Hello, I have two questions regarding multiple comparison tests for a one-way ANOVA (fixed effects model).
1) Consider the "Protected LSD test," where we first use the F statistic to test the hypothesis of equality of factor level means. Here we have a type I error rate of alpha. If the global F test is significant, we then perform a series of t-tests (pairwise comparisons of factor level means), each at a type I error rate of alpha. This may seem like a stupid question, but how does this test preserve a type I error for the entire experiment? I understand that with a Bonferroni-type procedure, we can test each pairwise comparison at a certain rate, so that the overall type I error rate of the experiment will be at most a certain level. But with the Protected LSD test, I don't quite see how the comparisons are being protected. Could someone please explain to me the logic behind the LSD test? 2) Secondly, are contrasts used primarily as planned comparisons? If so, why? I would very much appreciate it if someone could take the time to explain this to me. Many thanks. Go Get It! Send FREE Valentine eCards with Lycos Greetings http://greetings.lycos.com ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at http://jse.stat.ncsu.edu/ =================================================================
