> 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 two crystallographic models give the same results if you
throw out the datapoints which only have background contributions? The
"reducio ad absurdum" would be to use Rwp from a multipattern fit where
only one pattern contains the phase of interest. Maybe that's statistically
valid if some of the least squares parameters depend on all of the patterns?
Bill David's work on deriving the number of independent peaks in a powder
pattern seems to offer a route to significance testing for different
crytallographic models (J.Appl.Cryst.(1999) 32:654). Perhaps it just adds
to the confusion.
Cheers,
Jon Wright
