A. G. McDowell <[EMAIL PROTECTED]> wrote in
sci.stat.edu:
>The significance value associated with the one-tailed test will always
>be half the significance value associated with the two-tailed test,
For means, yes. Not for proportions, I think. (I wasn't asking about
a proportion in my original query.)
>If the true state of affairs is
>that the true difference is (e.g.) 13.0, then you are correct if you
>declare that the difference is > 0, and we are implicitly ignoring
>errors you make by declaring that the difference is 0. You can only make
>an error by declaring that the difference is < 0. But when the true
>situation is that the difference is zero you are also making an error if
>you say that the difference is < 0. In fact, it is easier to make the
>error in this situation, because you are more likely to see a -ve
>statistic when the true value is 0 than when the true value is 13. So
>the error rate from jumping the wrong way when there is a true
>difference is less than the error rate from jumping any way when there
>is no true difference, and you are justified in stating the direction of
>the distance.
I really like this way of explaining it; thanks.
--
Stan Brown, Oak Road Systems, Cortland County, New York, USA
http://oakroadsystems.com/
"Don't move, or I'll fill you full of [... pause ...] little
yellow bolts of light." -- Farscape, first episode
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