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Defectives V/s Binomial Distribution Process Capability Analysis

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Hello Team,


Just a query would like to clear..... I am working on a GB project where I have collected some data (Discrete/Attrbute).


Currently I am in Measure Phase, where I need to measure the sigma value of the data. The data which I have collected is "Defectives", I need to compute Z value or sigma value. I have used sigma calculator which was shared during GB training from benchmark.


Below mentioned are the details used in sigma calculator :

1) Defective Count - 92
2) Sample Size - 197
3) Yield - 53.30%
4) Z. Bench Sigma Value (LT) - 0.08
5) Z. Bench Sigma Value (ST) - 1.58


I also tried using Capability Analysis using Binomial Distribution of Defectives by using same data in Minitab 16. I have taken 197 as a constant subgroup size


But Process Z value has shown 2.1228. (See attached file)


I am stucked which z value to be followed.


Please advice..




Rajiv N



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  • 1 month later...

Hi Rajiv,


Thanks for posting here and sorry for the delayed response. Do not know how I missed this one.


It looks to me that Minitab is correctly used. However, in the calculator, the sample size is taken as 197 which does not seem to be correct. Please add the samples for all 91 instances in the column. The value should be 5444. 


Now if you use the sigma level calculator with 92 defectives and samples as 5444, you shall get Zlt same as 2.12 (as you got from Minitab)


Hope this helps, Please feel free to ask further. 

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