[R] Contrast SS

From: Ista Zahn <izahn_at_psych.rochester.edu>
Date: Fri, 28 Nov 2008 11:24:02 -0500


Hi all,
Hopefully this is an easy question and I've overlooked something simple. I want to present specific contrasts in an ANOVA table. I can of course get the significance tests with summary.lm, but my adviser wants the results in ANOVA format. Here is a minimal example:

> x <- factor(c(rep("condition.1", 5), rep("condition.2", 5), rep("condition.3", 5)))
> y <- rnorm(15)

I know there are all kinds of built-in contrasts, but I specifically want to contrast groups 1 and two with group 3, and I'm more comfortable setting them by hand:

> contrasts(x) <- matrix(c(-1,-1,2, -1,1,0), 3,2)
> m.1 <- lm(y ~ x)

I can test the contrasts with

> summary(m.1)

but the results are not formatted in an ANOVA table. I can format the results in an ANOVA table

> anova(m.1)

but this doesn't give me results for the contrast.

Any help is greatly appreciated.

-Ista



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