Dear Dr. Bates, Thank you very much for your response. --- Douglas Bates <[EMAIL PROTECTED]> escribió:
> 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 had consulted the algorithm described in Pinheiro and Bates. > > 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". However, what I don't understand (among other things) is why my two parameters appear to be estimated at different grouping levels (based on the DF values). Affect this different values of DF at the estimates parameters? The estimates fixed effects were get at the same level of grouping? > > 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. > I apreciate any response. > > --------------------------------- > > 1GB gratis, Antivirus y Antispam > > Correo Yahoo!, el mejor correo web del mundo > > Abrí tu cuenta aquí > > [[alternative HTML version deleted]] > > > > > > > > ______________________________________________ > > R-help@stat.math.ethz.ch mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html > > > > > 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 __________________________________________________ Correo Yahoo! Espacio para todos tus mensajes, antivirus y antispam ¡gratis! ¡Abrí tu cuenta ya! - http://correo.yahoo.com.ar ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
