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From: "Bonnie Blackwell, x 3332" <firstname.lastname@example.org>
> Stan's posting (9612.03) oversimplified the problem of picking 75%
> f the lancian species. No one could imagine that the selection was
> truly random.
True, not entirely random. But I am not yet convinced that the data
can be *distinguished* from an essentially random process. (Which
is a slightly different statement).
> And each group would have experienced different
> selection (extinction) pressures as a whole, as would each family
> and order and so forth. The problem is in picking 75% overall, but
> maybe only 30% mammals, 100% dinos and pteros, 60% birds, etc....
This is exactly the result one might get from a random process.
That is my main point - the particular distribution of extinctions
may not be any different than what would be produced by a random
The issue here is one of using the data to support a model. If the
data is indecisive, the random model cannot be rejected.
My suspicion is that there was some non-random component - some bias -
in the extinctions, but that there was also a substantial stochastic
component. This is what I really mean when I say that the dinosaurs
were not *specifically* singled out by the extinction mechanism. One
of the other groups with, say, >= 50% extinction might equally well
have died out.
> It may be (or more likely is not) rather random within narrowly
> defined groups, but certainly not across the board.
Actually, I think it is *very* likely that it was partially random
within fairly ecological groups. How to *test* this model against
the data, however, is a difficult issue.
Now, if a proper statistical analysis of the model I presented compared
against the actual data shows a stistically significant variance from
the expected pattern, then the *broad* stochastic model can be rejected.
Of course this still leaves various combination models.
The peace of God be with you.