My preferred criterion is the half-dataset correlation coefficient output by Scala (an idea stolen from the EM guys): I tend to cut my data where this falls to not less than 0.5.
The good thing about this is that it is independent of the vagaries of <I/sigma> (or rather of the SD estimation) and has a more intuitive cutoff point than Rmeas (let alone Rmerge). It probably doesn't work well at low multiplicity and there is always a problem with anisotropy (I intend to do anisotropic analysis in future) That said, the exact resolution cut-off is not really important: if you refine & look at maps at say 2.6A vs. 2.5A (if that's around the potential cutoff), there is probably little significant difference Phil On 3 Mar 2011, at 15:34, Jim Pflugrath wrote: > As mentioned there is no I/sigmaI rule. Also you need to specify (and > correctly calculate) <I/sigmaI> and not <I>/<sigmaI>. > > A review of similar articles in the same journal will show what is typical > for the journal. I think you will find that the <I/sigmaI> cutoff varies. > This information can be used in your response to the reviewer as in, "A > review of actual published articles in the Journal shows that 75% (60 out of > 80) used an <I/sigmaI> cutoff of 2 for the resolution of the diffraction > data used in refinement. We respectfully believe that our cutoff of 2 > should be acceptable." > > -----Original Message----- > From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of > Roberto Battistutta > Sent: Thursday, March 03, 2011 5:30 AM > To: CCP4BB@JISCMAIL.AC.UK > Subject: [ccp4bb] I/sigmaI of >3.0 rule > > Dear all, > I got a reviewer comment that indicate the "need to refine the structures at > an appropriate resolution (I/sigmaI of >3.0), and re-submit the revised > coordinate files to the PDB for validation.". In the manuscript I present > some crystal structures determined by molecular replacement using the same > protein in a different space group as search model. Does anyone know the > origin or the theoretical basis of this "I/sigmaI >3.0" rule for an > appropriate resolution? > Thanks, > Bye, > Roberto. > > > Roberto Battistutta > Associate Professor > Department of Chemistry > University of Padua > via Marzolo 1, 35131 Padova - ITALY > tel. +39.049.8275265/67 > fax. +39.049.8275239 > roberto.battistu...@unipd.it > www.chimica.unipd.it/roberto.battistutta/ > VIMM (Venetian Institute of Molecular Medicine) via Orus 2, 35129 Padova - > ITALY tel. +39.049.7923236 fax +39.049.7923250 www.vimm.it
