Is there dpois equivalent for zero-inflated Poisson?

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>:

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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