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: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
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