In article <[EMAIL PROTECTED]>,
Alan McLean <[EMAIL PROTECTED]> wrote:
>Will Hopkins wrote:
>> Responses to various folks. And to everyone touchy about one-tailed
>> tests, let me make it quite clear that I am only promoting them as a
>> way of making a sensible statement about probability. A two-tailed p
>> value has no real meaning, because no real effects are ever null. A
>> one-tailed p value, for a normally distributed statistic, does have a
>> real meaning, as I pointed out. But precision of
>> estimation--confidence limits--is paramount. Hypothesis testing is
>> passe.
...............................
< The only use for a test
<> statistic is to help you work out a confidence interval. Don't ever
<> report them in your papers.
>This is arguably the case for research matters when estimating/testing a
>mean - a confidence interval and a test are two ways of approaching the
>same thing. Even there, the hypothesis testing approach is a useful way
>of thinking. It is exactly the scientific method writ small. I also
>happen to think that all tests should be one tailed, but almost
>certainly not for the same reasons as Will's.
It is not the case even there. The scientific method is
concerned with making approximations, and it may be necessary
to accept approximations which clearly do not fit.
>In 'practical statistics' such as quality control, one is only
>interested if the sample mean is sufficiently close to what it should be
>that one can proceed as if it does equal what it should - that is,
>accept the null model and proceed - or not. If it is not, the 'true
>value' (meaningless phrase!) is of no interest, so obtaining a
>confidence interval is a waste of time. It could be done, but offers
>nothing.
This is correct, not only for quality control, but elsewhere.
The actual observations do not come from the null model. This
is a decision problem, and classical statistics is not appropriate
here, nor is it in scientific inference.
--
This address is for information only. I do not claim that these views
are those of the Statistics Department or of Purdue University.
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399
[EMAIL PROTECTED] Phone: (765)494-6054 FAX: (765)494-0558
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