Dear Andrea, Checking the quality of electron density maps has been correctly mentioned as one adds more data.
In chemical crystallography one can monitor the bond distance and angles sigmas ie until adding more data at ever higher resolution causes them to deteriorate in quality. The equivalent in protein crystallography can be done if one has sufficient resolution for the least squares model refinement full matrix inversion to work. Alternatively, at poorer resolutions than that, you can monitor if the Cruickshank-Blow Diffraction Precision Index (DPI) improves or not as more data are steadily added to your model refinements. To quote the resolution in your article at which I/sigI crosses 2, whilst not cutting the data at that point, can assist the reader in knowing the data quality you have worked with. Making the raw diffraction data images available would make things totally clear to the reader. Best wishes, John Professor John R Helliwell DSc On Thu, Jun 13, 2013 at 4:15 PM, Andrea Edwards <edwar...@stanford.edu>wrote: > 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 > --
