Shane Atwell wrote:
Could someone point me to some standards for data quality, especially
for publishing structures? I'm wondering in particular about highest
shell completeness, multiplicity, sigma and Rmerge.
A co-worker pointed me to a '97 article by Kleywegt and Jones:
_http://xray.bmc.uu.se/gerard/gmrp/gmrp.html_
"To decide at which shell to cut off the resolution, we nowadays tend to
use the following criteria for the highest shell: completeness > 80 %,
multiplicity > 2, more than 60 % of the reflections with I > 3 sigma(I),
and Rmerge < 40 %. In our opinion, it is better to have a good 1.8 Å
structure, than a poor 1.637 Å structure."
Are these recommendations still valid with maximum likelihood methods?
We tend to use more data, especially in terms of the Rmerge and sigma
cuttoff.
Thanks in advance,
*Shane Atwell*
Hi Shane,
I definately no longer support the conclusions from that 1997 paper and
I think Gerard probably has adjusted his thoughts on this matter as
well. Leaving out the data beyond 1.8A (in the example above) only makes
sense if there is no information in those data. Completeness and
multiplicity are not direct measures of data quality and the 60%
I>3sigma and Rmerge <40% criteria are too strict to my liking. I prefer
to look at I/SigI mostly, and as a reviewer I have no problems with
highest resolution shell stats with I/SigI anywhere in the 1.5-2.5
range. I won't complain about higher I/SigI values if done for the right
reasons (phasing data sets being the most common), but will say
something if they state their crystals diffract to 2.5A if the I/SigI in
the highest resolution shell is, let's say, 5. Their crystals don't
diffract to 2.5A, they just didn't let the crystals diffract to their
full potential. You can't really reject papers for that reason, but
there appears to be a conservative epidemic when it comes to restricting
the resolution of the data set.
Bart
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University of Alberta
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