In a rather simple regression, I’d like to ask the question, for high trees, whether it makes a difference (for volume) whether a three is thick.
If my interpretation is correct, for low trees, i.e. for which trees$isHigh == FALSE, the answer is yes. The problem is how to "merge" the standard errors. Code follows. data(trees) trees$isHigh <- trees$Height > 76 trees$isThick <- trees$Girth > 13 m <- lm(trees$Volume ~ trees$isHigh + trees$isThick + trees$isHigh:trees$isThick) summary(m) I might be mistaken, but a workaround is to rewrite the model as follows, which shows that the answer is yes. However, I would very much like to know how to answer the question with the original model. data(trees) trees$isLow <- trees$Height <= 76 trees$isThick <- trees$Girth > 13 m <- lm(trees$Volume ~ trees$isLow + trees$isThick + trees$isLow:trees$isThick) summary(m) -- View this message in context: http://r.789695.n4.nabble.com/Standard-errors-in-regression-models-with-interactions-terms-tp4680104.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.
