Hi Duncan and Rlist, I've notice a different behaviour in the invbinomial you suggest me and invbinomial in stata.
invbinomial(50,50, 0.4) Error in uniroot(function(x) pbinom(k, n, x) - p, c(0, 1)) : f() values at end points not of opposite sign > invbinomial(50,50, 0.6) Error in uniroot(function(x) pbinom(k, n, x) - p, c(0, 1)) : f() values at end points not of opposite sign while stata gen p3=invbinomial(50,50, 0.4) . display p3 0 . gen p4=invbinomial(50,50, 0.6) . display p4 0 Thanks Cheers Anna ________________________________ Da: Duncan Murdoch <murdoch.dun...@gmail.com> Cc: Rcran help <r-help@r-project.org> Inviato: Giovedì 31 Maggio 2012 15:32 Oggetto: Re: [R] inverse binomial in R On 12-05-31 9:10 AM, anna freni sterrantino wrote: > Hello! > I'm having some trouble > trying to replicate in R a Stata function > > invbinomial(n,k,p) > Domain n: 1 to 1e+17 > Domain k: 0 to n - 1 > Domain p: 0 to 1 (exclusive) > Range: 0 to 1 > Description: returns the inverse of the cumulative binomial; i.e., it > returns the probability of success on one trial such > that the probability of observing floor(k) or fewer > successes in floor(n) trials is p. > > I've found some hints on the web like > http://rwiki.sciviews.org/doku.php?id=guides:tutorials:regression:table > > I tried to replicate using qbinom > the results obtained in > >> invbinomial(10,5, 0.5) >> .54830584 > > but with no success. I don't think base R has a function like that, though some contributed package probably does. If you're writing it yourself you'd need to use uniroot or some other solver, e.g invbinomial <- function(n, k, p) { uniroot(function(x) pbinom(5, 10, x) - p, c(0, 1)) } [[alternative HTML version deleted]]
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