R help - Mar 2016 - Is there dpois equivalent for zero-inflated Poisson?

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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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.
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
	[[alternative HTML version deleted]]

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.
>         [[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org <mailto:R-help at r-project.org> mailing list
-- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
<https://stat.ethz.ch/mailman/listinfo/r-help>
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
> 

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