# Re: [R] poisson mean hypothesis

From: Jan Wijffels <Jan.Wijffels_at_ucs.kuleuven.be>
Date: Mon 12 Sep 2005 - 20:11:50 EST

Jan

-----Original Message-----
From: Dimitris Rizopoulos [mailto:dimitris.rizopoulos@med.kuleuven.be] Sent: maandag 12 september 2005 11:33
To: Jan Wijffels
Cc: r-help@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

```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@ucs.kuleuven.be> To: <r-help@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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