two queries on distribution

Ottar N. Bjornstad (bjornsta@nceas.ucsb.edu)
Sat, 03 Jan 1998 11:46:20 +0100


Dear All,

I have two questions about the gamma distribution and the negative binomial distribution (in Splus 4):

1) Why does the Gamma distribution only have 1 parameter (the shape parameter) in Splus, when the usual Gamma is a two parameter distribution?

2) I'm really confused about the Negative binomial:
- Venables & Ripley provided a function rnegbin that takes two parameters: the mean and the shape parameter.
- Splus 4 has a function for the negative binomial called rnbinom that takes two parameters (size, and probability). What is the relationship between the two? can I use the new rnbinom like I use the rnegbin - to generate overdisperesed poisson data (by specifying the shape parameter)?

Gratefully yours,
Ottar Bjornstad

--------------------------------------------
Ottar N. Bjornstad
Until 2nd of April:
mailto:bjornstad@nceas.ubsc.edu
NCEAS, 735 State St., Suite 300, Santa Barbara, CA 93101-3351
Tel. + 1 (805) 892 2511, Fax. + 1 (805) 892 2510
http://www.uio.no/~ottarnb/