Re: p-value of one-tailed test

[Lise DeShea]

Most software packages set the default to a two-tailed test on t-tests.  For example, if df = 23 and t = 2.5, then p would be reported as .02.  That means .01 is being cut off by t=2.5 and .01 is being cut off by t= -2.5.  You only care about half the reported p.  So you would say p=.01.  BUT you must retain the null hypothesis if you predicted the wrong direction, and it's a moot point what p is.

At 11:25 AM 4/4/01 -0500, you wrote:

Hi,
What is the p-value of a t-statistic significant (significant level shown by
the software is p) in the wrong direction in an one-tailed test? Should we
modified it to (1-p)? Or it is just p?


Erik




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