Process Capability Analysis

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Defect per unit or DPU, is the average number of defects observed in a population sample. Calculated by dividing the total number of observed defects by the total number of units in the sample:

DPU=(Total number of defects)/(Total units)

Defects per opportunity (opportunity must be a real number, so it won’t affect your quality score) or DPO, is total number of possible errors or defects that could be counted in a process or service:

DPO=(Total Number of Defects Observed)/(Number of Units x Number of Opportunities per Unit)

Defects per Million Opportunities or DPMO, is DPO times million and it takes into consideration the number of opportunities within a part or process. By determining the DPMO, you can then assign the sigma level of the process.

Sigma Values

Sigma values are a metric common to Six Sigma (6σ) organizations and provide a baseline for process performance, also 6σ values can be used to compare products, departments, processes – a “benchmark”.

Important: Although process capability and process variation are highly correlated, do not confuse the “process sigma” with the Greek letter “sigma” (σ) which is used to represent standard deviation.

Once you have the DPMO calculated, you can acquire the Sigma values by looking them up on published tables.

Example of Capability Analysis

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