In my opinion Rpim is not related directly to anomalous signal, so perhaps that 
is why there is some confusion.

Also I think some folks confused Rpim with Rrim.  The latter is also called 
Rmeas.  But once again, these are not related directly to anomalous signal.  I 
do not find Rpim very useful for anything since when the data has high 
multiplicity Rpim gets very low, but as Michael Blum told me, "Precision does 
not trump accuracy."  I would personally rather have accurate data than highly 
redundant but inaccurate data.

I like to look at the deltaF / sigma(deltaF) value reported by SHELXC and other 
programs, where deltaF is ||F+| - |F-||.
This might also be called <d"/sig>.  There are other things to look at as well.


From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Vijayakumar.B 
Sent: Tuesday, September 18, 2012 4:36 AM
Subject: [ccp4bb] Rpim and how its related to anomalous signal

Dear CCP4BB users,

I am very much interested to work in Anomalous scattering technique for 
macromolecular structure determination. I have already gone through some 
literature in which they have explained about a parameter called “Rpim”.  I am 
little bit confused about Rpim values.

Can anyone tell me about the use of this parameter in structure determination 
by anomalous techniques and how Rpim is related to anomalous signal?  Thanks in 

With kind regards

B. Vijayakumar

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