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Re: [ccp4bb] I/sigma in XDS output
 

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CCP4bb <-- 2007 <-- April 2007 <-- 19 April 2007
Previous message:
Subject: MSc in Structural Biology and Biophysics at Manchester, UK
From: Martyn Winn m {- dot -} d {- dot -} winn {- at -} DL {- dot -} AC {- dot -} UK
Date: 2007-04-19 		Next message:
Subject: Re: Protein expression in Minimal media (M9)
From: artem {- at -} XTALS {- dot -} ORG artem {- at -} XTALS {- dot -} ORG
Date: 2007-04-19


Subject: Re: I/sigma in XDS output
From: Kay Diederichs kay {- dot -} diederichs {- at -} UNI-KONSTANZ {- dot -} DE
Date: 2007-04-19
Michele Lunelli wrote:
> Dear all,
> I'm a bit confused from the output of the CORRECT step in XDS. In one of
> the first tables I can read the mean I/sigma for each resolution shell,
> but these values are much different from the I/sigma reported in the
> table at the end of the output files, titled "completeness and quality
> of data set" for the full data range with signal/noise > -3.0. For
> example, from the first table I have I/sigma = 2 at 3.6 A, while from
> the second table I have I/sigma = 2 at 2.8 A!
> What is exactly the difference between the two values? And which one is
> reliable to decide the resolution cutoff?
>
>
> Thank you in advance,
>
> Michele Lunelli
> MPI for Infection Biology
> Berlin - Germany
>

Michele,

the first table, which is long and fine-grained in resolution, has (citing
CORRECT.LP):

I/Sigma = mean intensity/Sigma of a reflection in shell

and is thus talking about individual reflections _before_ merging symmetry
equivalents.


Later tables have (again citing CORRECT.LP):

I/SIGMA = mean of intensity/Sigma(I) of unique reflections
(after merging symmetry-related observations)

and are thus giving statistics _after_ merging.

The latter tables are suitable for deciding about the resol cutoff.

HTH,

Kay
--
Kay Diederichs http://strucbio.biologie.uni-konstanz.de
email: Kay.Diederichs@uni-konstanz.de Tel +49 7531 88 4049 Fax 3183
Fachbereich Biologie, Universität Konstanz, Box M647, D-78457 Konstanz

CCP4bb navigation

CCP4bb <-- 2007 <-- April 2007 <-- 19 April 2007
Previous message:
Subject: MSc in Structural Biology and Biophysics at Manchester, UK
From: Martyn Winn m {- dot -} d {- dot -} winn {- at -} DL {- dot -} AC {- dot -} UK
Date: 2007-04-19 		Next message:
Subject: Re: Protein expression in Minimal media (M9)
From: artem {- at -} XTALS {- dot -} ORG artem {- at -} XTALS {- dot -} ORG
Date: 2007-04-19


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