The code below may not be the most optimized, but it should do the trick. I've implemented the permutation test, which by some nomenclatures is distinguished from the randomization test in that the latter is exhaustive while the former is not.
I'm eager to hear the views of the list on whether the permutation test fares when you use a parametric stat like the F as the focal statistic. I know that David Howell introduction to the test employs the F ( http://www.uvm.edu/~dhowell/StatPages/Resampling/Resampling.html). I personally think that in cases of known violation of normality and/or homogeneity of variance, it seems odd to incorporate MSerror into the focal statistic. I look forward to the list educating me if this view turns out to be uninformed. #make sure the factors are treated as such FactorA = factor(FactorA) FactorB = factor(FactorB) #get the observed Fs obs.aov = aov(Resp~FactorA*FactorB) obs.mainA.F = summary(obs.aov)[[1]]$F[1] obs.mainB.F = summary(obs.aov)[[1]]$F[2] obs.AbyB.F = summary(obs.aov)[[1]]$F[3] #prepare for the permutation loop perms = 1e4 perm.mainA.F = rep(NA,perms) perm.mainB.F = rep(NA,perms) perm.AbyB.F = rep(NA,perms) #run the permutation loop for(i in 1:perms){ Randomized.Resp = Resp[order(runif(length(Resp)))] perm.aov = aov(Randomized.Resp~FactorA*FactorB) perm.mainA.F[i] = summary(perm.aov)[[1]]$F[1] perm.mainB.F[i] = summary(perm.aov)[[1]]$F[2] perm.AbyB.F[i] = summary(perm.aov)[[1]]$F[3] } #compute the p-values p.mainA = mean(perm.mainA.F>obs.mainA.F) p.mainB = mean(perm.mainB.F>obs.mainB.F) p.AbyB = mean(perm.AbyB.F>obs.AbyB.F) #print the p-values print(p.mainA) print(p.mainB) print(p.AbyB) -- Mike Lawrence Graduate Student Department of Psychology Dalhousie University www.thatmike.com Looking to arrange a meeting? Do so at: http://www.timetomeet.info/with/mike/ ~ Certainty is folly... I think. ~ [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
