On 14 Mar 2001 08:33:29 -0800, [EMAIL PROTECTED] (dennis roberts) wrote:
[ ... ]
> however, i think that we definitely need some standardization and revamping
> when it comes to using terms like 1 and 2 tailed tests ...
> the term "tail" ... either 1 tailed or 2 tailed ... should ONLY be used in
> connection with what the test statistic that you have decided to use ...
> naturally asks you to do with respect to deciding on critical values ...
[ snip, much]
I agree, that we need to be careful... Maybe we need some
conventions? I was less sure, until I read the following:
>
> when we do a simple ANOVA ... this should be called a 1 tailed test ... no
> matter what your research predictions are ... when we use chi square on a
> contingency table ... it should be called a 1 tailed test ... no matter how
> you think the direction of the relationship should go
Ooh, I don't like it, I don't like any mention of "1" right here, in
either case. Sure, "1" is true, but it is mainly misleading and
irrelevant, right?
That ANOVA is inherently a 2-sided test. So is the traditional 2x2
contingency table. That is because, sides refer to hypotheses.
The t-test is inherently 1-sided, like a z: only the large,
plus-sign values have small p's. But some people *always*
refer to 2-sided probabilities of z and t. That is, they use a
two-tailed t-test, (two-tailed z) which is equivalent to using an
ANOVA F (chi-squared with 1 d.f.).
The default-test of any sort, I suggest, is "one-tailed" and
we get p from its Cumulative Distribution Function; and
1-tailed does not have to be mentioned. If we pool the tails,
that requires special notice, and we should specify that the t
is "two-tailed."
[ snip, more details; including 't-test' suggestions that
are contrary to what I just wrote.]
--
Rich Ulrich, [EMAIL PROTECTED]
http://www.pitt.edu/~wpilib/index.html
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