The statistical definition of Six Sigma allows for 3.4 defects per million.This is achieved by what Cpk index value?
A)6
B)1
C)1.33
D)1.67
E)2

Question

Quizplus · Accepted Answer

The Cpk index value is calculated using the formula: Cpk = min[(USL-mean)/3*standard deviation, (mean-LSL)/3*standard deviation]. 
For Six Sigma, which allows for 3.4 defects per million, we need to have a process capability where the distance from the mean to the nearest specification limit is six standard deviations. 
So, the Cpk value can be calculated as follows: Cpk = min[(USL-mean)/3*standard deviation, (mean-LSL)/3*standard deviation] = min[(6*standard deviation)/3*standard deviation, (6*standard deviation)/3*standard deviation] = 2. 
Therefore, the best choice is E, with a Cpk index value of 2.

The Statistical Definition of Six Sigma Allows for 3