On Mon, 10 Apr 2000, Rich Ulrich wrote:
---------------------- >8 -----------------------
> > the term 'null' means a hypothesis that is the straw dog case ... for which
> > we are hoping that sample data will allow us to NULLIFY ...
>
> - this seemed okay in the first sentence. However, I think that
> "straw dog case" is what I would call "straw man argument" and that
> is *not* the quality of argument of the null. The point-null is
> always false, but we state the null so that it is "reasonable" to
> accept it, or to require data in order to reject it.
>
---------------------- >8 -----------------------
Rich, I do not agree that the point-null is always false. But I guess it
depends on how you define "point-null". Bob Frick has some very
interesting things to say about all of this. For example, the following
is taken from his 1995 Memory & Cognition paper (Vol 23, pp. 132-138),
"Accepting the null hypothesis":
<start quote>
To put this argument another way, suppose the question is whether one
variable influences another. This is a discrete probability space with
only two answers: yes or no. Therefore, it is natural that both answers
receive a nonzero probability. Now suppose the question is changed into
one concerning the size of the effect. This creates a continuous
probability space, with the possible answer being any of an infinite
number of real numbers and each one of these real numbers receiving an
essentially zero probability. A natural tendency is to include 0 in this
continuous probability space and assign it an essentially zero
probability. However, the "no" answer, which corresponds to a size of
zero, does not change probability just because the question is phrased
differently. Therefore, it still has its nonzero probability; only the
nonzero probability of the "yes" answer is spread over the real numbers.
<end quote>
Frick's 1996 paper in Psychological Methods (Vol 1, pp. 379-390),
"The appropriate use of null hypothesis testing" is also very interesting
and topical. From the abstract of that paper: "This article explores
when and why [null hypothesis testing] is appropriate. Null hypothesis
testing is insufficient when the size of effect is important, but is ideal
for testing ordinal claims relating the order of conditions, which are
common in psychology."
Cheers,
Bruce
--
Bruce Weaver
[EMAIL PROTECTED]
http://www.angelfire.com/wv/bwhomedir/
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