On Mon, Oct 27, 2014 at 1:19 PM, George Devaniranjan <devaniranjan@gmail.com> wrote:

Would you define "significant" for me (as you see it of course)?

Pavel's definition:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2906258/

"...the difference between R factors computed using the different methods is typically less than 0.01%."

I think this is probably a typo and it is supposed to mean "1%" or "0.01", which would have been my estimate. Certainly differences below 0.005 are hardly worth noticing, and below 0.001 is statistical noise. Differences above 0.01 are more worrisome (although not entirely unheard of).

I am NOT a X-ray crystallographer but I was intrigued by this post. I have RE-refined structures and have seen R/R (Free) go up say by 0.4
Say from 0.110 to 0.150
Would you say that is significant for high resolution structures ?

Yes. It may reflect a sub-optimal refinement strategy, although I have seen this happen occasionally when re-refining (in Phenix) an ultra-high-resolution structure previously refined with SHELX.

-Nat