Hello,
I get a warning in SAS saying "WARNING: Scaling the covariance is not available for zero-inflated models." when I use the scale=d option in the model statement of proc genmod.
Any idea of how to handle overdispersion if scale option isn't available for these models? Using some other procedures to run a zip or zinb models, perhaps?
Ideas welcome - thanks in advance.
I had two ideas, but neither worked. First I thought to use PSCALE and use Pearson scaling rather than deviance scaling. Then I tried calculating the deviance scale by hand, and feeding that in as a fixed scale. Both gave the error you reported.
I am left with trying a mixture of two negative binomials or Poisson using PROC FMM. There is an example for handling an overdispersed Poisson as a mixture of two binomial series here . Perhaps this could be adapted for your use.
SteveDenham
I had two ideas, but neither worked. First I thought to use PSCALE and use Pearson scaling rather than deviance scaling. Then I tried calculating the deviance scale by hand, and feeding that in as a fixed scale. Both gave the error you reported.
I am left with trying a mixture of two negative binomials or Poisson using PROC FMM. There is an example for handling an overdispersed Poisson as a mixture of two binomial series here . Perhaps this could be adapted for your use.
SteveDenham
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