# Statistics expert - cumulative binomial stuff

#### roscoe

##### Well-known Member
My job requires me to establish the appropriate sample size during very expensive flight testing (i.e. can't afford to do more testing than the minimum required to establish the appropriate confidence). I have a nomograph that was given to me that we use to calculate the right value given confidence and demonstrated reliability (i.e. results). The nomograph can be found at: https://acc.dau.mil/docs/dtepi/pns/doc/nomogr/bdi.pdf.

Assuming we want to show that we have 80% confidence (right axis) that we'll succeed 80% of the time (left axis, also called reliability), I connect those values on each side with a straight edge and the chart shows that with zero failures (upper right boundary) we need 7 trials. If we have one failure (upper left boundary) the chart shows that we need 12 trials (11 successes). I was provided a formula that defines the zero failure curve [n=Log (1-confidence)/Log (reliability)]...What I need is a more generic equation or excel function that will generate these curves with failures not equal to zero.

Any statistics experts out there that can help me?

Thanks

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Nobody?

Last edited:
Nope. We've been doing this for years because it's "the way we've always done it". I hate that and want to be able to support the numbers.

As for the pages you reference, those are over my head (I've forwarded them to the prob/stats expert in the office.

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