Hi Ethan,
I would place the expected resolution break-even point at more like > 1.2 - 1.3 A. But that's only an expectation, not a rule to rely on. > You should justify anisotropic refinement of a structure on the basis > of its own particular model and measured data. Robbie Joosten has > already pointed out that you can use the PDB-Redo scripts to test > whether individual anisotropic ADPs are justified. > when it comes to a point when a choice of refinement strategy cannot be uniquely and reliably chosen based on theoretical considerations, that opens a great opportunity for endless perennial discussions like this. My point was that if you are lucky and there isn't many options (in this case there are only two: iso vs aniso!) there is an easier, quicker and robust alternative: simply try both and that will give your THE answer. Perhaps not very scientific (no monster formula derived) but quick, easy and robust! > > - higher than 1.2A: all anisotropic (macromolelcule, water, ligands) > > - lower than 1.7A: all isotropic; > > - 1.5-1.7A is a grey area where there is only one single way to know for > > sure: try both (isotropic and anisotropic) and see which one works best. > > I realize "works best" is a broad term, but I would say Rwork, Rfree, > > Rfree-Rwork and values of refined anisotropic ADPs should be enough to > make > > a decision. > > Unfortunately, Rfree cannot be used reliably for this purpose. > Yes, Rfree cannot be used for this purpose reliably, very true. This is exactly why I wrote above ".. Rwork, Rfree, Rfree-Rwork *and values of refined anisotropic ADPs* should be enough to make a decision." My understanding is that your "To B.." method is one of possible ways of looking at the values of refined anisotropic B-factors. All the best, Pavel
