Hi Andrea, Any choice you make about a resolution cut-off based on a rule of thumb can be called into question by a referee who uses a different rule of thumb. So if you choose a metric + cut-off that is anything less than very conservative (say I/sigI > 1), you have to be able to defend your choice either with a reference or with evidence from experiments. This is where the 'paired refinement' of the Karplus and Diederichs paper kicks in: you can show that you can get useful information out of the extra high resolution reflections by comparing refinement results.
So what you can do is first solve your structure, build and refine using a conservative resolution cut-off. Once you are nearing the final stages of the process you can gradually go for higher resolutions using the paired refinement procedure. That way you have some results to support you choice of resolution cut-off. Who knows, when you reach the best resolution cut-off you may be able to add some more details to your structure model, that you would have missed otherwise. If you think that doing the paired refinement is too much work, you can try PDB_REDO. If you give it a PDB file with a resolution cut-off in REMARK 2 or 3 lower than the maximal resolution of your reflection file, it will automatically use paired refinement to find the best resolution cut-off (yes, this is a self-plug!). HTH, Robbie Joosten > -----Original Message----- > From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of > Andrea Edwards > Sent: Thursday, June 13, 2013 17:15 > To: CCP4BB@JISCMAIL.AC.UK > Subject: [ccp4bb] Concerns about statistics > > Hello group, > I have some rather (embarrassingly) basic questions to ask. Mainly.. when > deciding the resolution limit, which statistics are the most important? I have > always been taught that the highest resolution bin should be chosen with > I/sig no less than 2.0, Rmerg no less than 40%, and %Completeness should be > as high as possible. However, I am currently encountered with a set of > statistics that are clearly outside this criteria. Is it acceptable cut off > resolution > using I/sig as low as 1.5 as long as the completeness is greater than 75%? > Another way to put this.. if % completeness is the new criteria for choosing > your resolution limit (instead of Rmerg or I/sig), then what %completeness is > too low to be considered? Also, I am aware that Rmerg increases with > redundancy, is it acceptable to report Rmerg (or Rsym) at 66% and 98% with > redundancy at 3.8 and 2.4 for the highest resolution bin of these crystals? I > appreciate any comments. > -A
