Re: [ccp4bb]: Estimate Anormalous Signal-to-Noise ratio

["Eleanor J. Dodson" <ccp4@ysbl.york.ac.uk>]

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Yong Xiong wrote:
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> Dear all, does any one know/have a program/jiffy to estimate the anormalous signal-to-noise ratio by comparing the sigma values of centric and
> acentric reflections? Seems all the popular scaling programs, (and the ccp4 mtz/sf utilities) don't have this information. I know BC Wang is
> advocating this idea but I could not find out any information on their program. Any comments about the reliability of this procedure?
> 
> Thanks!
> 
> Yong


 Well - the criteria I use are:

a) Analysis of centric and acentric normal probablities for the diffs
between F(+) and F(-) given at the end of scaleit.summary
 ( If you ask the GUI to analysis anomalous signals for a MAD or SAD
expt it gives you this..) It is rather dependent on how you processed
the centric reflns, but gives some idea of signal.


b) the best is the correlation betwen anomalous differences from
different wave lengths. If this isnt > 0.2 george Sheldrick says  you
havreent got a signal.

 Eleanor
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Eleanor J.Dodson, York Structural Biology Laboratory,
                  Chemistry Department, 
                  University of York, Y01 5DD Heslington, U.K.
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