[R] Is there dpois equivalent for zero-inflated Poisson?

[Matti Viljamaa]

Could you clarify what are the parameters and why it’s formulated that way?

-Matti

> On 22 Mar 2016, at 14:17, Thierry Onkelinx <thierry.onkelinx at inbo.be> wrote:
> 
> Dear Matti,
> 
> What about this?
> 
> dzeroinflpois <- function(x, lambda, zero){
>   ifelse(x == 0, zero, 0) + dpois(x, lambda) / (1 - zero)
> }
> plot(x, dzeroinflpois(x, lambda = 10, zero = 0.2), type = "l")
> 
> 
> 
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest 
> team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance 
> Kliniekstraat 25
> 1070 Anderlecht
> Belgium
> 
> To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher
> The plural of anecdote is not data. ~ Roger Brinner 
> The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data. ~ John Tukey
> 
> 2016-03-22 13:04 GMT+01:00 Matti Viljamaa <mviljamaa at kapsi.fi <mailto:mviljamaa at kapsi.fi>>:
> I’m doing some optimisation that I first did with normal Poisson (only parameter theta was estimated), but now I’m doing the same with a zero-inflated Poisson model which
> gives me two estimated parameters theta and p (p is also pi in some notation).
> 
> My question is, is there something equivalent to dpois that would use both of the parameters (or is the p parameter possibly unnecessary)?
> 
> I’m calculating the “fit” of the Poisson model
> 
> i.e. like
> 
> x = c(0,1,2,3,4,5,6)
> y = c(3062,587,284,103,33,4,2)
> fit1 <- sum(y)*dpois(x, est_theta)
> 
> and then comparing fit1 to the real observations.
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> 
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