From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>

Date: Fri 03 Feb 2006 - 14:47:07 GMT

Date: Fri 03 Feb 2006 - 14:47:07 GMT

(Ted Harding) <Ted.Harding@nessie.mcc.ac.uk> writes:

> On 03-Feb-06 uht@dfu.min.dk wrote:

*> > Full_Name: Uffe Høgsbro Thygesen
**> > Version: 2.2.0
**> > OS: linux
**> > Submission from: (NULL) (130.226.135.250)
**> >
**> >
**> > Hello all.
**> >
**> > pbinom(q=0,size=0,prob=0.5)
**> >
**> > returns the value NaN. I had expected the result 1. In fact any
**> > value for q seems to give an NaN.
**>
**> Well, "NaN" can make sense since "q=0" refers to a single sampled
**> value, and there is no value which you can sample from "size=0";
**> i.e. sampling from "size=0" is a non-event. I think the probability
**> of a non-event should be NaN, not 1! (But maybe others might argue
**> that if you try to sample from an empty urn you necessarily get
**> zero "successes", so p should be 1; but I would counter that you
**> also necessarily get zero "failures" so q should be 1. I suppose
**> it may be a matter of whether you regard the "r" of the binomial
**> distribution as referring to the "identities" of the outcomes
**> rather than to how many you get of a particular type. Hmmm.)
**>
**> > Note that
**> >
**> > dbinom(x=0,size=0,prob=0.5)
**> >
**> > returns the value 1.
**>
**> That is probably because the .Internal code for pbinom may do
**> a preliminary test for "x >= size". This also makes sense, for
**> the cumulative p<dist> for any <dist> with a finite range,
**> since the answer must then be 1 and a lot of computation would
**> be saved (likewise returning 0 when x < 0). However, it would
**> make even more sense to have a preceding test for "size<=0"
**> and return NaN in that case since, for the same reasons as
**> above, the result is the probability of a non-event.
*

Once you get your coffee, you'll likely realize that you got your p's and d's mixed up...

> (But it depends on your point of view, as above ... However,

*> surely the two should be consistent with each other.)
**>
**> Best wishes,
**> Ted.
**>
**> --------------------------------------------------------------------
**> E-Mail: (Ted Harding) <Ted.Harding@nessie.mcc.ac.uk>
**> Fax-to-email: +44 (0)870 094 0861
**> Date: 03-Feb-06 Time: 14:34:28
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*

-- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-develReceived on Sat Feb 04 01:55:14 2006

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