Bob Von Dreele wrote:
> >In that case even the single crystal data resulting from the integration
> >of images registred by an image plate are not strictly independent!!??
> >Information read from one pixel can depend on the information registred
> >in a neigbouring pixel.
>
> This would be true
observations are of the same object whether it be Bragg peaks
in a powder pattern or some other experimentally observed feature does not
make these observations "correlated". Bottom line is that Hamilton's test
is just as valid for powder data as it is for single crystal da
Bob Von Dreele wrote:
>The only exception to this is profile measurements taken on a film or >image plate
>where one observation may "bleed over" onto neighboring >ones. Only in that case are
>the profile points correlated with each >other in a statistical sense.
> Bob Von Dreele
In that case
>I would be careful with the Hamilton test in the case of powder
>diffraction, as your observations are not really independent from each
>other!
Strictly speaking this is not true. The individual measurements of powder
diffraction profile intensities are independent measurements. They do no
> The observations must be statistically independent, but need not be
> independent in the sense of what they physically measure.
It seems implicit from that sentence that the datapoints must be physically
measuring some aspect of the model, is that the case? For example: Does a
Hamilton test on
> I would be careful with the Hamilton test in the case of powder
> diffraction, as your observations are not really independent from each
> other!
This is a common misconception. (If not common, at least it was my
misconception until I had several long conversations with Ted Prince.)
The Hamilt
> I have obtained different R factors. Now I want to decide which is the
> most correct model. I have been suggested to use Hamilton R-factor
> ratio test.
I would be careful with the Hamilton test in the case of powder
diffraction, as your observations are not really independent from each
othe
Dear Nagesh
The R-factor is described in:
Volume 4 of International Tables for Crystallography section 4.2
pages 288 to 310.
if you have a look at Walter Hamilton's original paper:
Acta Crystallographica (1965), vol. 18, P502-510
you will see that it is based on the F-test which is
Dear Rietvelders,
I would appreciate your help in the following problem,
Even with a stoichiometric mixture of starting materials, NdBa2Cu3Oy is
known to form a solid solution of the type Nd1+xBa2-xCu3Oy(Non
stoichiometric). So a small amount of BaCO3 and CuO are expected to be the
impurities.
