Manfred S. Weiss wrote:
That's not quite correct. If N goes to infinity, i.e. at high or very high
data multiplicity Rmerge approaches Rmeas (Rrim).
At this point it does not matter whether you write Rmerge or Rmeas
equals 0.8 * sd(I) / I
For low multiplicity
Rrim (or Rmeas) = 0.8*sd(i)/I
For more than one reflection, would that be
Rrim (or Rmeas) = 0.8*<sd(i)>/<I> ?
or is sd(i) same for all reflections?
is the correct expression.
Cheers, Manfred
On 16.04.2014 22:16, Bernhard Rupp wrote:
The 2006 Weiss expression - I guess from the context- is for a single
reflection h
measured N times (and then is identical to my 8-23) while (8-24) is valid for
the Rmerge
(defined in 8-15) of averaging over a shell with h reflections each measured N
times ,
which also explains why the two related expressions in aimless necessarily have
to be
different.
Somehow crystallographers historically invented their own linear merging
statistics
instead of 'standard' descriptive statistics like the standard error of the
mean...still
an unresolved mess see the papers/threads on cc1/2, cc* etc...
Best, BR
-----Original Message-----
From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Roberto
Battistutta
Sent: Wednesday, April 16, 2014 5:09 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: [ccp4bb] Rmerge, Rmeas, I/sigma, Mn(I/sd)
Hi,
in the Rupp book the following relation is reported (on pag 415):
Rmerge 0.8/<I/s(I)>
referring to a relation of "the linear merging R-value with the signal-to-noise
ratio".
in a 2006 CCP4bb, Manfred Weiss reported:
Rrim (or Rmeas) = 0.8*sd(i)/I
so,
First question: is it Rmerge or Rmeas (Rrim) that we are dealing with?
Second question: at the denominator (of the Rupp way to write), it is the
aimless
Mn(I/sd) (usually indicated as the real signal-to-noise ratio) or the aimless
I/sigma
(very different from Mn(I/sd) with high redundancy)?
Thank you very much for the clarification.
Best,
Roberto.
Roberto Battistutta
Associate Professor
Department of Chemistry
University of Padua
via Marzolo 1, 35131 Padova - ITALY
tel. +39.049.827.5262
fax. +39.049.827.5829
roberto.battistu...@unipd.it
www.chimica.unipd.it/roberto.battistutta/
VIMM (Venetian Institute of Molecular Medicine) via Orus 2, 35129 Padova -
ITALY tel.
+39.049.7923.236 fax +39.049.7923.250 www.vimm.it
--
Dr. Manfred. S. Weiss
Helmholtz-Zentrum Berlin für Materialien und Energie
Macromolecular Crystallography (HZB-MX)
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