00315130000000000000>Confidence Intervals : The percentile
method</A> </H4>As before we denote by <!-- MATH $G_n^*(t)=P_{F_n}\left(\widehat{\theta}^* \leq t \right)$ --><IMG
height=23 alt="$G_n^*(t)=P_{F_n}\left( \widehat{\theta}^* \leq t \right)$"
src="Confidence Intervals The percentile method.files/img296.png" width=22
align=middle border=0> the bootstrap distribution of <!-- MATH $\widehat{\theta}^*$ --><IMG height=32 alt=$\widehat{\theta}^*$
src="Confidence Intervals The percentile method.files/img297.png" width=368
align=bottom border=0>, approximated by <BR>
<P></P>
<DIV align=center><!-- MATH \begin{displaymath}\widehat{G}_n^*(t)=\#\{\widehat{\theta}^*\leq t\}/B\end{displaymath} --><IMG
height=45
alt="\begin{displaymath} \widehat{G}_n^*(t)= \char93 \{\widehat{\theta}^* \leq t \}/B\end{displaymath}"
src="Confidence Intervals The percentile method.files/img298.png" width=226
border=0> </DIV><BR clear=all>
<P></P>
<P>The percentile method consists in taking the <IMG height=40 alt=$1-2\alpha$
src="Confidence Intervals The percentile method.files/img316.png" width=372
align=middle border=0> confidence interval for <IMG height=17 alt=$\theta$
src="Confidence Intervals The percentile method.files/img19.png" width=14
align=bottom border=0> as being <BR>
<P></P>
<DIV align=center><!-- MATH \begin{displaymath}\left[\widehat{G}_n^{*-1}(\alpha),\widehat{G}_n^{*-1}(1-\alpha)\right]\end{displaymath} --><IMG
height=46
alt="\begin{displaymath}\left[ \widehat{G}_n^{*-1}(\alpha), \widehat{G}_n^{*-1}(1-\alpha) \right]\end{displaymath}"
src="Confidence Intervals The percentile method.files/img317.png" width=169
border=0> </DIV><BR clear=all>
<P></P>Theoretically speaking this is equivalent to replacement of the unknown
distribution <!-- MATH $G(x,F)=P_F(\widehat{\theta}<x)$ --><IMG height=37
alt="$G(x,F)=P_F(\widehat{\theta}<x)$"
src="Confidence Intervals The percentile method.files/img318.png" width=74
align=middle border=0> by the estimate <IMG height=45 alt=$G(x,F_n)$
src="Confidence Intervals The percentile method.files/img319.png" width=236
align=middle border=0>. <BR><I><!-- MATH $\fbox{The Percentile Algorithm }$ --><IMG height=18
alt="\fbox{The Percentile Algorithm }"
src="Confidence Intervals The percentile method.files/img320.png" width=46
align=middle border=0> : <BR></I>
<P>
<OL>
<LI>Input the level <IMG height=34 alt=$=2\alpha$
src="Confidence Intervals The percentile method.files/img321.png" width=25
align=bottom border=0> of the confidence interval
<LI>For b=1 to B do /* B is the number of bootstrap samples*/
<LI>For i=1 to n do /* Generation of Sample <IMG height=46 alt="${\cal X}_b$"
src="Confidence Intervals The percentile method.files/img322.png" width=91
align=middle border=0> */
<OL>
<LI>OBS=RANINT(1,n)
<LI>Add observation number OBS to the Sample <IMG height=46
alt="${\cal X}_b$"
src="Confidence Intervals The percentile method.files/img322.png" width=91
align=middle border=0> </LI></OL>
<LI>Compute <!-- MATH $\widehat{\theta}^*_b=\theta({\cal X}_b)$ --><IMG
height=37 alt="$\widehat{\theta}^*_b=\theta({\cal X}_b)$"
src="Confidence Intervals The percentile method.files/img323.png" width=64
align=middle border=0>
<LI>Combine the <!-- MATH $\widehat{\theta}^*_b=\theta({\cal X}_b)$ --><IMG
height=37 alt="$\widehat{\theta}^*_b=\theta({\cal X}_b)$"
src="Confidence Intervals The percentile method.files/img323.png" width=64
align=middle border=0> into a new data set THETA
<LI>Compute the <IMG height=18 alt=$\alpha$
src="Confidence Intervals The percentile method.files/img33.png" width=17
align=bottom border=0> and <IMG height=34 alt=$(1-\alpha)$
src="Confidence Intervals The percentile method.files/img324.png" width=28
align=middle border=0>'th quantiles for THETA. </LI></OL><BR>
<HR>
<ADDRESS>Susan Holmes 2002-01-12 </ADDRESS></BODY></HTML>
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