Re: [ccp4bb] definition of I Sigma I

[Richard Gillilan]

There was a detailed and useful discussion of this on this list back  
around Dec 1, 2003. If you search in the archives for I on sig I  
you will find it.


Best

Richard


On Dec 10, 2008, at 5:14 PM, ANDY DODDS wrote:


Hi,

does anyone have a definition of I Sigma I please.  Any definitions
that i have found are not very informative for novices.


thanks

andy

Re: [ccp4bb] definition of I Sigma I [SEC=UNCLASSIFIED]

[DUFF, Anthony]

My summary can be found at
http://wserv1.dl.ac.uk/list-archive-public/ccp4bb/2003-10/msg00431.html 

Anthony

Anthony DuffTelephone: 02 9717 3493  Mob: 043 189 1076

-Original Message-
From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of
Richard Gillilan
Sent: Friday, 12 December 2008 9:37 AM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] definition of I Sigma I

There was a detailed and useful discussion of this on this list back  
around Dec 1, 2003. If you search in the archives for I on sig I  
you will find it.

Best

Richard


On Dec 10, 2008, at 5:14 PM, ANDY DODDS wrote:

 Hi,

 does anyone have a definition of I Sigma I please.  Any definitions
 that i have found are not very informative for novices.


 thanks

 andy

[ccp4bb] definition of I Sigma I

[ANDY DODDS]

Hi,

does anyone have a definition of I Sigma I please.  Any definitions
that i have found are not very informative for novices.


thanks

andy

Re: [ccp4bb] definition of I Sigma I

[Anastassis Perrakis]

Hi -

I Sigma I means nothing.

I/sigma(I) is the average intensity of a group of reflections  
divided by the average standard deviation (sigma) of the same group of  
reflections. Usually its reported per resolution shell, groups of  
reflections within thin shells of resolution.


I/sigma(I) is the intensity divided by the standard deviation  
(sigma) of a reflection, averaged for a group of reflections. Its also  
usually reported per resolution shell, groups of reflections within  
thin shells of resolution.


Both report signal over noise, and in many (most?) publications its  
unclear which one is reported. They are similar but not the same.


Hope this helps.

A.

On 10 Dec 2008, at 23:14, ANDY DODDS wrote:


Hi,

does anyone have a definition of I Sigma I please.  Any definitions
that i have found are not very informative for novices.


thanks

andy