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. (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
