[EMAIL PROTECTED] wrote (in part):
> I'm saying that the entire concept of practical significance is not only
> subjective, but limited to the extent of current knowledge. You may
> regard a 0.01% effect at this point in time as a trivial and (virtually)
> artifactual byproduct of hypothesis testing. But if proper controls are
> in place, then to do so is tantamount to ignoring an effect that, on the
> balance of probabilities shouldn't be there if all things were equal. I
> think we need to be cautious in ascribing effects as having little
> practical significance and hence using this as an argument against
> hypothesis testing.
"Practical significance" is relevant if and only if there is some
"practice" involved - that is to say, if a real-world decision is going
to be based on the data. Such a decision _must_ be based on current
knowledge, for want of any other; but if the data are preserved, a
different decision can be based on them in the future if more is known
then.
(BTW: If a decision *is* to be made, a risk/benefit approach would seem
more appropriate. Yes, it probably involves subjective decisions; but
using fixed-level hypothesis testing to avoid that is a little like
saying "as I might not choose exactly the right size of screwdriver I
shall hit the screw with a hammer". If we do take the risks and
benefits into account in "choosing a p-value", we are not really doing a
classical hypothesis test, even though the calculations may coincide.)
However, if a real-world decision is *not* going to be made, there is
usually no need to fit the interpretation of marginal data into the
Procrustean bed of dichotomous interpretation (which is the
_raison_d'etre_ of the hypothesis test). Until there is overwhelming
data one way or the other, our knowledge of the situation is in shades
of gray, and representing it in black and white is a loss of
information.
-Robert Dawson
=================================================================
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
http://jse.stat.ncsu.edu/
=================================================================
