Thanks! Now it is clear. Francisco
On Wed, 16 May 2012 07:32:56 -0400, Gabor Grothendieck wrote > On Tue, May 15, 2012 at 11:20 PM, Gabor Grothendieck > <ggrothendi...@gmail.com> wrote: > > On Tue, May 15, 2012 at 8:08 PM, Francisco Mora Ardila > > <fm...@oikos.unam.mx> wrote: > >> Hi all > >> > >> I have fitted a model usinf nls function to these data: > >> > >>> x > >> [1] 1 0 0 4 3 5 12 10 12 100 100 100 > >> > >>> y > >> [1] 1.281055090 1.563609934 0.001570796 2.291579783 0.841891853 > >> [6] 6.553951324 14.243274230 14.519899320 15.066473610 21.728809880 > >> [11] 18.553054450 23.722637370 > >> > >> The model fitted is: > >> > >> modellogis<-nls(y~SSlogis(x,a,b,c)) > >> > >> It runs OK. Then I calculate confidence intervals for the actual data > >> using: > >> > >> dataci<-predict(as.lm(modellogis), interval = "confidence") > >> > >> BUt I don´t get smooth curves when plotting it, so I want to get other > >> "confidence > >> vectors" based on a new x vector by defining a new data to do predictions: > >> > >> x0 <- seq(0,15,1) > >> dataci<-predict(as.lm(modellogis), newdata=data.frame(x=x0), interval = "confidence") > >> > >> BUt it does not work: I get the same initial confidence interval > >> > >> Any ideas on how to get tconfidence and prediction intervals using new X > >> data on a > >> previous model? > >> > > > > as.lm is a linear model between the response variable and the gradient > > of the nonlinear model and as we see below x is not part of that > > linear model so x can't be in newdata when predicting from the tangent > > model. We can only make predictions at the original x points. For > > other x's we could use Interpolation. See ?approx (?spline can also > > work in smooth cases but in the example provided the function has a > > kink and that won't work well with splines.) > > > >> as.lm(modellogis)$model > > y a b c (offset) > > 1 1.281055090 0.06601796 -4.411829e-01 1.168928e+00 1.397153 > > 2 1.563609934 0.04798815 -3.268846e-01 9.766080e-01 1.015584 > > 3 0.001570796 0.04798815 -3.268846e-01 9.766080e-01 1.015584 > > 4 2.291579783 0.16311227 -9.767241e-01 1.597189e+00 3.451981 > > 5 0.841891853 0.12203013 -7.665928e-01 1.512752e+00 2.582551 > > 6 6.553951324 0.21464369 -1.206154e+00 1.564573e+00 4.542552 > > 7 14.243274230 0.74450055 -1.361047e+00 -1.455630e+00 15.756031 > > 8 14.519899320 0.59707858 -1.721353e+00 -6.770205e-01 12.636107 > > 9 15.066473610 0.74450055 -1.361047e+00 -1.455630e+00 15.756031 > > 10 21.728809880 1.00000000 -2.943955e-13 -9.073765e-12 21.163223 > > 11 18.553054450 1.00000000 -2.943955e-13 -9.073765e-12 21.163223 > > 12 23.722637370 1.00000000 -2.943955e-13 -9.073765e-12 21.163223 > > > > I have added a FAQ to the home page since this isn't the first time > this question has come up: > > http://nls2.googlecode.com#FAQs > > -- > Statistics & Software Consulting > GKX Group, GKX Associates Inc. > tel: 1-877-GKX-GROUP > email: ggrothendieck at gmail.com ---------------------- Francisco Mora Ardila Estudiante de Doctorado Centro de Investigaciones en Ecosistemas Universidad Nacional Autónoma de México ______________________________________________ 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.