Dear All,
the short paper by Gerard Kleywegt (ActaD 63, 939-940) treats an interesting subject (at least I think so...). I agree that what we are now doing in many cases is effectively refining against Rfree. For example, the standard CNS torsion angle refinement does n refinement trials with randomised starting points. If you then take the one with lowest Rfree (or let a script do this for you), you are biasing Rfree!
Therefore, his proposal to put an extra set of reflections in a dormant "vault" (R-sleep) sounds like a good idea to me. However, how would the "vault" be implemented to be effective? If left to the experimenter, it would be very tempting to check R-sleep once in a while (or often) during refinement, rendering it useless as an unbiased validator.
or am I being paranoid and too pessimistic?
Mark J. van Raaij
Unidad de Bioquímica Estructural
Dpto de Bioquímica, Facultad de Farmacia
and
Unidad de Rayos X, Edificio CACTUS
Universidad de Santiago
15782 Santiago de Compostela
Spain
