I have heard conflicting opinions on Bonferroni. One person told me that I cannot use a Bonferroni comparison without a significant interaction. Does that also mean that you don't need a significant overall effect for a Bonferroni post-hoc? Another person told me that Bonferroni correction eliminates the need for a significant interaction. Rats are tested for their ability to recognize an object (familiar or unfamiliar) and receive a drug or vehicle treatment, so I have a 2x2 ANOVA. The unfamilar condition is basically a control condition to account for changes in general activity. I have a significant effect of recognition, and a significant effect of drug treatment, but no significant interaction. I did some Bonferroni post-hoc tests to sort out the effect I am really interest in: Vehicle familiar vs drug familiar is significant vehicle unfamiliar vs drug unfamiliar is not.
This is exactly what we expected, but I'm just not sure of legitimacy statistically speaking as far as the post-hocs go. I am likely missing something here, but I am a bit confused by some of the comments.
Planning to do a generic analysis from the beginning (or to look at the omnibus F test to see if some factor was signficant) is not enough to justify planned contrast.
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