[R] glmmADMB model fails when fixed effect interaction term is removed

cara715 capplestein at cnlm.org
Mon Jan 5 22:14:22 CET 2015


I am looking at a data set predicting number of plants (FERO) based on fixed
effects sowing method (Method) and sowing rate (Rate). I also have a slope
random effect for the site and intercept random effects for the nested
variables Block and Strip.ID (to account for experimental design). I have
tried running several different models using the glmmadmb function. The
dependent variable, FERO, is a discrete count. All of my fixed and random
effects are categorical and have the following levels:

Method: 3
Rate: 5
Site: 3
Block: 18
Strip.ID: 275

The following model runs without a problem:

fit_nbin3 <-glmmadmb(FERO ~ Method * Rate + (FERO|Site) +
data = data1, family = "nbinom")

However, when I try to run the same model without the interaction term:

fit_nbin4 <-glmmadmb(FERO ~ Method + Rate + (FERO|Site) +
+ data = data1, family = "nbinom")

I get the following error message:

Parameters were estimated, but not standard errors were not: the most likely
problem is that the curvature at MLE was zero or negative
Error in glmmadmb(FERO ~ Method + Rate + (FERO | Site) + (1 |
Block/Strip.ID),  : 
  The function maximizer failed (couldn't find STD file) Troubleshooting
steps include (1) run with 'save.dir' set and inspect output files; (2)
change run parameters: see '?admbControl'
In addition: Warning message:
running command 'C:\windows\system32\cmd.exe /c
-maxfn 500 -maxph 5 -noinit -shess' had status 1

I am confused as why removing the interaction term, which should simplify
the model is causing it to fail to run correctly. Any ideas what's going on

Here is a sample of my first few lines of data:

Site         Method         Rate  Block  Strip  FERO
Glacial      Broadcast      A      A        H     69	
Glacial      Broadcast      A      A        H     1
Glacial      Broadcast      A      A        H     41

One other quick thing:
I can't seem to the the aictab function to work on the properly run glmmadmb
models. I get a message saying: 	
Error in formatCands(cand.set) : 
Functions do not support mixture of model classes

Thanks in advance for your help!

Cara Applestein
Prairie Science Technician
Center for Natural Lands Management
Olympia, Washington

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