Hi
James M. Clark Professor of Psychology 204-786-9757 204-774-4134 Fax [email protected] Department of Psychology University of Winnipeg Winnipeg, Manitoba R3B 2E9 CANADA >>> "Wuensch, Karl L" <[email protected]> 11-Jan-09 10:57 AM >>> First, a trivial point. The F test employed in traditional ANOVA is a one-tailed test -- regardless of the ordering of the differences among the group means, greater differences lead to a larger F. Accordingly, it is a one-tailed, upper-tailed, test. It could be done as a lower-tailed test if you put the error term in the numerator, as is done with some multivariate test statistics. JC: I assumed that we were using one-tailed as a standard way of referring to directional alternative hypotheses. Certainly that is how I used it. In that sense, standard F test is non-directional (i.e., also generally somewhat misnamed, as Karl notes, as two-tailed tests). It is non-directional, because the F is insensitive to the direction of differences among the means and when k = 2 the upper tail of F contains both the lower and upper tails of t (hence t^2 = F for both observed and critical values, using a nondirectional, two-tailed alternative for t). Take care Jim --- To make changes to your subscription contact: Bill Southerly ([email protected])
