Hello list,

I want to model the abundance of a aquatic bird using three predictors and
I am trying to fit a Hurdle model using the R package ‘pscl’.

When I try to fit a model with interaction between predictors, R give me an
error:

hurdle(formula = carbototal ~ anchomedio:distdormidero, data =
ModHurdle300, dist = "negbin")
Error en solve.default(as.matrix(fit_count$hessian)) :
  system is computationally singular: reciprocal condition number = 0


The error is the same for all models with interaction between predictors:

  formula = carbototal ~ anchomedio:distdormidero
  formula = carbototal ~ anchomedio:distpistacar
  formula = carbototal ~ anchomedio:distdormidero:distpistacar

  Being: anchomedio, river width; distdormidero, distance to the nearest
roost and      distpistcar, distance to nearest road.


and for the three data sets of increasing sampling size: ModHurdle100,
where N=100; ModHurdle200, where N=200; ModHurdle300, where N=300. With the
exception of "formula = carbototal ~ anchomedio:distpistacar" for
ModHurdle100 data set, which the program seems able to handle without error.

Is there anything I can do to solve this error? O maybe those models cannot
be fitted?

Greetings and thanks in advance for your attention.

-- 
*Yaiza Iglesias González*
*
Dpto.Zoología y Antropología Física
Facultad de Biología- Universidad de Santiago de Compostela
Rúa Lope Gómez de Marzoa, s/n. Campus Vida.
15782 Santiago de Compostela

yaiza.iglesias.ba@gmail.com
*
*
*

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