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CCP4BB  March 2010

CCP4BB March 2010

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Subject:

Re: Equation for combining measurements

From:

Jacob Keller <[log in to unmask]>

Reply-To:

Jacob Keller <[log in to unmask]>

Date:

Thu, 18 Mar 2010 12:40:05 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (72 lines)

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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