Article View: sci.math.stat
Article #395Re: Fwd: Standard Deviation.
From: mokaba
Date: Mon, 17 Aug 1992 21:57
Date: Mon, 17 Aug 1992 21:57
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In article <1992Aug14.231916.23479@magnus.acs.ohio-state.edu>, regeorge@magnus.acs.ohio-state.edu (Robert E George) writes: > > .>> (LOTS OF INTERESTING STAFF DELETED TO PRESERVE SPACE) >I'm not certain what "underestimate" means here: if you are speaking of >bias (bias being the difference between the estimand and the expected >value of the estimator), then > > --- _ _ > \ | X - Xbar |2 >T = / |_ _| > --- > ------------------ > n > >will "underestimate" the population variance *for any sample size n*. >T will always have a negative bias *regardless of how large a sample is >used to compute T*. > >More intuitively, if we take a very sample, we are less likely to get >extreme values and so our notion of what the population variance is (note >that I am not proposing some particular estimator) will be unrealistic. >For instance, I give an exam to two students. Their scores are 67 and >71. I think, "Gee, there's not a lot of variability in these scores." >But then 8 more students take the exam: > 60 78 100 38 50 88 99 39 > >and it now is clear there *is* more variability in these scores. > >But let me reiterate that T will *always* have a negative bias for the >population variance whatever the sample size is MY IGNORAMUS QUESTION? Does't that negative bias decrease as the sample size approaches population size? thanks in anticipation for answering my question. Mokaba
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Newsgroups: sci.math.stat Path: arc1-ca.pugleaf.net!sparky!uunet!centerline!noc.near.net!news.cs.brandeis.edu!binah.cc.brandeis.edu!MOKABA From: mokaba@binah.cc.brandeis.edu Subject: Re: Fwd: Standard Deviation. Message-ID: <1992Aug17.215753.6932@news.cs.brandeis.edu> Sender: news@news.cs.brandeis.edu (USENET News System) Reply-To: mokaba@binah.cc.brandeis.edu Organization: Brandeis University References: <1992Aug14.172833.11844@cbfsb.cb.att.com> <seX2yRq00Uh785H2EB@andre,<1992Aug14.231916.23479@magnus.acs.ohio-state.edu> Date: Mon, 17 Aug 1992 21:57:53 GMT Lines: 38