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So much discussions. We shall expect much better definitions and examples which can offer clarity. Regards, Shao On Sat, Mar 23, 2019 at 9:09 PM Martin Holt < [log in to unmask]> wrote: > This and the other postings under this thread would be better placed under > the Google Group MedStats (I am biased...I founded MedStats). > One advantage over AllStat is that all discussions are visible even if you > aren't yet a member. To post you do need to join. > MedStats boasts over 1560 members, including a number of the most notable > Medical Statisticians..... > Martin Bland and his late partner Douglas G. Altman...........MedStats > wins over other mailing lists in that all previous posts are > searchable...as an archive.....Frank Harrell JnrStephen SennAbhaya Indrayan > (my co-author...see below)John Whittington (with MedStats since its > conception)Scott R Millis (aka "Professor Mean") > Marc SchwartzRobert NewcombeMalcolm CampbellBendix Carstensen, member of > the "R Core Team" (developing R programs) > I hope that this helps... > Faithfully yours > Martin P. Holt > Freelance Medical Statistician > If you can't explain it simply, you don't understand it well > enough.....Einstein > > > Concise > > Encyclopedia > > of Biostatistics for > > MedicalProfessionals > > > > Abhaya IndrayanMartinP. Holt > > > https://www.crcpress.com/Concise-Encyclopedia-of-Biostatistics-for-Medical-Professionals/Indrayan-Holt/9781482243871 > > Linked In: > https://www.linkedin.com/in/martin-holt-3b800b48?trk=nav_responsive_tab_profile > > ----- Forwarded message ----- From: M. A. Mansournia < > [log in to unmask]>To: "[log in to unmask]" > <[log in to unmask]>Sent: Friday, 22 March 2019, 11:20:13 GMTSubject: > Re: Precision & accuracy > With i.i.d. sampling, uncorrelatedness of the sample mean and sample > variance holds for any symmetric distribution with finite second moment. > The stronger assumption of independence of mean and variance only holds for > Normal distribution by Geary’s theorem. > > > > > Best, > > Mohammad > > > Sent from Yahoo Mail for iPhone > > > On Friday, March 22, 2019, 2:10 PM, Cole, Tim <[log in to unmask]> wrote: > > Thanks Andy. Yes you are right - I should have specified the normal > distribution. > > Best wishes, > Tim > > > [log in to unmask] <mailto:[log in to unmask]> Phone +44(0)20 7905 > 2666 Fax +44(0)20 7905 2381 > Population, Policy and Practice Programme > UCL Great Ormond Street Institute of Child Health, London WC1N 1EH, UK > > > > > On 22/03/2019, 09:22, "Andrew Salmon" <[log in to unmask]> wrote: > > >Hi Tim > >that feels right, but are the mean and variance uncorrelated? in > >mathematical analysis the mean always seems to be related to the first > >derivative of something or other, and the variance to the second. Not > >only that, but in most parametric distributions, the mean and variance > >incorporate the same parameter, with the normal distribution being the > >exception? > > > >Or do I just need more coffee this morning...? > > > >Andy > > > >On Fri, 22 Mar 2019 at 09:04, Cole, Tim <[log in to unmask]> wrote: > >> > >> Sorry to come late to the party. > >> > >> It¹s worth stating that accuracy relates to the mean of a sample of > >>values > >> (in that bias is the difference between the sample mean and the true > >> mean), whereas precision relates to the sample variance (or its > >>inverse). > >> Hence the two are uncorrelated by definition. > >> > >> Best wishes, > >> Tim Cole > >> > >> [log in to unmask] <mailto:[log in to unmask]> Phone +44(0)20 7905 > >> 2666 Fax +44(0)20 7905 2381 > >> Population, Policy and Practice Programme > >> UCL Great Ormond Street Institute of Child Health, London WC1N 1EH, UK > >> > >> ------------------------------ > >> > >> > >> > >> >Date: Thu, 21 Mar 2019 09:56:44 +0000 > >> >From: Allan Reese <[log in to unmask]> > >> >Subject: Precision & accuracy (MY conclusion) > >> > > >> >Thanks to all for comments. Martin Bland suggests, "The standard > >> >statistical usage, as I understand it, is that precision refers to how > >> >close repeated observations are to one another, and accuracy how far > >> >they are from the true value." That, and similar comments, correspond > >>to > >> >the definitions in Kendall & Buckland (Dictionary of Statistical Terms, > >> >4th ed), though I would use "reliability" for the former. As K&D > >> >comment, the "precision" of an estimator varies with the square root of > >> >the number of observations, but it's not quite the sense here. > >> > > >> >John Whittington sent me a great hint off-list, "Modern technology is > >> >such that it is only too easy to produce such a device which displays > >> >umptreen more DPs than is sensible in relation to the accuracy of the > >> >measurement." That's what happen here. The device (digital calliper) > >>has > >> >a standard LED display that shows 2dp, but it was flimsily constructed > >> >and flexed when applied to an object. There is no reason to believe the > >> >measurements are biased, especially as the "accuracy" is quoted as +/-. > >> >To my mind, it means a reading of, say 3.45 could mean anything from > >> >3.25 to 3.65, so I have doubts even rounding to 0dp! > >> > > >> >Fortunately, the model I use is made of metal, has a quoted precision > >>of > >> >0.02 (and a 2dp display), so I'm happy rounding to 1dp. > >> > > >> >There is clearly much imprecision, and confusion, in the use of the > >>word > >> >"precision" with regard to measurement (recording), calculation > >> >(numerical analysis), and general use in the language - Collins > >> >Dictionary was no help at all! > >> > > >> >Allan > >> > > >> > >> You may leave the list at any time by sending the command > >> > >> SIGNOFF allstat > >> > >> to [log in to unmask], leaving the subject line blank. > > > You may leave the list at any time by sending the command > > SIGNOFF allstat > > to [log in to unmask], leaving the subject line blank. > > > > > > You may leave the list at any time by sending the command > > SIGNOFF allstat > > to [log in to unmask], leaving the subject line blank. > > You may leave the list at any time by sending the command > > SIGNOFF allstat > > to [log in to unmask], leaving the subject line blank. > You may leave the list at any time by sending the command SIGNOFF allstat to [log in to unmask], leaving the subject line blank.