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slawson74
01-26-2005, 06:06 AM
Dear Bryan,

I think the problem below lies in your assumption that
the null hypothesis is untrue merely because you have
rejected it.
"one rejects the null hypothesis, making the null
untrue(?)"

As everyone else so rightly said, there is still a
chance that it is true and that you have therefore
made a type I error. That chance is alpha.

The fashion seems increasingly to be to do away with
cut offs and quote the specific confidence level for
you results. This is probably wise under the
circumstances but I think Chris Kirtley is right,
maybe it's high time we started considering some more
modern options. I look forward to hearing from someone
who can tell us how to do the simulations. Perhaps we
could even consider a workshop at the next appropriate
conference?

Sian Jenkins Lawson



--- Bryan Kirking wrote:

> If "alpha, or type I error" is defined (as best as I
> know) as the
> probability of rejecting the null hypothesis when
> the null hypothesis is true,
> And based on the associated p-value or confidence
> interval, one rejects the
> null hypothesis, making the null untrue(?)
>
> Then doesn't alpha, or type I error become an
> impossibility (i.e, reject a
> true null when the p-value suggests the null is not
> true). I suspect the
> answer comes down to Dr. Greiner's remark that this
> is only one experiment,
> but if we replicate the experiment 100 times
> wouldn't the same situation be
> present? Does type II error (probability of not
> rejecting a false null)
> now become the best measure of confidence (and I use
> confidence for lack of
> a better term)?
>
> As to predefining the alpha level, the issue becomes
> even more difficult to
> me when I consider that most studies I read or
> perform usually have
> multiple comparisons. If one doesn't set overall
> confidence levels and
> therefore individual levels a priori, how do we
> guarantee that the overall
> confidence is maintained? Do we do analyses that
> "accepts" = 0.026 given
> that another variable is p=0.024 and therefore
> maintains 0.05? To me, this
> is a very good reason for keeping with predefined
> values, as long as those
> values are suitable for your application.
>
>
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