From: Duncan Murdoch <murdoch_at_stats.uwo.ca>

Date: Sun, 06 Jan 2008 10:01:15 -0500

*>
*

> I thought I should show what I did, this is R 2.6.1:

*>
*

*> tghyper(a=-1, k=-1, N=5) %I think this makes it do Beta Negative Binomail
*

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Date: Sun, 06 Jan 2008 10:01:15 -0500

On 06/01/2008 9:36 AM, Nasser Abbasi wrote:

> I think I should have posted this question here as well. I am posting my

*> question here since it is R related. Please see below. I originally posted
**> this to sci.stat.math
**>
**>
**> "Nasser Abbasi" <nma_at_12000.org> wrote in message
**> news:Mm4gj.28843$R92.4987_at_newsfe16.phx...
*

>> I think R documentation is a bit hard for me to sort out at this time. >> >> I was wondering if someone who knows R better than I do could please let >> me know the command syntax to find the mean of Beta Negative Binomial >> Distribution for the following parameters: >> >> n=3 >> alpha=0.5 >> beta=3 >> >> Here is the documenation page for R which mentions this distribution >> >> http://rweb.stat.umn.edu/R/library/SuppDists/html/ghyper.html >> >> Using Mathematica, I get (-18) for the mean and -150 for the variance, >> and wanted to verify this with R, since there is a negative sign which is >> confusing me.

A variance could not be negative, so clearly Mathematica has it wrong.

>> >> Mathematica says the formula for the mean is n*beta/(alpha-1) and that >> is why the negative sign comes up. >> alpha, beta, n can be any positive real numbers. >> >> If someone can just show me the R command for this, that will help, I have >> the R package SuppDists installed, I am just not sure how to use it for >> this distribution. >> >> thanks, >> Nasser >>

> I thought I should show what I did, this is R 2.6.1:

It reports itself as

> tghyper(a=-1, k=-1, N=5)

[1] "type = IV -- x = 0,1,2,..."

which I believe indicates Beta-negative-binomial.

*>
*

> and now I used summary command, right?

*>
**> sghyper(3, .5, 3)
*

Why did you change the parameters? If you used the same ones as above, you get

> sghyper(a=-1, k=-1, N=5)

$title

[1] "Generalized Hypergeometric"

$a

[1] -1

$k

[1] -1

$N

[1] 5

$Mean

[1] 0.2

$Median

[1] 0

$Mode

[1] 0

$Variance

[1] 0.36

$SD

[1] 0.6

$ThirdCentralMoment

[1] 1.176

$FourthCentralMoment

[1] 8.9712

$PearsonsSkewness...mean.minus.mode.div.SD [1] 0.3333333

$Skewness...sqrtB1

[1] 5.444444

$Kurtosis...B2.minus.3

[1] 66.22222

I don't know if those values are correct, but at least they aren't nonsensical like the ones you report from Mathematica.

*>
*

> But I do not think this is correct.Tried few other permitations. Hard for me

*> to see how to set the parameters correctly for this distribution.
**>
**> thanks,
**> Nasser
**>
**> ______________________________________________
**> R-help_at_r-project.org mailing list
**> 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.
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