Re: [ccp4bb] Reasoning for Rmeas or Rpim as Cutoff

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

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From: Richard Gillilan reg8 {- at -} CORNELL {- dot -} EDU
Date: 2012-01-27

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Subject: Re: Reasoning for Rmeas or Rpim as Cutoff
From: Graeme Winter graeme {- dot -} winter {- at -} GMAIL {- dot -} COM
Date: 2012-01-28

Hi Jacob,

I think a lot of people do use I/sigma :o)

However sigma is in some cases poorly defined, and the merging
residuals you refer to are calculated only from the I values and are
related to I/sigma anyhow... Of course the R values are sometimes also
poorly defined for low multiplicity data.

Best wishes,

Graeme

On 27 January 2012 17:55, Jacob Keller wrote:
> Clarification: I did not mean I/sigma of 2 per se, I just meant
> I/sigma is more directly a measure of signal than R values.
>
> JPK
>
> On Fri, Jan 27, 2012 at 11:47 AM, Jacob Keller
> wrote:
>> Dear Crystallographers,
>>
>> I cannot think why any of the various flavors of Rmerge/meas/pim
>> should be used as a data cutoff and not simply I/sigma--can somebody
>> make a good argument or point me to a good reference? My thinking is
>> that signal:noise of >2 is definitely still signal, no matter what the
>> R values are. Am I wrong? I was thinking also possibly the R value
>> cutoff was a historical accident/expedient from when one tried to
>> limit the amount of data in the face of limited computational
>> power--true? So perhaps now, when the computers are so much more
>> powerful, we have the luxury of including more weak data?
>>
>> JPK
>>
>>
>> --
>> *******************************************
>> Jacob Pearson Keller
>> Northwestern University
>> Medical Scientist Training Program
>> email: j-keller2@northwestern.edu
>> *******************************************
>
>
>
> --
> *******************************************
> Jacob Pearson Keller
> Northwestern University
> Medical Scientist Training Program
> email: j-keller2@northwestern.edu
> *******************************************

CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: BioSAXS beamtime available
From: Richard Gillilan reg8 {- at -} CORNELL {- dot -} EDU
Date: 2012-01-27

Next message:
Subject: Re: MAD
From: Peter Moody pcem1bigfiles {- at -} GMAIL {- dot -} COM
Date: 2012-01-28