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Topic: chi-square in confidence interval for failure rate
Replies: 2   Last Post: Mar 16, 2013 11:44 PM

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Paul

Posts: 263
Registered: 2/23/10
chi-square in confidence interval for failure rate
Posted: Mar 16, 2013 10:09 PM
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All the info I found online for estimating failure rate from the
number of failures over a time period make reference to chi-squre, but
without actually describing how it comes about. The most helpful
explanation I found is http://www.weibull.com/hotwire/issue116/relbasics116.htm.

However, I'm missing some fundamental intuition behind the starting
point (equation 5). It is assumed that we see r failures over a time
period T. The probabilities for 0 to r failures are summed up and
related to the confidence level. Why is this equation true? I mean,
we do not see 0 to r failures, we only see r failures, so why so those
lesser failure counts come into the picture at all?

Thanks if anyone can refer to an online explanation. If it is
offline, I can probably get it eventually, but online would be so much
more suitable for my timeframe.



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