[ADMB Users] glmmadmb, nbinom and alpha
dave fournier
davef at otter-rsch.com
Sat Aug 24 11:56:45 PDT 2013
If you are willing to hack the tpl file a bit the overdispersion is
equal to the parameter tau
in the code .i.e var = tau * mu for a neg bin with mean mu and variance
var.
For the truncated case this is modified in ADMB to
double tau=3.0;
double mu=1.0;
double p0=exp(log_density_negbinomial(0,mu,tau));
double trunc_var=(tau*mu+square(mu))/(1-p0)-square(mu/(1-p0));
cout << "variance of truncated dist = " << trunc_var << endl;
produces
variance of truncated distribution = 3.86603
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