Confidence level…Reliability and n

[Steve001]

Good day,
I would like to ask about the application of confidence level at shop.

For example, if we are buying mobile from shop and we do random selection test. How can identify number of sample, what is the confidence level that we need and how I can calculate the number of sample that we need to test
Regards,

[David]

Hi Steve,

You might want to take a look at http://www.weibull.com/LifeDataWeb/test_design.htm. This link discusses the Design of Reliability Tests utility in Weibull++. This utilizes the Cumulative Binomial distribution. Additional information can also be found at http://www.weibull.com/hotwire/issue24/relbasics24.htm.

I hope this helps.

[Steve001]

Hi Steve,

You might want to take a look at http://www.weibull.com/LifeDataWeb/test_design.htm. This link discusses the Design of Reliability Tests utility in Weibull++. This utilizes the Cumulative Binomial distribution. Additional information can also be found at http://www.weibull.com/hotwire/issue24/relbasics24.htm.

I hope this helps.

Hi David,
It is very useful infomation. Howevevr, i do not what do mean by Beta; and how to select the right value

Thanks

[David]

Hey Steve,

Beta is the shape parameter for the Weibull distribution. This is a value that you would assume based on passed history or general knowledge regarding what you expect the failure rate characteristics to be (i.e. infant mortality, constant or wear-out). This value is only used if the required time for the goal does not equal your test time or if specifying a goal based on MTTF. The general process for how this value is used is presented in http://www.weibull.com/LifeDataWeb/test_design.htm. Please see the sections Determining Units for Available Time and Weibull Distribution Example - Demonstrate MTTF. Other distributions could also be used (lognormal, exponential, etc.) and their correpsonding parameter and equations would be used. The examples in the links that I provided previously assumed the Weibull distribution. Keep in mind that the reliability in the Binomial equation is the reliability at the test time, RTest.

I hope this helps to clear up the confusion.