I was using Version 2.3.1 for Windows (binary download version). Guess I should be using the latest version, (but the reason is I'm writing up my PhD and I thought my results would be more 'repeatable' if I didn't keep changing my version of the software, I didn't really think there would be any glitches as big as this). Sorry if this is a waste of your time. And thanks very much for replying so quickly.
Jenny _____________ Jenny Hodgson Department of Biology - area 18 PO box 373 University of York YO10 5YW UK Tel: 01904 328623 Peter Dalgaard wrote: > Jenny Hodgson wrote: > >> Dear R Help, >> I have noticed some inconsistent behaviour of add1 and drop1 with a >> weighted linear model, which affects the interpretation of the results. >> I have these data to fit with a linear model, I want to weight them >> by the relative size of the geographical areas they represent. >> _________________________________________________________________________________________ >> >> >> > example >> y x1 x2 weights >> 1 -4.546477 0.1859556 50.00000 0.9466022 >> 2 1.484246 0.4740497 29.88000 1.3252430 >> 3 2.203681 0.8594264 16.93333 0.9466022 >> 4 1.943163 0.8713360 42.11765 2.7766997 >> 5 1.886473 0.9006082 19.00000 0.9466022 >> 6 1.795393 0.8455183 23.68421 1.1674760 >> 7 1.878077 0.5641396 35.00000 0.8203885 >> 8 -4.215484 0.4356858 58.75000 0.4417477 >> 9 1.993339 0.5440061 19.28571 0.8519420 >> 10 1.560869 0.6285066 19.54545 0.8203885 >> 11 2.761535 0.7017720 15.83333 0.1262136 >> 12 0.995959 0.4638751 0.00000 0.9466022 >> 13 -4.516514 0.2794199 77.85714 0.8834954 >> > sum(example$weights) >> [1] 13.00000 >> >> > model<-lm(y~1,data=example,weights=weights) >> > add1(model,.~.+x1+x2) >> Single term additions >> >> Model: >> y ~ 1 >> Df Sum of Sq RSS AIC >> <none> 94.000 27.719 >> x1 1 55.290 38.710 18.185 >> x2 1 58.630 35.371 17.012 >> > > Which version of R??! > > I get (2.4.1 on Fedora 6): > > > add1(model,.~.+x1+x2) > Single term additions > > Model: > y ~ 1 > Df Sum of Sq RSS AIC > <none> 74.541 24.703 > x1 1 44.377 30.164 14.942 > x2 1 36.619 37.922 17.918 > ______________________________________________ [email protected] 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.
