The "black eye" comes not from the treatment of the observations, but from
the
treatment of the model. If you want to refine the same model against
lower
symmetry and/or unmerged data - go right ahead. I think the result will
not
usually be an improvement, but in some cases this may work around
systematic
artefacts in the data. What you should _not_ do is replicate the model to
produce multiple copies which are then refined as if they were
independent.
That amounts to doubling/tripling/whatever the number of model parameters.
Ethan
I think that when you say "as if they were independent," you are begging the
question. You could say that refining in higher symmetry treats the
molecules "as if they were the same." Further, it really assumes more to
posit that they are the same. Really the crux I think is weighing what
benefits one gets from treating the data in different ways. If one can know
somehow that the molecules when treated as p1 differ from each other only as
a function of experimental noise, there would be no reason to treat them as
p1. On the other hand, if somehow a few sidechains became systematically
different between molecules in the p1 cell, it *would* make sense to refine
in p1, no? (One could imagine an electric field around the crystal upon
freezing or whatever.)
Jacob Keller
