simulating the anova
On Mar 5, 2008, at 12:03 AM, Will Holcomb wrote:
I have been trying to figure out how to run a simple simulation of the ANOVA and I'm coming up just a bit short. The code I've got is: cohen.f = .25 groups = 4 between.var = 19 within.var = between.var / cohen.f ^ 2 n = 500 sim.means = rnorm(n = groups, mean = 0, sd = sqrt(between.var)) sim.data = lapply(sim.means, function(mean) rnorm(n = n, mean = mean, sd = sqrt(within.var))) sim.anova = ? I'm pretty sure I've got data with the between group and within group variances that I want. I don't really know how to run an ANOVA on it though. All the examples I've been able to find (with aov and anova) require an explicit model. The ANOVA just tests the equivalence of means for a set of groups, right? Can I not just tell it to give me the likelihood the means are equal for all the columns without writing an explicit model.
I don't know if you can without writing an explicit model or not, but writing the model isn't that hard: simdata2 <- do.call(data.frame, sim.data) names(simdata2) <- LETTERS[1:4] simdata3 <- stack(simdata2) fit <- lm(values~ind, data=simdata3) summary(fit) anova(fit) Unless I misunderstood what you wanted to do.
Any help would be appreciated, Will
Haris Skiadas Department of Mathematics and Computer Science Hanover College