Six Sigma Defect Metrics
Before we go ahead, lets define two terms:
- A Six Sigma defect is defined as anything outside of customer specifications.
- A Six Sigma opportunity is the total quantity of chances for a defect.
Here are various formulae to measure different metrics related to Six Sigma Defects
Defects Per Unit – DPU
Total Number of Defects
DPU = ------------------------
Total number of Product Units
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The probability of getting ‘r’ defects in a sample having a given dpu rate can be predicted with the Poisson Distribution.
Total Opportunities – TO
TO = Total number of Product Units x Opportunities
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Defects Per Opportunity – DPO
Total Number of Defects
DPO = ------------------------
Total Opportunity
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Defects Per Million Opportunities – DPMO
DPMO = DPO x 1,000,000
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Defects Per Million Opportunities or DPMO can be then converted to sigma values using Yield to Sigma Conversion Table given in Six Sigma – Measure Phase.
According to the conversion table
6 Sigma = 3.4 DPMO
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How to find your Sigma Level
- Clearly define the customer’s explicit requirements.
- Count the number of defects that occur.
- Determine the yield– percentage of items without defects.
- Use the conversion chart to determine DPMO and Sigma Level.
Simplified Sigma Conversion Table
If your yield is: Your DPMO is: Your Sigma is:
30.9% 690,000 1.0
62.9% 308,000 2.0
93.3 66,800 3.0
99.4 6,210 4.0
99.98 320 5.0
99.9997 3.4 6.0