"Robert J. MacG. Dawson" wrote:
> > > But I don't see why either the advertiser or the consumer advocate
> > would, or should, do a two-tailed test.
>
> The idea is that the "product" of these tests is a p-value to be used
> in support of an argument. The evidence for the proposal is not made any
> stronger by the tester's wish for a certain outcome; so the tester
> should not artificially halve the reported p-value.
>
> Superficially, the idea of halving your p-values, doubling your chance
> of reporting a "statistically significant" result in your favored
> direction if there is really nothing there, and as a bonus, doing a
> David-and-Uriah job ("And he wrote in the letter, saying, Set ye Uriah
> in the forefront of the hottest battle, and retire ye from him, that he
> may be smitten, and die.") on any possible finding in the other
> direction, may seem attractive. A moment's thought should persuade us
> that it is not ethical.
>
> -Robert Dawson
I'm not sure I understand the argument, but it may be irrelevant
regardless. Most consumer protection laws are written to punish the
"instance" and have nothing to do with "statistics" in general or
means in particular. This protects you from my friend the shopkeeper
who puts 1 lb in your 5 lb bag of sugar and 9.1 lbs in mine.
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