Graeme wrote: "... Rpim is much more instructive. ... as each of these tells something different."
I have to ask: "Why is Rpim much more instructive? I'm trying to figure this out still. Can one please summarize what are best practices with all these numbers and how each of these tells something different?" Another problem that I see is that folks can adjust their sigmas many different ways without knowing they have adjusted their sigmas. And they can be adjusted incorrectly when they are adjusted. BTW, Graeme is correct about lots of multiple low I/sigI observations for each Bragg reflection in a resolution shell will lead to 100% (or higher) Rmerge with <I/sigI> of 3. This assumes no systematic errors and only randomly distributed random errors (a rare if not impossible situation, I would think). I will defer to others about what the relevance of that is. Thanks for any insights, Jim ________________________________ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Graeme Winter [graeme.win...@gmail.com] Sent: Tuesday, November 19, 2013 2:02 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] 100% Rmerge in high resolution shell Usually this means that you have relatively high multiplicity, which give-or-take improves the I/sig(I) by sqrt(m) where m is the multiplicity, but also increases the Rmerge. For any given narrow shell of reflections, Rmerge ~ 0.8 / unmerged(I/sig(I)) merged(I/sig(I)) ~ sqrt(m) * unmerged(I/sig(I)) So it is perfectly possible to have unmerged I/sig(I) of 0.8 which will give you an Rmerge of around 1.0, and have I/sig(I) (merged) around 3, by having multiplciity 14 or so. I suggest that this is the case: if it is much lower than this there is something odd going on. For the merged I/sig(I) Rpim is much more instructive. I'd love it if people reported merged and unmerged I/sig(I), Rmerge, Rmeas, Rpim, CC1/2, ... as each of these tells something different. Best wishes, Graeme Possibly useful papers: http://www.nature.com/nsmb/journal/v4/n4/abs/nsb0497-269.html http://scripts.iucr.org/cgi-bin/paper?he0191 http://scripts.iucr.org/cgi-bin/paper?he0268 On 19 November 2013 06:43, Shanti Pal Gangwar <gangwar...@gmail.com<mailto:gangwar...@gmail.com>> wrote: Dear All Can anyone explain the meaning and relevance of data when the Rmerge is 100% in high resolution shell and I/sig(I) is 3. Thanks -- ******************** regards Shanti Pal Gangwar School of Life Sciences Jawaharlal Nehru University New Delhi-110067 India Email:gangwar...@gmail.com<mailto:email%3agangwar...@gmail.com>
