Help with three-way anova
On Wed, 2005-04-06 at 09:11 +0100, michael watson (IAH-C) wrote:
OK, so I tried using lm() instead of aov() and they give similar results: My.aov <- aov(IL.4 ~ Infected + Vaccinated + Lesions, data) My.lm <- lm(IL.4 ~ Infected + Vaccinated + Lesions, data)
Incidentally, if you want interaction terms you need lm(IL.4 ~ Infected * Vaccinated * Lesions, data) for all the possible interactions in the model (BUT you need enough degrees of freedom from the start to be able to do this).
If I do summary(My.lm) and summary(My.aov), I get similar results, but not identical. If I do anova(My.aov) and anova(My.lm) I get identical results. I guess that's to be expected though. Regarding the results of summary(My.lm), basically Intercept, Infected and Vaccinated are all significant at p<=0.05. I presume the signifcance of the Intercept is that it is significantly different to zero? How do I interpret that?
I guess it's all due to the contrast matrix you used. Check with contrasts() the term(s) in the datafile you use as independent variables, and change the contrast matrix as you see fit. HTH, F
Federico C. F. Calboli Department of Epidemiology and Public Health Imperial College, St Mary's Campus Norfolk Place, London W2 1PG Tel +44 (0)20 7594 1602 Fax (+44) 020 7594 3193 f.calboli [.a.t] imperial.ac.uk f.calboli [.a.t] gmail.com