I think if you want to target systematic errors you need to repeat the
measurements in different orientations - twiddle the arcs to get diff
absorbtion etc..
If you have high enough redundancy in diff orientations the SigmFs
estimated should be related to the scatter of observations..
Eleanor
Ulrich Genick wrote:
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Hi,
a quick question for the data processing jocks.
How much do systematic and random errors contribute to the
final sigmaF of a structure factor.
Basically, I want to do some computation that involves the Fs from
two consecutive data sets taken
on the same crystal and in order to do
error propagation I need to know, if the sigmaF's for the same
reflection in the final merged data sets
are independent or correlated. My gut feeling is that the errors will
be mostly independent.
I am positive somebody, (or probably a lot of people) know the answer
to this question and it is
probably written up somewhere in some old paper on scaling heavy
metal derivatives.
Here is the scenario, I take a crystal and collect the same data set
twice. Both data sets
have a decent redundancy of 3-5 and there is no noticeable radiation-
induced decay.
Will the sigmaFs of the two data sets overestimate the difference
between
the two data sets (i.e. is there systematic error that is reproduced
between the data sets)
or will the sigmaF predict the difference between the two data sets
correctly (i.e. the error is random).
I am sure the answer will depend on the redundancy of the data sets,
the quality of the crystals, the
resolution the stability of the beam etc. etc. My question is what
will happen on average.
Cheers,
Ulrich
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