Yes higher R factors is the usual reason people don't like I-based refinement!
Anyway, refining against Is doesn't solve the problem, it only postpones it: you still need the Fs for maps! (though errors in Fs may be less critical then). -- Ian On 20 June 2013 17:20, Dale Tronrud <det...@uoxray.uoregon.edu> wrote: > If you are refining against F's you have to find some way to avoid > calculating the square root of a negative number. That is why people > have historically rejected negative I's and why Truncate and cTruncate > were invented. > > When refining against I, the calculation of (Iobs - Icalc)^2 couldn't > care less if Iobs happens to be negative. > > As for why people still refine against F... When I was distributing > a refinement package it could refine against I but no one wanted to do > that. The "R values" ended up higher, but they were looking at R > values calculated from F's. Of course the F based R values are lower > when you refine against F's, that means nothing. > > If we could get the PDB to report both the F and I based R values > for all models maybe we could get a start toward moving to intensity > refinement. > > Dale Tronrud > > > On 06/20/2013 09:06 AM, Douglas Theobald wrote: > >> Just trying to understand the basic issues here. How could refining >> directly against intensities solve the fundamental problem of negative >> intensity values? >> >> >> On Jun 20, 2013, at 11:34 AM, Bernhard Rupp <hofkristall...@gmail.com> >> wrote: >> >> As a maybe better alternative, we should (once again) consider to refine >>>> against intensities (and I guess George Sheldrick would agree here). >>>> >>> >>> I have a simple question - what exactly, short of some sort of historic >>> inertia (or memory lapse), is the reason NOT to refine against intensities? >>> >>> Best, BR >>> >>
