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:
>
> <I> 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]
>>> *******************************************
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