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kc
Quartz | Level 8 kc
Quartz | Level 8

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.

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SteveDenham
Jade | Level 19

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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SteveDenham
Jade | Level 19

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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