ZI model problem

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ZI model problem

I am trying to fit a zero-inflated model using zeroinfl() from the pscl library. I have 5 variables:

“agonCount” which is my response variable (numeric: frequency of aggressions).

“season” (factor, with 2 levels: wet and dry),

“subact”  (factor, with 2 levels: fe (feeding) and nfe (non-feeding))

“subclass”  (factor, with 3 levels: S –small-, M –medium- and L –large-)

“act2”  (factor, with 2 levels: immigrant and resident).


In order to run an analysis with ZI (Poisson or Negative Binomial) model I created a ZIP saturated and ZINB saturated model, but when I tried to run ZINB I get the following error:


Error in solve.default(as.matrix(fit$hessian)) :

  system is computationally singular: reciprocal condition number = 3.84232e-17


Thus, I can’t run lrtest (in order to compare the models and choice the better one) because a new error message appears.


The script I used was:




Zip1 <- zeroinfl(f1, dist = "poisson",link = "logit", a)


Zinb1 <- zeroinfl(f1, dist = "negbin",link = "logit", a)


I appreciate your time and input. Thank you
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Re: ZI model problem

Alisa Zhao
Hi Juancho,

Did you figure out why you had this error? This happened to me as well, though I only one categorical variable as my predictor. Thanks!