`.' means `what is already there'. In your case, .^2 is 1^2 which is 1, so it behaves correctly.
Only in a *fit* involving a *data* argument does `.' mean `the rest of the variables'. On Mon, 4 Oct 2004, Yu Shao wrote: > Hello: > > I am doing forward stepwise analysis on the glm model. I am trying to use model > operator in the "upper" scope formula, for example, > > scope=list(lower=~1,upper=~ .^2) > > but the upper bound of the scope seems to be ignored and add1 is not performed > at all, while if the terms are explicitly listed in the formula, the step > function seems to work properly. Example: > > > version > platform sparc-sun-solaris2.9 > arch sparc > os solaris2.9 > system sparc, solaris2.9 > status > major 1 > minor 9.0 > year 2004 > month 04 > day 12 > language R > > > testdata > effect fa1 fa2 fa3 > 1 0.5054526 -1.4 1 -15.42 > 2 0.1366526 -2.5 3 -14.72 > 3 0.4798526 -1.1 3 -16.43 > 4 0.5566526 -4.6 2 -17.62 > 5 0.6568526 -3.5 7 -5.41 > 6 0.6653526 0.0 5 -11.88 > 7 0.6376526 0.0 5 -11.72 > 8 0.5203526 -2.9 -1 -14.72 > 9 0.4905526 -2.1 2 -17.68 > 10 0.6376526 -1.1 1 -13.39 > > > step (glm(effect ~ 1 , data=testdata), scope=list(lower=~1,upper=~.), > direction='forward') > Start: AIC= -5.89 > effect ~ 1 > > > Call: glm(formula = effect ~ 1, data = testdata) > > Coefficients: > (Intercept) > 0.5287 > > Degrees of Freedom: 9 Total (i.e. Null); 9 Residual > Null Deviance: 0.2178 > Residual Deviance: 0.2178 AIC: -5.89 > > ================================================================ > > But if I listed the term explicitly in the formula, then step function seemed to > work correctly: > > > step (glm(effect ~ 1 , data=testdata), > scope=list(lower=~1,upper=~fa1+fa2+fa3), direction='forward') > Start: AIC= -5.89 > effect ~ 1 > > Df Deviance AIC > + fa3 1 0.1778 -5.9188 > <none> 0.2178 -5.8901 > + fa2 1 0.2023 -4.6271 > + fa1 1 0.2065 -4.4194 > > Step: AIC= -5.92 > effect ~ fa3 > > Df Deviance AIC > <none> 0.1778 -5.9188 > + fa1 1 0.1698 -4.3783 > + fa2 1 0.1770 -3.9605 > > Call: glm(formula = effect ~ fa3, data = testdata) > > Coefficients: > (Intercept) fa3 > 0.78310 0.01830 > > Degrees of Freedom: 9 Total (i.e. Null); 8 Residual > Null Deviance: 0.2178 > Residual Deviance: 0.1778 AIC: -5.919 > ================================================================ > > I've lookup the online manual of step function but couldn't find a solution. > Thanks in advance, > > Yu Shao > Wadsworth Center, New York State Department of Health, > Albany, NY 12208 > > ______________________________________________ > [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 > > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [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