On Mon, 10 Apr 2000, Robert Dawson wrote:
> Dennis Roberts wrote:
>
> > the term 'null' does NOT mean 0 (zero) ... though it is misconstrued that
> way
> > 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 ...
> > in some cases, the null happens to be 0 ... but in many cases, it does not
>
> It always means that _something_ is zero - as does just about any other
> algebraic or mathematical expression, after a little rearrangement into
> something logically equivalent . Moreover, in cases in which the null
My grandmother could have told me that the mean height for men and women
was not the same (zero difference). So based on prior evidence I
hypothesize that the actual difference is 3 inches (mu1 - mu2 = 3) and use
that for my null hypothesis. True, I can reduce this to a zero difference
version by using (mu1 - mu2) - 3 = 0 but do I really want to?
The problem is that Fisher ment "hypothesis to be nullified" and chose
the term "null" which has a mathematical meaning of "zero". This might
have been sensible in Fisher's applications where you wouldn't use a new
fertilizer unless it was different from nothing or some other
treatment. So null met both meanings.
But, I would argue that the height difference hypothesis is better
understood and more meaningful in its non-zero form. Perhaps we need to
refer to this hypothesis as the "test hypothesis".
> hypothesis has any prior credibility - as should always be the case - that
> "something" (eg, amount by which the IQ of the subject population differs
> from the standardized value of 100) is usually a sensible thing to study.
> And that thing can usually be thought of as "effect size".
>
> In the classic student blooper cases: "H0: mu = x bar" and "H0: mu
> equals the nearest round number to x bar" it isn't: and those tests should
> not be done.
>
> -Robert
>
>
*******************************************************************
Michael M. Granaas
Associate Professor [EMAIL PROTECTED]
Department of Psychology
University of South Dakota Phone: (605) 677-5295
Vermillion, SD 57069 FAX: (605) 677-6604
*******************************************************************
All views expressed are those of the author and do not necessarily
reflect those of the University of South Dakota, or the South
Dakota Board of Regents.
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