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View Full Version : Re: Stats Power. Report Confidence Limits - p values



Niko Troje
01-26-2005, 04:29 AM
You are confusing something here. You dentist's 80% success rate (or the
20% failure rate) has got nothing to do with your type I error
probabilty. The alpha value reported in a statistical test would be the
probablity that in 80% of the cases your dentist's patients would get
better anyway, that is, assuming the null hypothesis that your dentist's
treatment has no effect.

So don't worry. You probably have a very good dentist.

Niko

Bruce Etnyre, Ph.D., P.T. wrote:

> Would anyone like to comment on clinical significance?
>
> For example, my dentist can completely cure temporomandibular joint
> dysfunction (TMJ) in 80% of patients by applying a plastic splint to
> the teeth. Scientifically, this is not statistically significant. It
> does not even approach statistical significance. So statistically we
> would accept the null hypothesis that there is no difference in the
> treatment of TMJ by using this device or not because the level of
> confidence is only 80%.
>
> Statistically, my dentist is a failure, but clinically, a world-beater!
>
> BE
>
> At 9:58 AM -0500 1/26/05, Dr. Chris Kirtley wrote:
>
>> This brings up an interesting issue. I spoke to a statistician last
>> year who
>> told me that the only reason Fischer came up with these tables, and
>> indeed the
>> whole concept of significance testing, was because there were no
>> computers
>> available at that time. He considered T-tests, ANOVAs etc. to be stopgap
>> methods that could to be used to get an approximate estimate until
>> better
>> computing power came along (as he expected it would).
>>
>> If Fischer were to be alive today, he would likely be appalled that
>> we are
>> still using his extremely simplified methods. Apparently any decent real
>> statistician worth his salt these days performs a simulation in order to
>> compute the likelihood of error. I was never able to find out how
>> this is done,
>> but perhaps someone else on the list can enlighten us? It really is
>> time all of
>> us in biomechanics moved into the modern age!
>>
>> Bryan Kirking wrote:
>>
>>> To comment and question some of Dr. Allison's insight:
>>>
>>> >>My understanding of the arbitrary "line in the sand" of 0.05 was
>>> >>originally due to the choice of the original tables (pre computer)
>>
>>
>> --
>> Dr. Chris Kirtley MD PhD
>> Associate Professor
>> Dept. of Biomedical Engineering
>> Catholic University of America
>> Washington DC 20064
>> Alternative email: kirtleymd@yahoo.com
>>
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>
>
>
> --
> Bruce Etnyre, Ph.D., P.T.
> Kinesiology Department
> Professor and Chair
> Rice University
> 6100 Main MS 545
> Houston, Texas 77005
> USA
> etnyre@rice.edu
> Phone: (713)348-5936 or 8816
> FAX:(713)348-8808
>
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>
>

--
-----------------------------------------

Prof. Dr. Nikolaus Troje
Canada Research Chair
in Vision and Behavioural Sciences
Department of Psychology
Queen's University
Kingston, Ontario, K7L 3N6, CANADA

phone: 613 533-6017
fax: 613 533-2499
email: troje@post.queensu.ca
www: http://www.bml.psyc.queensu.ca

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