On 1/27/06, gabriela escati peñaloza <[EMAIL PROTECTED]> wrote: > Hi, I' m having a hard time understanding the computation of degrees of > freedom
So do I and I'm one of the authors of the package :-) > when runing nlme() on the following model: > > > formula(my data.gd) > dLt ~ Lt | ID > > TasavB<- function(Lt, Linf, K) (K*(Linf-Lt)) > > my model.nlme <- nlme (dLt ~ TasavB(Lt, Linf, K), > data = my data.gd, > fixed = list(Linf ~ 1, K ~ 1), > start = list(fixed = c(70, 0.4)), > na.action= na.include, naPattern = ~!is.na(dLt)) > > > summary(my model.nlme) > Nonlinear mixed-effects model fit by maximum likelihood > Model: dLt ~ TasavB(Lt, Linf, K) > Data: my data.gd > AIC BIC logLik > 13015.63 13051.57 -6501.814 > Random effects: > Formula: list(Linf ~ 1 , K ~ 1 ) > Level: ID > Structure: General positive-definite > StdDev Corr > Linf 7.3625291 Linf > K 0.0845886 -0.656 > Residual 1.6967358 > Fixed effects: list(Linf + K ~ 1) > Value Std.Error DF t-value p-value > Linf 69.32748 0.4187314 402 165.5655 <.0001 > K 0.31424 0.0047690 2549 65.8917 <.0001 > Standardized Within-Group Residuals: > Min Q1 Med Q3 Max > -3.98674 -0.5338083 -0.02783649 0.5261591 4.750609 > Number of Observations: 2952 > Number of Groups: 403 > > > > Why are the DF of Linf and K different? I would apreciate if you could > point me to a reference The algorithm is described in Pinheiro and Bates (2000) "Mixed-effects Models in S and S-PLUS" published by Springer. See section 2.4.2 I would point out that there is effectively no difference between a t-distribution with 402 df and a t-distribution with 2549 df so the actual number of degrees of freedom is irrelevant in this case. All you need to know is that it is "large". I will defer to any of the "degrees of freedom police" who post to this list to give you an explanation of why there should be different degrees of freedom. I have been studying mixed-effects models for nearly 15 years and I still don't understand. > Note: I working with Splus 6.1. for Windows Technically this email list is for questions about R. There is another list, [EMAIL PROTECTED], for questions about S-PLUS. > > > Lic. Gabriela Escati Peñaloza > Biología y Manejo de Recursos Acuáticos > Centro Nacional Patagónico(CENPAT). > CONICET > Bvd. Brown s/nº. > (U9120ACV)Pto. Madryn > Chubut > Argentina > > Tel: 54-2965/451301/451024/451375/45401 (Int:277) > Fax: 54-29657451543 > > --------------------------------- > 1GB gratis, Antivirus y Antispam > Correo Yahoo!, el mejor correo web del mundo > Abrí tu cuenta aquí > [[alternative HTML version deleted]] > > > > ______________________________________________ > [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 > > ______________________________________________ [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
