search for: questionkey

I've got a table of 1 row per observation. 16 questions * n subjects * 4 classrooms (2 teachers * 2 conditions) I'd like to run some simple regressions that look something like this: lm(length ~ elapsed) I'd like to do the regressions several times, split out by questionkey, student, class. What I've been doing is using a series of which's to create new data sets (e.g. class1, class2, class3, class4) and running the regressions (or whatever) against each of those new data sets. It seems that there should be better a way to do this. -- Jay Pfaffman...