Will Hopkins wrote:
>
> Jerry Dallal wrote, ironically:
> >If you're doing a 1 tailed test, why test at all? Just switch from
> >standard treatment to the new one. Can't do any harm. Every field
> >is littered with examples where one-tailed tests would have led to
> >disasters (harmful treatments missed, etc.) had they been used.
>
> As you well know, Jerry, 5% is arbitrary.
>
It wasn't ironically and has nothing to do with 5%. As Marvin Zelen
has pointed out, one-tailed tests are unethical from a human
subjects perspective because they state that the difference can go
in only one direction (we can argue about tests that are similar on
the boundary, but I'm talking about how they are used in practice).
If the investigator is *certain* that the result can go in only one
direction, then s/he is ethically bound not to give a subject a
treatment that is inferior to another.
Consider yourself or someone near and dear with a fatal condition.
You go to a doc who says, "I can give you A with P(cure) in your
case of 20% or I can give you B for which P(cure) can't be less than
20% and might be higher. In fact, I wouldn't even consider B if
there weren't strong reasons to suspect it might be higher. And
let's not forget it can't be lower than 20%. I just flipped a
coin. YOU CAN'T HAVE "B"!"
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