On Mon, 8 Dec 2003 14:28:25 +0800, "Erica So" <[EMAIL PROTECTED]> wrote:
> After conducting the two way anova with REPEATED measure, I have > difficulties on understanding the Post hoc test. Could anyone suggest some > reference that I can refer to? Both website and reference book are ok. There are designed contrasts for oneway ANOVA which go by names like SNK and Tukey's. They have certain things in common: The contrasts are a subset of possible tests, and they may have rules for applying them, and they are based in theory on the shared within-group variance. Some people always insist that there should be an overall test that is 'significant' and so they call them "post hoc" tests. Two-way tests and in particular, repeated measures, don't have the shared variance that can safely, generally, be used. So, as it happens, there aren't any "post-hoc" tests that I know of, going by any of those names, that are widely recognized. I once read a really awkward description in one textbook, many, many pages for trying to apply a 'post-hoc' test, and that left me convinced that *that* test was not viable. I think I've heard that some stat-pack has something, but I don't know what and I surely would not trust it without reading its documentation and sources carefully. In biostatistical applications, followup tests for repeated measures are usually conducted as paired t-tests, using the variance term that relies on only the data being tested. They are not usually labeled as 'post-hoc' tests, though the logic is not too different if you merely apply the need for one overall test to justify the much-larger set of followups. Unequal correlations as well as unequal variances stand in the way of using the pooled tests of the oneway ANOVA, that go by those particular names as 'post-hocs'. You may want to read about "Bonferroni" correction; it can be used in various circumstances. So, what is it that brings to the surface the question of post-hocs for a repeated measure? suggested by a stat-pack, a reviewer, or convenient analogy? -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html "Taxes are the price we pay for civilization." . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
