On Mar 6, 2013, at 4:46 AM, Kjetil Kjernsmo <kje...@ifi.uio.no> wrote:
> All, > > I have just returned to R after a decade of absence, and it is good to see > that R has become such a great success! I'm trying to bring Design of > Experiments into some aspects of software performance evaluation, and to > teach myself that, I picked up "Experiments: Planning, Analysis and > Optimization" by Wu and Hamada. I try to reproduce an analysis in the book > using lm, but have to conclude I don't understand what lm does in this > context, even though I end up at the desired result. I'm currently using R > 2.15.2 on a recent Fedora system, but I get the same result on Debian Wheezy > and Debian Squeeze. I think the discussion below can be followed without > having the book at hand though. > > I'm working with tables 5.2 and 5.5 in the above mentioned book. Table 5.2 > contains data from the "Leaf spring experiment". The dataset is also in this > zip file: > > ftp://ftp.wiley.com/public/sci_tech_med/experiments-planning/data%20sets.zip > > I've learned from the book that the effects can be found using a linear model > and double the coefficients. So, I do > > leaf <- > > read.table("/ifi/bifrost/a03/kjekje/fag/experimental-planning/book-datasets/LeafSpring > > table 5.2.dat", col.names=c("B", "C", "D", "E", "Q", paste("r", 1:3, > > sep=""), "yavg", "ssq", "lnssq")) > > leaf.lm <- lm(yavg ~ B * C * D * E * Q, data=leaf) > > leaf.lm > I'll ignore the rest of your question, in the hope that this will answer them sufficiently. You probably want a simple linear model, specified in R using "+" instead of "*". > leaf.lm <- lm(yavg ~ B + C + D + E + Q, data=leaf) > leaf.lm Call: lm(formula = yavg ~ B + C + D + E + Q, data = leaf) Coefficients: (Intercept) B+ C+ D+ E+ Q+ 7.50084 0.22125 0.17625 0.02875 0.10375 -0.25960 Does this give you the numbers you expect? Peter > > > Kjetil > -- > Kjetil Kjernsmo > PhD Research Fellow, University of Oslo, Norway > Semantic Web / SPARQL Query Federation > kje...@ifi.uio.no http://www.kjetil.kjernsmo.net/ > > ______________________________________________ > 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. ______________________________________________ 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.
