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I am trying to understand the zero-inflated poisson (ZIP) model used in Bayesian regression modelling. I came across code here for the ZIP model. My question is related to the 3rd line of code within the for loop, that is:

phi[i]<- -LL[i]+10000

I am not sure why the 10,000 is used here. For instance, when you look at appendix A for the ZIP regression Winbugs code in a paper found here, there is no use of this 10,000. Any clarification would be appreciated

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This is the zero’s trick used to define a new sampling distributions in WinBUGS. Check the manual about defining new sampling distributions or see here.

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  • $\begingroup$ one more question.......as shown by the paper which does not use the '10,000', does it mean the zero trick is not always needed? $\endgroup$
    – user121
    Commented Sep 14, 2018 at 4:57
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    $\begingroup$ In the mathematical definition of the model you don’t need it. It’s just a trick used in WinBUGS. $\endgroup$
    – Dimitris Rizopoulos
    Commented Sep 14, 2018 at 5:06

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