Outgroup selection

[aj49]

Forgive my ignorance, but I am writing to ask the members of taxacom for
help finding published papers that deal with the selection of outgroups and
study taxa in cladistic analysis of morphological data.  Specifically, I am
interested in whether anybody has examined the effect of outgroup choice on
results, and the effect on tree topology of excluding taxa or sets thereof
from analyses.

I would very much appreciate any references anybody may be able to point me
to.  Thanks!