One step in a Six Sigma roadmap involves measuring an organization’s current performance. This is a crucial step because having a long-term measurement “infrastructure” is a key building block for a full organization Six Sigma system.
One way to measure current performance is develop baseline defect measures and identify improvement opportunities. There are two ways of doing this.
First is to determine the fraction or percentage of item samples that had one or more defects. This is also called Proportion Defective. The second way is to determine the fraction of the total units produced and/or delivered that is defect-free, called Final Yield.
Six Sigma allows you to adjust measures according to the number of “opportunities” for defects. The main steps in defining the number of opportunities are:
a. develop a preliminary list of defect types
b. determine which are the actual, customer-critical, specific defects
c. check the proposed number of opportunities against other standard
There are several ways to calculate and express measures based on defect
opportunities.
1. Defect per Opportunity, or DPO - expresses the proportion of defects over the total number of opportunities in a group.
Formula: Number of Defects
# of Units x # of Opportunities
Service Example:
52 defects on applications = .052 DPO
250 apps. X 4 opportunity/app
*The service has a five-percent chance of having a defect in one category.
Manufacturing Example:
52 defects on microchips =.00046 DPO
750 chips x 150 opportunities/chip
2. Defects per Million Opportunities, or DPMO - indicates how many defects would arise if there were one million opportunities. In manufacturing, DPMO is often called PPM (parts per million).
Formula: DPO x 1,000,000 (10 to the 6th power)
Service Example: Loan applications –> .052 x 10 to the 6th power = 52,000 DPMO
Manufacturing Example: Microchips –> .00046 x 10 to the 6th power = 460 DPMO
3. Sigma Measure - translate your defect measure-usually by DPMO-by using a conversion table.
Sigma Measure Formula: Calculate DPMO, Consult Table
Service Example: Loan applications –> 52,000 DPMO = 3.1 Sigma
Manufacturing Example: Microchips –> 460 DPMO = 2.3 Sigma
The Six Sigma Way: How GE, Motorola, and Other Top Companies are Honing Their Performance
Yield to Sigma Conversion Table
