Hi I am not at all an expert in step. From the help page I inferred that
step(lm1, scope=list(lower=~Catholic)) keeps Catholic in model. So something like step(RegModel, direction ="backward",scope=list(lower=~sex+height)) shall leave those two in a model. AFAIK there is no parameter alpha in a step function. Regards Petr > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Einat > Sent: Wednesday, November 21, 2012 1:41 PM > To: r-help@r-project.org > Subject: Re: [R] Stepwise analysis with fixed variables > > These are my questions: > > 1. For example, if this is my code: > > >RegModel = > lm(glucose~sex+BMI+height+weight+education+ses,weight=w_without_non_res > ponse) > >summary(RegModel) > >step(RegModel, direction ="backward",scope=list(lower=?,upper=?)) > > and I want the sex and height variables to be fixed, but the rest of > the variables to go into the backward analysis, how should I write the > scope function? > > 2.How can I add an alpha level to the step function as a criterion for > the backward regression analysis? > > Thank you :) > > > > -- > View this message in context: http://r.789695.n4.nabble.com/Stepwise- > analysis-with-fixed-variables-tp4650015p4650283.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. ______________________________________________ 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.
