Bug in BINOMIAL_ICDF

[Tim Wessman]

(10-18-2015 06:23 PM)Arno K Wrote:  On writing a program for the kind of hypothesis test that are usual in Germany I discovered the following bug: BINOMIAL_ICDF() does not provide the result below the given probability, instead it results to the nearest integer value:
BINOMIAL_ICDF(20,0.6,0.05) -> 8
BINOMIAL_CDF(20,0.6,8) -> 0.0565 which is too big.
The oncalc-help says:
Returns the number of successes, k, out of n trials, each with a probability of p, such that the probability of k or fewer successes is q.
So, in my opinion, it should return 7, not 8.
Arno

So help me understand your thinking here. I'm sick today and not thinking well so chances are I am just not understanding right.

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?