80/80 Rule

[approach]

Without going into the mathematics, you can demonstrate that
your product meets an 80 / 80 requirement with eight units
all of which meet the requirement.

The mathematics is based upon the Binomial Distribution.
The first 80 is the probability of success.  The second 80
is the confidence that all units will meet the requirements
with an 80 % probability of success.

The mathematics makes no assumption on the distribution, for
example, whether the test data has a normal (Gaussian)
distribution.

The Binomial Distribution, b(x;,n,p), is used to calculate
the expected number of success in x out of n trials for a
given p Probability of Success

b(x;n,p) = ( (n!)*(p^n)*((1-p)^(n-x))/((x!) * ((n-x)!))

The Cummulative Binomial Distribution, B((x-1);n,p), is used
to calculate the confidence demonstrated by x successes ofut
of n trials for a give p Probabilityof Scccess.

Here is a short table of  results

1 unit tested, 1 unit passed, 50 % probability of success,
50 % confidence
2 units tested, 2 units passed, 60 % probabilityof success,
60 % confidence
3 units tested, 3 units passed, 65 % probability of success,
65 % confidence
4 units tested, 4 units passed, 70 % probability of success,
70 % confidence
5 units tested, 5 units passed, 75 % probability of success,
75 % confidence
8 units tested, 8 units passed, 80 % probability of success,
80 % confidence
14 units tested, 13 units passed, 80 % probability of
success, 80 % confidence
21 units tested, 19 units passed, 80 % probability of
success, 80 % confidence

Best regards

Bob Schlentz




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Re: Sound Engineering Practice

[approach]

Tongue-In-Check Answer:  Sound Engineering Practice never
makes a mistake.

Practical Answer:  Perform a risk analysis and fix any
hazards.  Remember that the risk analysis covers intended
and unintended uses and normal and abnormal conditions.

In the United States, the signature of a Professional
Engineer on the drawings is usually accepted by a Court that
sound engineering practices were followed.  I think that is
true in Europe, but I do not have personal knowledge of
that.

Best Regards

Bob Schlentz
appro...@minn.net




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