My understanding is(was) that Rsym refers to the merging of
symmetry-related reflections during scaling whereas Rmerge refers,
broadly, to any data merging process, but originally means merging of
reflection with the same (hkl). Rcryst then should refer to the merging
of data from different crystals. The final number reported by, say,
scalepack will thus be both Rsym and Rmerge, but is referred to as
Rmerge because Rsym is also an instance of Rmerge, at least
semantically. I understand the usefulness of Rsym is limited to the
process of space group identification, whereas overall Rmerge reflects
(somewhat and in clearly relative fashion) upon the quality of your data.
At risk of injecting more controversy to this fairly benign discussion,
let me quote Daniel Gewirth:
"In practice, there are two ways of assessing the high resolution limit
of diffraction. The first is the ratio of the intensity to the error of
the intensity, i.e. I/σ. The second way, which is traditional but
inferior, is the agreement between symmetry related reflections, i.e.
Rmerge."
So Rmerge is Rsym? What makes this question somewhat irrelevant,
however, is this:
"One of the drawbacks of using Rmerge as a measure of the quality of a
data set is that it can be
intentionally and unintentionally manipulated. "
Cheers,
Ed.
--
Edwin Pozharski, PhD, Assistant Professor
University of Maryland, Baltimore
----------------------------------------------
When the Way is forgotten duty and justice appear;
Then knowledge and wisdom are born along with hypocrisy.
When harmonious relationships dissolve then respect and devotion arise;
When a nation falls to chaos then loyalty and patriotism are born.
------------------------------ / Lao Tse /
