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" <[EMAIL PROTECTED]> wrote in message > news:[EMAIL PROTECTED] >> 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: > > tghyper(a=-1, k=-1, N=5) %I think this makes it do Beta Negative Binomail 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. Duncan Murdoch > > 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@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. ______________________________________________ R-help@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.
