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Topic: small confidence limit to demonstrate inability to reject H0?
Replies: 4   Last Post: Oct 13, 2013 4:09 PM

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Richard Ulrich

Posts: 2,961
Registered: 12/13/04
Re: small confidence limit to demonstrate inability to reject H0?
Posted: Oct 11, 2013 6:48 PM
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On Fri, 11 Oct 2013 07:29:35 -0700 (PDT),

>On Thursday, October 10, 2013 7:08:03 PM UTC-4, Rich Ulrich wrote:
> <...some confirmations that small p-values do not demonstrate a
> lack difference, and that the use of large p-values may be due to
> historical lack of understanding, which may be improving...>

>> As a very general rule, p-levels are not good indicators of effect
>> size. Or, conversely, for lack-of-effect size. N is the huge
>> confounder, plus, it depends on how sensitive your test is for
>> finding an "effect."

>Understood. I'm just focusing on acceptance/rejection of H0.

>> When you want to show similarity, you want to show a narrow CI on
>> some relevant difference, for some meaningful measure... not merely
>> an absence of "demonstrated" difference. Crappy measures can give
>> you apparent similarities.

>My understanding is that narrow CI can only show lack of evidence against H0, but can never show the evidence for H0.

As Herman says in a post that *seems* to reply to this
(although he tacked on to your other comment from about
the same time), it is an easy conventional comment that
"The null hypothesis is never true."

A narrow CI on the size of a difference gives us evidence
that the difference is not larger. Or, not large enough
to matter.

And I don't worry about the Bayeisian approach.

Rich Ulrich

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