[R] poisson mean hypothesis

[Jan Wijffels]

Dimitris,
Thanks for the test. But you are using a normal approximation to the
poisson distribution. This is not applicable in my case. I was more
looking for an exact test. Probably based on Garwood's (1936) confidence
interval. If there is already an R implementation available, than this
would be helpful for me.

Jan

-----Original Message-----
From: Dimitris Rizopoulos [mailto:dimitris.rizopoulos at med.kuleuven.be] 
Sent: maandag 12 september 2005 11:33
To: Jan Wijffels
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] poisson mean hypothesis

you could use something like the following (in case of two-group 
comparisons make the proper adjustements):

pois.test <- function(x, alternative = c("two.sided", "less", 
"greater"), mu){
    alternative <- match.arg(alternative)
    if (missing(mu) || (length(mu) != 1 || is.na(mu)))
        stop("'mu' must be a single number")
    nx <- length(x)
    mu.x <- mean(x)
    stat <- (mu.x - mu) / sqrt(mu.x/nx)
    p.value <- switch(alternative,
        "two.sided" = 2 * pnorm(-abs(stat)),
        "less" = pnorm(stat),
        "greater" = pnorm(stat, lower = FALSE))
    list("sample mean" = mu.x, "null mean" = mu, "alternative" = 
alternative,
            statistic = stat, p.value = p.value)
}
################

y <- rpois(50, 5)
pois.test(y, alt = "g", mu = 4)

y <- rpois(30, 15)
pois.test(y, alt = "l", mu = 16)


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Jan Wijffels" <Jan.Wijffels at ucs.kuleuven.be>
To: <r-help at stat.math.ethz.ch>
Sent: Monday, September 12, 2005 10:01 AM
Subject: [R] poisson mean hypothesis


> Dear R-users,
> Is there a way to get p-values for a one-sided hypothesis test about 
> a
> poisson mean?
>
> Thanks,
>
> Jan Wijffels
> University Center for Statistics
> W. de Croylaan 54
> 3001 Heverlee
> Belgium
> tel: +32 (0)16 322784
> fax: +32 (0)16 322831
> <http://www.kuleuven.be/ucs> http://www.kuleuven.be/ucs
>
>
>
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