I've tried without success to calculate interaction and main effects contrasts using R. I've found the functions C(), contrasts(), se.contrasts() and fit.contrasts() in package gmodels. Given the url for a small dataset and the two-way anova model below, I'd like to reproduce the results from appended SAS code. Thanks. --Dale.
## the dataset (from Montgomery) twoway <- read.table("http://dsteele.veryspeedy.net/sta501/twoway.txt", col.names=c('material', 'temp','voltage'),colClasses=c('factor', 'factor', 'numeric')) ## the model fit <- aov(voltage ~ material*temp, data=twoway) /* SAS code */ proc glm data=twoway; class material temp; model voltage = material temp material*temp; contrast '21-22-31+32' material*temp 0 0 0 1 -1 0 -1 1 0; estimate '21-22-31+32' material*temp 0 0 0 1 -1 0 -1 1 0; contrast 'material1-material2' material 1 -1 0; estimate 'material1-material2' material 1 -1 0; contrast 'temp50 - temp80' temp 1 0 -1; estimate 'temp50 - temp80' temp 1 0 -1; run; ______________________________________________ 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.