I'm afraid Gerard an Ian between them have left me a bit confused with
conflicting statements:
On 04/06/2015 15:29, Gerard Bricogne wrote:
<snip>
In order to guard the detection of putative bound fragments against the evils
of model bias, it is very important to ensure that the refinement of each
complex against data collected on it does not treat as free any reflections
that were part of the working set in the refinement of the apo structure.
<snip>
On 04/06/2015 17:34, Ian Tickle wrote:
<snip>
So I suspect that most of our efforts in maintaining common free R
flags are for nothing; however it saves arguments with referees when
it comes to publication!
<snip>
I also remember conversations and even BB threads that made me conclude
that it did NOT matter to have the same Rfree set for independent
datasets (e.g. different crystals). I confess I don't remember the
arguments, only the relief at not having to bother with all the
bookkeeping faff Gerard outlines and Ian describes.
So: could someone explain in detail why this matters (or why not), and
is there a URL to the evidence (paper or anything else) in either
direction?
(As far as I remember, the argument went that identical free sets were
unnecessary even for exactly isomorphous crystals. Something like
this: model bias is not a big deal when the model has largely
converged, and that's what you have for molecular substitution (as Jim
Pflugrath calls it). In addition, even a weakly binding fragment
compounds produces intensity perturbations large enough to make model
bias irrelevant.)
phx
