 |
 |
Hmm, I used to think I understood this, but I'm feeling a bit dim right now. On 25/08/2011 11:07, Ian Tickle wrote: > Since the target function in MX refinement is the total likelihood > (working set + restraints), there's no reason whatsoever why any > another function, such as Rfree & LLfree, should have an extremum at > the same point in parameter space as the target function. This is self-evident; what is not obvious is why the target function should be having the final word. Wasn't the word "over-refinement" introduced to describe exactly this: that the target function was wrong? Isn't this the purpose of cross-validation, to use an independent measure to judge when the refinement is /not/ producing the "best" model? > Rfree is particular is problematic because it is unweighted, so poorly > measured reflections in the test set are going to have a > disproportionate influence on the result (e.g. see /Acta Cryst./ > (1970). A*26*, 162). This may be true; but as it is independent of refinement, is it not nevertheless the only measure I should trust? Or maybe what you intended to say: only trust refinements for which Rfree decreases monotonically, because only then do you have a valid choice of parameters. phx.