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
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:[log in to unmask]] On Behalf Of Roberto Battistutta
> Sent: Wednesday, April 16, 2014 5:09 PM
> To: [log in to unmask]
> 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
> [log in to unmask]
> 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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