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Re: Equation for combining measurements

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Thu, 18 Mar 2010 17:45:11 +0000

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 ```It's based on an assumption of Gaussian errors, but it is certainly arguable about whether this is the best weighting scheme Phil On 18 Mar 2010, at 17:40, Jacob Keller wrote: > Okay, I think I understand: > > is the weighted average of the equivalent scaled intensities, with 1/sigma^2 as weight for each reflection. > > Is there a derivation/rationale for using 1/sigma^2 as the weight? I see that this would give more credence to better I/sigma measurements, but I do not yet understand why this is exactly the correct weight. Why not simply 1/sigma, or 1/sigma^87? > > I apologize for the basic nature of this inquiry, but I would like to understand all of this fully. And...you can always ignore! > > Jacob > > ******************************************* > Jacob Pearson Keller > Northwestern University > Medical Scientist Training Program > Dallos Laboratory > F. Searle 1-240 > 2240 Campus Drive > Evanston IL 60208 > lab: 847.491.2438 > cel: 773.608.9185 > email: [log in to unmask] > ******************************************* > > ----- Original Message ----- From: "Jim Pflugrath" <[log in to unmask]> > To: <[log in to unmask]> > Sent: Thursday, March 18, 2010 10:12 AM > Subject: Re: [ccp4bb] Equation for combining measurements > > >> The weighted mean is used. Wikipedia >> http://en.wikipedia.org/wiki/Weighted_mean has the equation(s). >> >> >> -----Original Message----- >> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of >> Eleanor Dodson >> Sent: Thursday, March 18, 2010 4:59 AM >> To: [log in to unmask] >> Subject: Re: [ccp4bb] Equation for combining measurements >> >> Isnt it in the scala documentation? >> Eleanor >> >> Jacob Keller wrote: >>> Dear Crystallographers, >>> >>> A basic question: what is the equation currently used to combine/merge >>> multiple measurements of I and sigI? (Or a reference would be fine as >>> well (or maybe better.)) >>> >>> Thanks, >>> >>> Jacob Keller >>> >>> ******************************************* >>> Jacob Pearson Keller >>> Northwestern University >>> Medical Scientist Training Program >>> Dallos Laboratory >>> F. Searle 1-240 >>> 2240 Campus Drive >>> Evanston IL 60208 >>> lab: 847.491.2438 >>> cel: 773.608.9185 >>> email: [log in to unmask] >>> ******************************************* ```