Re: [ccp4bb] I/sigma continued

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

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Subject: Re: I/sigma continued
From: James Holton JMHolton {- at -} LBL {- dot -} GOV
Date: 2009-03-30

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Subject: Re: I/sigma continued
From: "Miller, Mitchell D {- dot -} " mmiller {- at -} SLAC {- dot -} STANFORD {- dot -} EDU
Date: 2009-03-30

Subject: Re: I/sigma continued
From: Anastassis Perrakis a {- dot -} perrakis {- at -} NKI {- dot -} NL
Date: 2009-03-30

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 in at least 3-4 papers.
And I can bet I am not the only one that did so.

/sigma and are in my view more deterministic labels
and will get safer on their way to "Table 1".

Tassos

>
>
> -James Holton
> MAD Scientist

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Subject: Re: I/sigma continued
From: James Holton JMHolton {- at -} LBL {- dot -} GOV
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Subject: Re: I/sigma continued
From: "Miller, Mitchell D {- dot -} " mmiller {- at -} SLAC {- dot -} STANFORD {- dot -} EDU
Date: 2009-03-30