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))
}