Simulate from a fitted glmmTMB model

Mollie Brooks

2021-07-13

glmmTMB has the capability to simulate from a fitted model. These simulations resample random effects from their estimated distribution. In future versions of glmmTMB, it may be possible to condition on estimated random effects.

library(glmmTMB)
library(ggplot2); theme_set(theme_bw())

Fit a typical model:

data(Owls)
owls_nb1 <- glmmTMB(SiblingNegotiation ~ FoodTreatment*SexParent +
                             (1|Nest)+offset(log(BroodSize)),
                          family = nbinom1,
                          ziformula = ~1, data=Owls)

Then we can simulate from the fitted model with the simulate.glmmTMB function. It produces a list of simulated observation vectors, each of which is the same size as the original vector of observations. The default is to only simulate one vector (nsim=1) but we still return a list for consistency.

simo=simulate(owls_nb1, seed=1)
Simdat=Owls
Simdat$SiblingNegotiation=simo[[1]]
Simdat=transform(Simdat,  
            NegPerChick = SiblingNegotiation/BroodSize, 
            type="simulated")
Owls$type = "observed"  
Dat=rbind(Owls, Simdat) 

Then we can plot the simulated data against the observed data to check if they are similar.

ggplot(Dat,  aes(NegPerChick, colour=type))+geom_density()+facet_grid(FoodTreatment~SexParent)