The models are NOT equivalent. Why would you’ll think they were? — David
Sent from my iPhone > On Feb 9, 2022, at 11:10 PM, Bromaghin, Jeffrey F via R-help > <r-help@r-project.org> wrote: > > Hello, > > I was constructing a simple linear model with one categorical (3-levels) and > one quantitative predictor variable for a colleague. I estimated model > parameters with and without an intercept, sometimes called reference cell > coding and cell means coding. > > Model 1: yResp ~ -1 + xCat + xCont > Model 2: yResp ~ xCat + xCont > > These models are equivalent and the estimated coefficients come out fine, but > the R-squared and F statistics returned by summary() differ markedly. I spent > some time looking at the code for both lm() and summary.lm() but did not find > the source of the difference. aov() and anova() results also differ, so I > suspect the issue involves how the sums of squares are being computed. I've > also spent some time trying to search online for information on this, without > success. I haven't used lm() for quite a while, but my memory is that these > differences didn't occur in the distant past when I was teaching. > > Thanks in advance for any insights you might have, > Jeff > > Jeffrey F. Bromaghin > Research Statistician > USGS Alaska Science Center > 907-786-7086 > Jeffrey Bromaghin, Ph.D. | U.S. Geological Survey > (usgs.gov)<https://www.usgs.gov/staff-profiles/jeffrey-bromaghin> > Ecosystems Analytics | U.S. Geological Survey > (usgs.gov)<https://www.usgs.gov/centers/alaska-science-center/science/ecosystems-analytics> > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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 -- To UNSUBSCRIBE and more, see 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.
