Positivism vs Realism
tdib at UMICH.EDU
Mon Dec 15 08:58:18 CST 1997
James Francis Lyons-Weiler wrote:
>>Tell me, have you sampled published morphological datasets to
>>determine what percentage are reporting insignificant conguence, by
> No, I haven't - because I don't know what the result would
I'll tell you what it would mean. It would provide an indication of
whether morphological datasets are ever, or very often of
questionable significance (by your standards); a question that you
seem constantly to raise. You ask me if I would put forward a tree
which is judged to be indistinguisahble from one generated by random
data; as if this were a pressing concern. And I would like to know
how often you have found it to be a real concern - in morphological
studies. As you know, morphological studies are done on datasets
which represent many years of careful study; on homology hypotheses
which are well tested in the biological realm. As you also know, many
morphological systematists tend to see these "tests against
randomness" to be a little besides the point. Now for molecular
sequences, where there is not much, beyond alignment, to be
studied,,there is a general sense that perhaps these tests have
meaning. I think these are very interesting questions.
> The test is designed for the specific case, one
> matrix at a time.
so what? I am just wondering what proportion of datasets, considered
one at a time, are found to be presenting insignificant results.
> I have found published morphological
> data sets for which the test reveals sources of incongruence,
> including long edges, but I don't find the number of
> instances a very interesting question. It could be high,
> or low.
Why not?? It speaks to the efficacy of the procedures. Something you
certinly seem interested in discussing a lot.
> A question you didn't ask that I find more
> interesting is how many morphological data sets can I find
> for which the application of the tests improves the
> degree of congruence by pinpointing sources of noise -
> but that work is underway.
Improve the degree of congruence by pinpointing noise - I wonder what
that means, other than what parsimony does. Parsimony of course,
finds congruence. Noise is incongruence. You are imposing some new
standard here, right? You are finding a reason to dismiss character
matches even if they are congruent (i.e. even if they are retained by
parsimony - else how would you be doing anything different).
Interesting,,,,,,what if they are real though...?
> We can't expect all regimes of character
> and taxon sampling to yield matrices that are not misleading.
Nor can we expect statistical regularities to inform us when
particular data points are misleading,,,,,right?
your fellow hackles-on-the-pious raiser,
Tom DiBenedetto http://www-personal.umich.edu/~tdib/
Fish Division tdib at umich.edu
University of Michigan Museum of Zoology
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