Bug in BINOMIAL_ICDF

[Arno K]

(10-18-2015 08:50 PM)Tim Wessman Wrote:  You have:

BINOMIAL_CDF(20,0.6,7) -> ~.0210
BINOMIAL_CDF(20,0.6,8) -> ~.0565

The target is .05. There only seems to be one possible result there that works to me. Note that every math program I've tried here agrees it should be 8 as well.

Why then would the inverse not hold true? 7 would be too small. 8 contains your desired target.

Are you advocating a non-integer result? How would that be definted since we are talking about trials here?

Well, I do not use a lot of other mathematics programs and did not check the ones I have, I wrote a program to provide the integer with P(x<=k)<=alpha which is one of the usual hypothesis-tests at least here in German schools, k may not be too big is the aim, and so I awaited BINOMIAL_ICDF to give the proper answer, 7, it was not very difficult to correct that as a simple -1 does the job. I was astonished when I found that P(X>=k)<=0.05 was correctly handled by the Prime, but I will have to check that with other examples.
Ok, when this behaviour is usual then I will not bother anymore.
Thank you
Arno