(Ted Harding) <[EMAIL PROTECTED]> writes: > On 03-Feb-06 [EMAIL PROTECTED] 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... I think Uffe is perfectly right: The result of zero experiments will be zero successes (and zero failures) with probability 1, so the cumulative distribution function is a step function with one step at zero ( == as.numeric(x>=0) ). > (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) <[EMAIL PROTECTED]> > Fax-to-email: +44 (0)870 094 0861 > Date: 03-Feb-06 Time: 14:34:28 > ------------------------------ XFMail ------------------------------ > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > -- 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 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
