I take the point about a tendency in those days to apply sigma cutoffs to get lower R values, which were erroneously expected to indicate better structures. I wonder how many of us remember this paper by Arnberg et al (1979) Acta Cryst A35, 497-499, where it is shown for (small molecule) structures that had been refined with only reflections I>3*sigma(I) that the models were degraded by leaving out weak data (although the R factors looked better of course).
Arnberg et al took published structures and showed the refined models got better when the weak data were included. The best bit, I think, was when they went on to demonstrate successful refinement of a structure using ONLY the weak data where I<3*sigma(I) and ignoring all the strong ones. This shows, as was alluded to earlier in the discussion, that a weak reflection puts a powerful constraint on a refinement, especially if there are other stronger reflections in the same resolution range. --------------------------------------------------------------------------- | Simon E.V. Phillips | --------------------------------------------------------------------------- | Director, Research Complex at Harwell (RCaH) | | Rutherford Appleton Laboratory | | Harwell Science and Innovation Campus | | Didcot | | Oxon OX11 0FA | | United Kingdom | | Email: simon.phill...@rc-harwell.ac.uk | | Tel: +44 (0)1235 567701 | | +44 (0)1235 567700 (sec) | | +44 (0)7884 436011 (mobile) | | www.rc-harwell.ac.uk | --------------------------------------------------------------------------- | Astbury Centre for Structural Molecular Biology | | Institute of Molecular and Cellular Biology | | University of LEEDS | | LEEDS LS2 9JT | | United Kingdom | | Email: s.e.v.phill...@leeds.ac.uk | | Tel: +44 (0)113 343 3027 | | WWW: http://www.astbury.leeds.ac.uk/People/staffpage.php?StaffID=SEVP | ---------------------------------------------------------------------------
