Hi Kay,
from my experience with refinement at resolutions higher than ~1.0A:
I usually see the gaps Rfree-Rwork ranging from 0.5 to 1.5%. This small
difference could be a result of trapping in a local minimum because of
huge amount of data at that resolutions. Reducing the amount of data by
refining in resolution zone like 0.7 - 0.9 A gave me a gap Rfree-Rwork ~ 5%.
Just my observations ...
Cheers,
Pavel.
On 11/15/2007 8:41 AM, Kay Diederichs wrote:
Dear crystallographers,
today I explained to a student that I believe that the difference of
R_work and R_free should decrease as a function of resolution, because
at high resolution there is less danger of overfitting, whereas at low
resolution one is always overfitting to some extent. I'd say this
should be true at least in absolute terms, but probably even in
relative terms: for example, for a 1.5A structure I'd expect
R_work/R_free= 14%/16%, whereas at 3A I'd expect 28%/35%.
I believe that I saw plots (maybe in a link given in a posting on
CCP4BB) obtained for structures from the PDB, which confirmed this
hypothesis. But I've been googling and searching through postings now
for quite some while, and cannot seem to find anything to that effect.
Does anybody have a pointer to an analysis of this effect?
thanks,
Kay
P.S. Would be good to put this into the CCP4 Wiki article on R-factors
