I am using the chi-square funcition to calculate minimal test time (T) in order to demonstrate that the mean time to failure (MTTF) of a product is at least H hours with a confidence level of CL.
I know that I have to use the following formula:
T=MTTF*X(CL,deg)/2
where X(CL,deg) is the chi-square function and deg is the degree number. In all failure analysis text book, deg=2N+2 where N is the number of observed failures. I would like to understand why I have to use this as a degree number.
Because the number of degrees of freedom and confidence level determines the value of Chi square statistics. (..for ezamle in stat tabs..)Is that enough?
Thanks a lot of your answer. I still do not understand why the degrees of failure
are chosen equal to 2*(r+1) where r is the number of failure.
Please refer to: https://www.weibull.com/hotwire/issue116/relbasics116.htm
See this https://www.ti.com/lit/an/sbfa011/sbfa011.pdf?ts=1719613259114&ref_url=https%253A%252F%252Fwww.google.com%252F It explains it completely Cheers!