Hi Ken,
I get pretty much the same numbers as the other replies. Binomial
assumes independent and equally likely. The Poisson is an approximation of
the Binomial under certain conditions (large sample size (n), small defect
percentage (p), and n x p< or = 7, or so says my thick Stats book).
Your question is the same as inspection sampling. Except with
inspection sampling, they also through in the Hypergeometric. (Here's one of
those terms to through out and impress your friends!) With reliability,
failures are a function of time. However, with software, there is no time
dependance (i.e. no aging).
Using Excel,
Binomial:
Sample Size (X) Failures (Y)
---------------------- ----------------
76 0
129 1
176 2
221 3
265 4
308 5
Poisson:
Sample Size (X) Failures (Y)
---------------------- ----------------
70 0
118 1
162 2
203 3
242 4 Violates Rule, use Binomial
281 5 Violates Rule, use Binomial
Glenn
Ken Patel <[log in to unmask]> Wrote:
|
| Reliability/Quality Guru,
| I received this question from our engineering department.
|
| Currently, they are seeing 1 system crash out of 10 times. They want to
| improve the crash rate to 1 failure every 30 times with 90% confidence
| level. They want to know how many operation "X" they will run with no more
| than "Y" failures with 90% confidence level which will yield 1 failure every
| 30 times.
|
| I do not know how to solve it as haven't practiced it. Am I providing enough
| information or what information is needed to make a sense out of it? What
| kind of model it will fit, Poisson, Binomial, etc?
|
| Any help will be highly appreciated.
|
| re,
| ken patel
|
|
| ______________________________________________________
| Ken Patel Phone: (408) 490-6804
| 1708 McCarthy Blvd. Fax: (408) 490-6859
| Milpitas, CA 95035 Beeper: (888) 769-1808
|
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