View Full Version : equip. failure

Outlier

07-22-2010, 01:39 PM

A widget fails each month for six months. A fix is then installed.

How many months of no failures would need to go by before I can be 95% confident that the problem is fixed?

How is this calculated?

I wrote a paper on this and cannot find it for the life of me.

Are you going to test

H_0: p = \frac {1} {6} vs H_1: p = 0

with the number of months of no failure \sim Geometric(p) ?

Outlier

07-22-2010, 06:56 PM

I used a binomial distribution. Maybe that was incorrect. I'll have to find that paper. :confused:

Could it have been a poisson distribution with a rate parameter? I ask because you stated that there was 1 event/month.

Outlier

07-22-2010, 09:32 PM

How would you all recommend I do this?

Following a Poisson distribution:

Pr(N_{t}=k)=f(k;\lambda t)=\frac{(\lambda t)^{k}e^{-\lambda t}}{k!}, where \; \lambda =1

f(0;\lambda *1)=0.37

f(0;\lambda *2) =0.14

f(0;\lambda *3)=0.05

So three months.

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