On May 24, 2012, at 1:57 PM, Nathan Svoboda wrote:
Greetings,
I am trying to fit a zero-inflated Poisson model using zeroinfl()
from the
pscl library. I have 5 covariates (4 continuous, 1 categorical); the
categorical variable has 7 levels. I have had success fitting
models that
contain only the continuous covariates; however, when I add the
categorical
variable to any of the models (or if I run it by itself) I get the
following
error:
Error in solve.default(as.matrix(fit$hessian)) :
system is computationally singular: reciprocal condition number =
3.46934e-20
The code I am using is:
library(pscl)
f1 <- formula(LOCS ~ as.factor(LCOVER) + D_ROADS + D_WATER + D_EDGE +
D_GRASS)
ZIP1 <- zeroinfl(f1, dist="poisson", link = "logit", data = FAWNS)
There is no correlation between my covariates. Also, I tried
reducing my
categorical covariate to 3 levels and still receive the same error.
Can
anyone suggest why I may be getting this error when I add the
categorical
covariate?
What does this show:
with( FAWNS, table(LOCS, LCOVER) )
--
David Winsemius, MD
West Hartford, CT
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