Re: One or Two tails: II ?


Anon. wrote:
Kevin E. Thorpe wrote:
> Thom wrote:
>
>>> *** Marvin Zelen dismisses one-sided tests in another way--he
>>> finds them unethical! His
>>
>> argument is as simple as it is elegant. Put in terms of comparing a
>> new treatment to standard, anyone who insists on a one- tailed test
>> is saying the new treatment can't do worse than the standard. If
>> the new treament has any effect, it can only do better. The method
>> of analysis should be part of a study's design. If investigators
>> are prepared to justify the use of a one-tailed test at the start
>> of the study, then it is unethical not to give the new treatment to
>> everyone!
>>
>> I agree with Zelen's argument in that context, but there are other
>> limited contexts which make some directional tests sensible and
>> ethical. For example in a replication and extension one might
>> introduce a manipulation/intervention expected to influence effect
>> A but not effect B. If effect B is well established in the
>> literature one might use the more powerful one sided test to
>> establish that your participants demonstrated effect B. For effect
>> A one would use a two sided test.
>>
>> Thom
>
>
> One other situation where I feel you can reasonable justify a
> one-sided test is where you would only administer a treatment if it
> was superior. I'm thinking here of a surgical intervention compared
> to standard medical care. In order to justify exposing a patient to
> the risks associated with a surgery, it _better_ be superior to the
> medical care they would receive, especially when the surgery will be
> in addition to the standard medical care.
>
You'll know better, but I would guess that such a proceedure would have
gone through some screening (either formal trials, or assessment by
experts) to check if it was obviously worse, so the probability of it
being worse is small a priori. Does this match with what actually goes on?

Bob


Well, hopefully. But take a look at the EC/IC Bypass trial (which
I was not involved with and don't have the reference). EC/IC
was no better than medical and insurance companies stopped
funding the procedure. So, if you would not use a surgery if
it was just as good as non-surgical mangement, you could argue
that you don't care if it's actually worse.

--
Kevin E. Thorpe
Assistant Professor, Department of Public Health Sciences
Faculty of Medicine, University of Toronto

.

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