# Forum: help

Monitor Forum | Start New ThreadRE: nlssystemfit using SUR method [ reply ] By: Arne Henningsen on 2014-09-14 06:59 | [forum:41452] |

Dear Francisco I think that nlsystemfit() can estimate your model only if you assume a linear probability model for the survival probability model. Please also read the FAQ at systemfit's website: http://systemfit.org/ I think that you need to derive the log-likelihood function (and preferably also its first derivatives) and maximise this function, e.g. with packages/function maxLik. Best regards, Arne |

nlssystemfit using SUR method [ reply ] By: Francisco Goes on 2014-08-31 10:39 | [forum:41408] |

For my master thesis I have fitted an individual tree diameter growth model and a survival probability model separately using R, but I was told that simultaneous estimation of these two models would minimize overall errors and provide a variance-covariance matrix as a whole. In that respect, can you please tell me if I can do it with nlssystemfit using SUR (seemingly unrelated regression) method? If not, how can I do it in R? My equations are: - tree diameter growth model d_richards_k<-d2~A*(1-exp(-(k0+k1*puro+k2*GL1/100+k3*1/G1+k4*Tmedmax/100+k5*Perc_G_ec1))*(1-(d1/A)^(1-m)))^(1/(1-m)) nls_d_richards_k<-nlsLM(d_richards_k,start=list(A=100,k0=0.6,k1=0,k2=0,k3=0,k4=0,k5=0,m=0.6),control=nls.lm.control(maxiter=500)) - survival probability model mortal_final<-glm(sobrev~Verao+alto_fuste:puro+IC1arv+G1+Perc_G_ec1,family=binomial) Thank you! |