On 30 Mar 2009, at 20:30, James Holton wrote:
Frank von Delft wrote:
So, what statistic do we want to look at? That depends on what you
are trying to do with the data. There is no way for Phil to know
this, so it is good that he prints out lots of different
statistics. That said, when talking about the data quality
requirements for structure solution by MAD/SAD, I suggest looking at
I/sigma(I) where:
I - merged intensity (proportional to photons) assigned to a
reciprocal lattice point (hkl index)
Does ANY program print this out...?
SCALA calls this "Mn(I/sd)". Sounds like d*TREK calls it "I/sig avg".
That is my understanding as well.
With HKL you compute it "by hand" from the average I and average
"error".
hmmm ... from "error" or from "stat."? Should chi^2 be 1 first?
Not sure about XDS...
Confusingly, XDS calls that I/SIGMA from what I understand (which as I
said before is NOT what SCALA calls I/sigma)
Since we only use XDS and (mostly) SCALA in the lab, that is very
confusing.
I am pretty sure btw that I have myself -wrongly- quoted I/sigma as
being <I/sigma(I)> in at least 3-4 papers.
And I can bet I am not the only one that did so.
<I>/sigma<I> and <I/sigma(I)> are in my view more deterministic labels
and will get safer on their way to "Table 1".
Tassos
-James Holton
MAD Scientist
