I agree that it's the detail about which we disagree! However, one
detail is pretty important - I still think you are confusing the trial
and the statistical test. The same confusion is shown on the web site.
I agree totally that if the treatment appears to be significantly worse
than the control treatment (as in your last paragraph below, and as you
illustrate with an example on the web page) you have to do something
about it. But - this 'something' is quite different from the 'something'
you do if you conclude that the treatment is significantly better than
the control.
In essence, you are setting up a second question - that is, a second
pair of hypotheses. The primary question is: Is the new treatment better
than the control? (This has to be the primary question in most such
research - it would certainly be unethical to trial a treatment that you
think is worse than the control.) The secondary question is: Is the new
treatment worse than the control?
Actually the secondary question is: If the new treatment is no better,
is it worse than the control?
I concede that you can view these two questions as one, but I think that
that is confusing and (therefore) not good design.
Regards,
Alan
Jerry Dallal wrote:
>
> We don't really disagree. Any apparent disagreement is probably due
> to the abbreviated kind of discussion that takes place in Usenet.
> See http://www.tufts.edu/~gdallal/onesided.htm
>
> Alan McLean ([EMAIL PROTECTED]) wrote:
>
> > My point however is still true - that the person who receives
> > the control treatment is presumably getting an inferior treatment. You
> > certainly don't test a new treatment if you think it is worse than
> > nothing, or worse than current treatments!
>
> Equipoise demands the investigator be uncertain of the direction.
> The problem with one-tailed tests is that they imply the irrelevance
> of differences in a particular direction. I've yet to meet the
> researcher who is willing to say they are irrelevant regardless of
> what they might be.
>
> > For the sample data I compute xbar (the difference of sample means if
> > there is a control group). There are three possibilities.
> >
> > 1. xbar is negative
>
> > If 1 does happen, we would conclude either that the new treatment is no
> > better than the control, and may be worse. In either case we junk the
> > new treatment.
>
> The question is, do you look to see how much worse? If the answer
> is no, then I've no argument. But everyone looks. It's unethical not
> to!
>
> --Jerry
>
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--
Alan McLean ([EMAIL PROTECTED])
Department of Econometrics and Business Statistics
Monash University, Caulfield Campus, Melbourne
Tel: +61 03 9903 2102 Fax: +61 03 9903 2007
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