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From |
"Roys, Nicolas A." <Nicolas_A_Roys@brown.edu> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: boostrap with stata |

Date |
Thu, 18 Aug 2005 14:04:17 -0400 |

You wrote : ----------------------------------------------------------------------------------------- From: owner-statalist@hsphsun2.harvard.edu on behalf of Timothy.Mak@iop.kcl.ac.uk Sent: Thu 8/18/2005 8:39 AM To: statalist@hsphsun2.harvard.edu Subject: Re: st: boostrap with stata (elementary question) Hi, To me, It seems what Nicholas Roys wanted was: Var(estSD(ice)/estSD(ich)) whereas Clive gave the procedure to give: Var(ice/ich) I think to calculate the former result, you need to write your own program. Tim ----------------------------------------------------------------- Tim is right I want Var(estSD(ice)/estSD(ich)) "writing my own program" is probably the solution. I try to use this one : program ratio, rclass version 8.0 summarize ice local ice = r(sd) summarize ich local ich = r(sd) return ratio = `ice'/`ich' end Then, I write : bootstrap "ratio" r(ratio), reps(1000) but It doesn't work, stata saying : command -> ratio error when command executed on original dataset under version 8 control r(198); if anybody has a suggestion... nicolas "Clive Nicholas" <Clive.Nicholas@newcastle.ac.uk> Sent by: owner-statalist@hsphsun2.harvard.edu 18/08/2005 12:33 Please respond to statalist@hsphsun2.harvard.edu To statalist@hsphsun2.harvard.edu cc Subject Re: st: boostrap with stata (elementary question) Nicolas A. Roys wrote: > I want to bootstrap the variance of the standard deviation of "ice" and > the standard deviation of "ich" > so I think the stata command is simply : > bs "summarize ice, detail" "r(sd)", rep(1000) > bs "summarize ich, detail" "r(sd)", rep(1000) > but how can I can bootstrap the variance of the ratio > standard deviation of "ice" divided by standard deviation of "ich" ? Perhaps I'm missing something obvious, but I don't see the need for any further -bootstrap-ping. All I think you need do is the following: (1) -generate- a new variable for the ratio of ("ice"/"ich"); (2) *then* -summarize- that variable: since it gives the standard deviation, all you need do is square it to get the variance of that ratio. By the way, as Nick Cox has counselled to the list on various occasions, it's not a bright idea to say that you're asking an 'elementary' question to Statalist. Such posts often get deleted on sight, because it suggests that the answer is also elementary, indeed so elementary that you didn't really need to ask the list in the first place! Hope that helps. CLIVE NICHOLAS |t: 0(044)7903 397793 Politics |e: clive.nicholas@ncl.ac.uk Newcastle University |http://www.ncl.ac.uk/geps <http://www.ncl.ac.uk/geps> Whereever you go and whatever you do, just remember this. No matter how many like you, admire you, love you or adore you, the number of people turning up to your funeral will be largely determined by local weather conditions. * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html <http://www.stata.com/support/faqs/res/findit.html> * http://www.stata.com/support/statalist/faq <http://www.stata.com/support/statalist/faq> * http://www.ats.ucla.edu/stat/stata/ <http://www.ats.ucla.edu/stat/stata/> * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html <http://www.stata.com/support/faqs/res/findit.html> * http://www.stata.com/support/statalist/faq <http://www.stata.com/support/statalist/faq> * http://www.ats.ucla.edu/stat/stata/ <http://www.ats.ucla.edu/stat/stata/>

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**Follow-Ups**:**RE: st: boostrap with stata***From:*"Scott Merryman" <smerryman@kc.rr.com>

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