Displaying 3 results from an estimated 3 matches for "habdiv".
2007 Jun 12
0
nlme model
...out the right form for the nlme arguments. I do have examples in Modern and Applied Statistics with S and from other sources, but I still can't figure it out.
I am trying to estimate species richness (sr) in streams across minnesota. My predictor variables are depth (d), habitat diversity (habdiv), drainage area (da) and an indicator variable representing the watershed/basins that the streams are in (bas: there are 10 watersheds). The variable explaining the greatest amount of variation appears to be da. I have used a log(da) to linearize the relationship, but an asymptotic relationship i...
2007 Jul 18
0
multicollinearity in nlme models
I am working on a nlme model that has multiple fixed effects (linear and nonlinear) with a nonlinear (asymptotic) random effect.
asymporig<-function(x,th1,th2)th1*(1-exp(-exp(th2)*x))
asymporigb<-function(x,th1b,th2b)th1b*(1-exp(-exp(th2b)*x))
mod.vol.nlme<-nlme(fa20~(ah*habdiv+ads*ds+ads2*ds2+at*trout)+asymporig(da.p,th1,th2)+
asymporigb(vol,th1b,th2b),
fixed=ah+ads+ads2+at+th1+th2+th1b+th2b~1,
random=pdBlocked(list(th1~1,th2~1)),
start=c(ah=.5524,ads=.8,ads2=-.1,at=-1,th1=2.542,th2=-7.117,th1b=2,th2b=-7),
data=pca1.grouped,verbose=T)
I am looking at...
2007 Jun 20
1
nlme correlated random effects
I am examining the following nlme model.
asymporig<-function(x,th1,th2)th1*(1-exp(-exp(th2)*x))
mod1<-nlme(fa20~(ah*habdiv+ad*log(d)+ads*ds+ads2*ds2+at*trout)+asymporig(da.p,th1,th2),
fixed=ah+ad+ads+ads2+at+th1+th2~1,
random=th1+th2~1,
start=c(ah=.9124,ad=.9252,ads=.5,ads2=-.1,at=-1,th1=2.842,th2=-6.917),
data=pca1.grouped)
However, the two random effects (th1 and th2) which describe the asymptotic re...